Re: [PATCH][expr.c] PR 65358 Avoid clobbering partial argument during sibcall
Hi Jeff,
On 12/05/15 23:04, Jeff Law wrote:
On 05/11/2015 03:28 AM, Kyrill Tkachov wrote:
The more I think about this, the more I think it's an ugly can of
worms and maybe we should just disable sibcalls for partial
arguments. I doubt it's a big performance issue in general.
We already have quite a bit of code in calls.c to detect cases with
partial argument overlap for the
explicit purpose of allowing sibcalls when partial arguments occur in
the general case. However, that
code only detects when a partial argument overlaps with other arguments
in a call. In this PR the
partial argument overlaps with itself. It would be a shame to disable
sibcalls for all partial arguments
when there is already infrastructure in place to handle them.
I didn't even realize we had support for partial arguments in sibcalls. Ah,
Kazu added that in 2005, I totally missed it. I probably would have suggested
failing the sibcall for those cases back then too...
Is there any way to re-use that infrastructure to deal with the case at hand?
In addition to the argument/stack direction stuff, I've been pondering
the stack/frame/arg pointer issues. Your approach assumes that the
incoming and outgoing areas are always referenced off the same base
register. If they aren't, then the routine returns no overlap.
But we'd need to consider the case where we have a reference to the
arg or frame pointer which later gets rewritten into a stack pointer
relative address.
Is it too late at the point were you do the checks to reject the
sibling call? If not, then maybe the overlap routine should return a
tri-state. No overlap, overlap, don't know. The last would be used
when the two addresses use a different register.
Ok, here is my attempt at that. The overlap functions returns -2 when it
cannot staticall compare the
two pointers (i.e. when the base registers are different) and the caller
then disables sibcalls.
The code in calls.c that calls this code will undo any emitted
instructions in the meantime if sibcall
optimisation fails. This required me to change the type of
emit_push_insn to bool and add an extra
parameter, so this patch touches a bit more code than the original version.
Bootstrapped on x86_64 and tested on arm. The testcase in this PR still
performs a sibcall correctly on arm.
What do you think of this?
Thanks,
Kyrill
2015-05-11 Kyrylo Tkachov kyrylo.tkac...@arm.com
PR target/65358
* expr.c (memory_load_overlap): New function.
(emit_push_insn): When pushing partial args to the stack would
clobber the register part load the overlapping part into a pseudo
and put it into the hard reg after pushing. Change return type
to bool. Add bool argument.
* expr.h (emit_push_insn): Change return type to bool.
Add bool argument.
* calls.c (expand_call): Cancel sibcall optimisation when encountering
partial argument on targets with ARGS_GROW_DOWNWARD and
!STACK_GROWS_DOWNWARD.
(emit_library_call_value_1): Update callsite of emit_push_insn.
(store_one_arg): Likewise.
2015-05-11 Honggyu Kim hong.gyu@lge.com
PR target/65358
* gcc.dg/pr65358.c: New test.
Jeff
expr.patch
commit 5b596f10846b6d3b143442a306801c8262d8b10a
Author: Kyrylo Tkachovkyrylo.tkac...@arm.com
Date: Wed Mar 18 13:42:37 2015 +
[expr.c] PR 65358 Avoid clobbering partial argument during sibcall
diff --git a/gcc/calls.c b/gcc/calls.c
index caa7d60..81ef2c9 100644
--- a/gcc/calls.c
+++ b/gcc/calls.c
@@ -3225,6 +3225,13 @@ expand_call (tree exp, rtx target, int ignore)
{
rtx_insn *before_arg = get_last_insn ();
+ /* On targets with weird calling conventions (e.g. PA) it's
+hard to ensure that all cases of argument overlap between
+stack and registers work. Play it safe and bail out. */
+#if defined (ARGS_GROW_DOWNWARD) !defined (STACK_GROWS_DOWNWARD)
+ sibcall_failure = 1;
+ break;
+#endif
So we're trying to get away from this kind of conditional compilation.
Instead we want to write
if (ARGS_GROW_DOWNWARD !STACK_GROWS_DOWNWARD)
ARGS_GROW_DOWNWARD is already a testable value. But STACK_GROWS_DOWNWARD is
not. The way folks have been dealing with this is something like this after
the #includes:
/* Redefine STACK_GROWS_DOWNWARD in terms of 0 or 1. */
#ifdef STACK_GROWS_DOWNWARD
# undef STACK_GROWS_DOWNWARD
# define STACK_GROWS_DOWNWARD 1
#else
# define STACK_GROWS_DOWNWARD 0
#endif
With that in place you can change the test into the more desirable
if (ARGS_GROW_DOWNWARD !STACK_GROWS_DOWNWARD)
diff --git a/gcc/expr.c b/gcc/expr.c
index 25aa11f..712fa0b 100644
--- a/gcc/expr.c
+++ b/gcc/expr.c
@@ -4121,12 +4121,35 @@ emit_single_push_insn (machine_mode mode, rtx x, tree
type)
}
#endif
+/* If reading SIZE bytes from X will end up reading from
+ Y return the number of bytes that overlap. Return -1
+ if there is no overlap or -2 if we can't determing
Re: [PATCH][expr.c] PR 65358 Avoid clobbering partial argument during sibcall
On 05/11/2015 03:28 AM, Kyrill Tkachov wrote:
The more I think about this, the more I think it's an ugly can of
worms and maybe we should just disable sibcalls for partial
arguments. I doubt it's a big performance issue in general.
We already have quite a bit of code in calls.c to detect cases with
partial argument overlap for the
explicit purpose of allowing sibcalls when partial arguments occur in
the general case. However, that
code only detects when a partial argument overlaps with other arguments
in a call. In this PR the
partial argument overlaps with itself. It would be a shame to disable
sibcalls for all partial arguments
when there is already infrastructure in place to handle them.
I didn't even realize we had support for partial arguments in sibcalls.
Ah, Kazu added that in 2005, I totally missed it. I probably would
have suggested failing the sibcall for those cases back then too...
Is there any way to re-use that infrastructure to deal with the case at
hand?
In addition to the argument/stack direction stuff, I've been pondering
the stack/frame/arg pointer issues. Your approach assumes that the
incoming and outgoing areas are always referenced off the same base
register. If they aren't, then the routine returns no overlap.
But we'd need to consider the case where we have a reference to the
arg or frame pointer which later gets rewritten into a stack pointer
relative address.
Is it too late at the point were you do the checks to reject the
sibling call? If not, then maybe the overlap routine should return a
tri-state. No overlap, overlap, don't know. The last would be used
when the two addresses use a different register.
Ok, here is my attempt at that. The overlap functions returns -2 when it
cannot staticall compare the
two pointers (i.e. when the base registers are different) and the caller
then disables sibcalls.
The code in calls.c that calls this code will undo any emitted
instructions in the meantime if sibcall
optimisation fails. This required me to change the type of
emit_push_insn to bool and add an extra
parameter, so this patch touches a bit more code than the original version.
Bootstrapped on x86_64 and tested on arm. The testcase in this PR still
performs a sibcall correctly on arm.
What do you think of this?
Thanks,
Kyrill
2015-05-11 Kyrylo Tkachov kyrylo.tkac...@arm.com
PR target/65358
* expr.c (memory_load_overlap): New function.
(emit_push_insn): When pushing partial args to the stack would
clobber the register part load the overlapping part into a pseudo
and put it into the hard reg after pushing. Change return type
to bool. Add bool argument.
* expr.h (emit_push_insn): Change return type to bool.
Add bool argument.
* calls.c (expand_call): Cancel sibcall optimisation when encountering
partial argument on targets with ARGS_GROW_DOWNWARD and
!STACK_GROWS_DOWNWARD.
(emit_library_call_value_1): Update callsite of emit_push_insn.
(store_one_arg): Likewise.
2015-05-11 Honggyu Kim hong.gyu@lge.com
PR target/65358
* gcc.dg/pr65358.c: New test.
Jeff
expr.patch
commit 5b596f10846b6d3b143442a306801c8262d8b10a
Author: Kyrylo Tkachovkyrylo.tkac...@arm.com
Date: Wed Mar 18 13:42:37 2015 +
[expr.c] PR 65358 Avoid clobbering partial argument during sibcall
diff --git a/gcc/calls.c b/gcc/calls.c
index caa7d60..81ef2c9 100644
--- a/gcc/calls.c
+++ b/gcc/calls.c
@@ -3225,6 +3225,13 @@ expand_call (tree exp, rtx target, int ignore)
{
rtx_insn *before_arg = get_last_insn ();
+/* On targets with weird calling conventions (e.g. PA) it's
+ hard to ensure that all cases of argument overlap between
+ stack and registers work. Play it safe and bail out. */
+#if defined (ARGS_GROW_DOWNWARD) !defined (STACK_GROWS_DOWNWARD)
+ sibcall_failure = 1;
+ break;
+#endif
So we're trying to get away from this kind of conditional compilation.
Instead we want to write
if (ARGS_GROW_DOWNWARD !STACK_GROWS_DOWNWARD)
ARGS_GROW_DOWNWARD is already a testable value. But
STACK_GROWS_DOWNWARD is not. The way folks have been dealing with this
is something like this after the #includes:
/* Redefine STACK_GROWS_DOWNWARD in terms of 0 or 1. */
#ifdef STACK_GROWS_DOWNWARD
# undef STACK_GROWS_DOWNWARD
# define STACK_GROWS_DOWNWARD 1
#else
# define STACK_GROWS_DOWNWARD 0
#endif
With that in place you can change the test into the more desirable
if (ARGS_GROW_DOWNWARD !STACK_GROWS_DOWNWARD)
diff --git a/gcc/expr.c b/gcc/expr.c
index 25aa11f..712fa0b 100644
--- a/gcc/expr.c
+++ b/gcc/expr.c
@@ -4121,12 +4121,35 @@ emit_single_push_insn (machine_mode mode, rtx x, tree
type)
}
#endif
+/* If reading SIZE bytes from X will end up reading from
+ Y return the number of bytes that overlap. Return -1
+ if there is no overlap or -2 if we can't determing
s/determing/determine/
Re: [PATCH][expr.c] PR 65358 Avoid clobbering partial argument during sibcall
On 01/05/15 19:51, Jeff Law wrote:
On 04/28/2015 03:54 AM, Kyrill Tkachov wrote:
On 27/04/15 21:13, Jeff Law wrote:
On 04/21/2015 11:33 AM, Kyrill Tkachov wrote:
On 21/04/15 15:09, Jeff Law wrote:
On 04/21/2015 02:30 AM, Kyrill Tkachov wrote:
From reading config/stormy16/stormy-abi it seems to me that we
don't
pass arguments partially in stormy16, so this code would never be
called
there. That leaves pa as the potential problematic target.
I don't suppose there's an easy way to test on pa? My checkout of
binutils
doesn't seem to include a sim target for it.
No simulator, no machines in the testfarm, the box I had access to via
parisc-linux.org seems dead and my ancient PA overheats well before a
bootstrap could complete. I often regret knowing about the backwards
way many things were done on the PA because it makes me think about
cases that only matter on dead architectures.
So what should be the action plan here? I can't add an assert on
positive result as a negative result is valid.
We want to catch the case where this would cause trouble on
pa, or change the patch until we're confident that it's fine
for pa.
That being said, reading the documentation of STACK_GROWS_UPWARD
and ARGS_GROW_DOWNWARD I'm having a hard time visualising a case
where this would cause trouble on pa.
Is the problem that in the function:
+/* Add SIZE to X and check whether it's greater than Y.
+ If it is, return the constant amount by which it's greater or
smaller.
+ If the two are not statically comparable (for example, X and Y
contain
+ different registers) return -1. This is used in expand_push_insn to
+ figure out if reading SIZE bytes from location X will end up reading
from
+ location Y. */
+static int
+memory_load_overlap (rtx x, rtx y, HOST_WIDE_INT size)
+{
+ rtx tmp = plus_constant (Pmode, x, size);
+ rtx sub = simplify_gen_binary (MINUS, Pmode, tmp, y);
+
+ if (!CONST_INT_P (sub))
+return -1;
+
+ return INTVAL (sub);
+}
for ARGS_GROW_DOWNWARD we would be reading 'backwards' from x,
so the function should something like the following?
So I had to go back and compile some simple examples.
References to outgoing arguments will be SP relative. References to the
incoming arguments will be ARGP relative. And that brings me to the
another issue. Isn't X in this context the incoming argument slot and
the destination an outgoing argument slot?
If so, the approach of memory_load_overlap simply won't work on a target
with calling conventions like the PA. And you might really want to
consider punting for these kind of calling conventions
Ok, thanks for the guidance.
How about this? This patch disables sibcall optimisation when
encountering a partial argument when ARGS_GROW_DOWNWARD
!STACK_GROWS_DOWNWARD.
Hopefully this shouldn't harm codegen on parisc if, as you say, it's
rare to have
partial arguments anyway on PA due to the large number of argument regs.
I tested this on arm and bootstrapped on x86_64.
I am now going through the process of getting access to a Debian PA
machine to
give it a test there (thanks Dave!)
Ok if testing comes clean?
Thanks,
Kyrill
2015-04-28 Kyrylo Tkachov kyrylo.tkac...@arm.com
PR target/65358
* calls.c (expand_call): Cancel sibcall optimisation when encountering
partial argument on targets with ARGS_GROW_DOWNWARD and
!STACK_GROWS_DOWNWARD.
* expr.c (memory_load_overlap): New function.
(emit_push_insn): When pushing partial args to the stack would
clobber the register part load the overlapping part into a pseudo
and put it into the hard reg after pushing.
2015-04-28 Honggyu Kim hong.gyu@lge.com
PR target/65358
* gcc.dg/pr65358.c: New test.
The more I think about this, the more I think it's an ugly can of worms and
maybe we should just disable sibcalls for partial arguments. I doubt it's a
big performance issue in general.
We already have quite a bit of code in calls.c to detect cases with partial
argument overlap for the
explicit purpose of allowing sibcalls when partial arguments occur in the
general case. However, that
code only detects when a partial argument overlaps with other arguments in a
call. In this PR the
partial argument overlaps with itself. It would be a shame to disable sibcalls
for all partial arguments
when there is already infrastructure in place to handle them.
In addition to the argument/stack direction stuff, I've been pondering the stack/frame/arg pointer issues. Your approach assumes that the incoming and outgoing areas are always referenced off the same base register. If they aren't, then
the routine returns no overlap.
But we'd need to consider the case where we have a reference to the arg or
frame pointer which later gets rewritten into a stack pointer relative address.
Is it too late at the point were you do the checks to reject the sibling call? If not, then maybe the overlap routine should return a tri-state. No overlap, overlap, don't
Re: [PATCH][expr.c] PR 65358 Avoid clobbering partial argument during sibcall
On 2015-04-27 9:16 AM, John David Anglin wrote: Hi Dave, Would it be possible for you to test this patch on a 64-bit hppa or at least bootstrap it? https://gcc.gnu.org/ml/gcc-patches/2015-04/msg01288.html I started a build and test with your patch on hppa64-hp-hpux11.11 this morning. The patch didn't cause any regressions on hppa2.0w-hp-hpux11.11 and hppa64-hp-hpux11.11. Dave -- John David Anglin dave.ang...@bell.net
Re: [PATCH][expr.c] PR 65358 Avoid clobbering partial argument during sibcall
On 04/28/2015 03:54 AM, Kyrill Tkachov wrote:
On 27/04/15 21:13, Jeff Law wrote:
On 04/21/2015 11:33 AM, Kyrill Tkachov wrote:
On 21/04/15 15:09, Jeff Law wrote:
On 04/21/2015 02:30 AM, Kyrill Tkachov wrote:
From reading config/stormy16/stormy-abi it seems to me that we
don't
pass arguments partially in stormy16, so this code would never be
called
there. That leaves pa as the potential problematic target.
I don't suppose there's an easy way to test on pa? My checkout of
binutils
doesn't seem to include a sim target for it.
No simulator, no machines in the testfarm, the box I had access to via
parisc-linux.org seems dead and my ancient PA overheats well before a
bootstrap could complete. I often regret knowing about the backwards
way many things were done on the PA because it makes me think about
cases that only matter on dead architectures.
So what should be the action plan here? I can't add an assert on
positive result as a negative result is valid.
We want to catch the case where this would cause trouble on
pa, or change the patch until we're confident that it's fine
for pa.
That being said, reading the documentation of STACK_GROWS_UPWARD
and ARGS_GROW_DOWNWARD I'm having a hard time visualising a case
where this would cause trouble on pa.
Is the problem that in the function:
+/* Add SIZE to X and check whether it's greater than Y.
+ If it is, return the constant amount by which it's greater or
smaller.
+ If the two are not statically comparable (for example, X and Y
contain
+ different registers) return -1. This is used in expand_push_insn to
+ figure out if reading SIZE bytes from location X will end up reading
from
+ location Y. */
+static int
+memory_load_overlap (rtx x, rtx y, HOST_WIDE_INT size)
+{
+ rtx tmp = plus_constant (Pmode, x, size);
+ rtx sub = simplify_gen_binary (MINUS, Pmode, tmp, y);
+
+ if (!CONST_INT_P (sub))
+return -1;
+
+ return INTVAL (sub);
+}
for ARGS_GROW_DOWNWARD we would be reading 'backwards' from x,
so the function should something like the following?
So I had to go back and compile some simple examples.
References to outgoing arguments will be SP relative. References to the
incoming arguments will be ARGP relative. And that brings me to the
another issue. Isn't X in this context the incoming argument slot and
the destination an outgoing argument slot?
If so, the approach of memory_load_overlap simply won't work on a target
with calling conventions like the PA. And you might really want to
consider punting for these kind of calling conventions
Ok, thanks for the guidance.
How about this? This patch disables sibcall optimisation when
encountering a partial argument when ARGS_GROW_DOWNWARD
!STACK_GROWS_DOWNWARD.
Hopefully this shouldn't harm codegen on parisc if, as you say, it's
rare to have
partial arguments anyway on PA due to the large number of argument regs.
I tested this on arm and bootstrapped on x86_64.
I am now going through the process of getting access to a Debian PA
machine to
give it a test there (thanks Dave!)
Ok if testing comes clean?
Thanks,
Kyrill
2015-04-28 Kyrylo Tkachov kyrylo.tkac...@arm.com
PR target/65358
* calls.c (expand_call): Cancel sibcall optimisation when encountering
partial argument on targets with ARGS_GROW_DOWNWARD and
!STACK_GROWS_DOWNWARD.
* expr.c (memory_load_overlap): New function.
(emit_push_insn): When pushing partial args to the stack would
clobber the register part load the overlapping part into a pseudo
and put it into the hard reg after pushing.
2015-04-28 Honggyu Kim hong.gyu@lge.com
PR target/65358
* gcc.dg/pr65358.c: New test.
The more I think about this, the more I think it's an ugly can of worms
and maybe we should just disable sibcalls for partial arguments. I
doubt it's a big performance issue in general.
In addition to the argument/stack direction stuff, I've been pondering
the stack/frame/arg pointer issues. Your approach assumes that the
incoming and outgoing areas are always referenced off the same base
register. If they aren't, then the routine returns no overlap.
But we'd need to consider the case where we have a reference to the arg
or frame pointer which later gets rewritten into a stack pointer
relative address.
Is it too late at the point were you do the checks to reject the sibling
call? If not, then maybe the overlap routine should return a tri-state.
No overlap, overlap, don't know. The last would be used when the two
addresses use a different register.
Jeff
Re: [PATCH][expr.c] PR 65358 Avoid clobbering partial argument during sibcall
On 28/04/15 10:54, Kyrill Tkachov wrote:
On 27/04/15 21:13, Jeff Law wrote:
On 04/21/2015 11:33 AM, Kyrill Tkachov wrote:
On 21/04/15 15:09, Jeff Law wrote:
On 04/21/2015 02:30 AM, Kyrill Tkachov wrote:
From reading config/stormy16/stormy-abi it seems to me that we don't
pass arguments partially in stormy16, so this code would never be called
there. That leaves pa as the potential problematic target.
I don't suppose there's an easy way to test on pa? My checkout of
binutils
doesn't seem to include a sim target for it.
No simulator, no machines in the testfarm, the box I had access to via
parisc-linux.org seems dead and my ancient PA overheats well before a
bootstrap could complete. I often regret knowing about the backwards
way many things were done on the PA because it makes me think about
cases that only matter on dead architectures.
So what should be the action plan here? I can't add an assert on
positive result as a negative result is valid.
We want to catch the case where this would cause trouble on
pa, or change the patch until we're confident that it's fine
for pa.
That being said, reading the documentation of STACK_GROWS_UPWARD
and ARGS_GROW_DOWNWARD I'm having a hard time visualising a case
where this would cause trouble on pa.
Is the problem that in the function:
+/* Add SIZE to X and check whether it's greater than Y.
+ If it is, return the constant amount by which it's greater or smaller.
+ If the two are not statically comparable (for example, X and Y contain
+ different registers) return -1. This is used in expand_push_insn to
+ figure out if reading SIZE bytes from location X will end up reading
from
+ location Y. */
+static int
+memory_load_overlap (rtx x, rtx y, HOST_WIDE_INT size)
+{
+ rtx tmp = plus_constant (Pmode, x, size);
+ rtx sub = simplify_gen_binary (MINUS, Pmode, tmp, y);
+
+ if (!CONST_INT_P (sub))
+return -1;
+
+ return INTVAL (sub);
+}
for ARGS_GROW_DOWNWARD we would be reading 'backwards' from x,
so the function should something like the following?
So I had to go back and compile some simple examples.
References to outgoing arguments will be SP relative. References to the
incoming arguments will be ARGP relative. And that brings me to the
another issue. Isn't X in this context the incoming argument slot and
the destination an outgoing argument slot?
If so, the approach of memory_load_overlap simply won't work on a target
with calling conventions like the PA. And you might really want to
consider punting for these kind of calling conventions
Ok, thanks for the guidance.
How about this? This patch disables sibcall optimisation when
encountering a partial argument when ARGS_GROW_DOWNWARD
!STACK_GROWS_DOWNWARD.
Hopefully this shouldn't harm codegen on parisc if, as you say, it's rare to
have
partial arguments anyway on PA due to the large number of argument regs.
I tested this on arm and bootstrapped on x86_64.
I am now going through the process of getting access to a Debian PA machine to
give it a test there (thanks Dave!)
Ok if testing comes clean?
Hi Jeff,
So I got access to an hppa machine.
But as mentioned here https://gcc.gnu.org/ml/gcc/2015-04/msg00364.html
I don't think I can bootstrap and run a 64-bit pa testsuite.
I've verified that the compiler builds, but is there anything more I can
do in testing this patch?
The latest version is at
https://gcc.gnu.org/ml/gcc-patches/2015-04/msg01713.html
and disables sibcall optimisation on a target like pa when a partial argument
is encountered.
Thanks,
Kyrill
Thanks,
Kyrill
2015-04-28 Kyrylo Tkachov kyrylo.tkac...@arm.com
PR target/65358
* calls.c (expand_call): Cancel sibcall optimisation when encountering
partial argument on targets with ARGS_GROW_DOWNWARD and
!STACK_GROWS_DOWNWARD.
* expr.c (memory_load_overlap): New function.
(emit_push_insn): When pushing partial args to the stack would
clobber the register part load the overlapping part into a pseudo
and put it into the hard reg after pushing.
2015-04-28 Honggyu Kim hong.gyu@lge.com
PR target/65358
* gcc.dg/pr65358.c: New test.
If you hadn't already done the work, I'd suggest punting for any case
where we have args partially in regs and partially in memory :-)
More thoughts when I can get an hour or two to remind myself how all
this stuff works on the PA.
I will note that testing on the PA is unlikely to show anything simply
because it uses 8 parameter passing registers. So it's rare to pass
anything in memory at all. Even rarer to have something partially in
memory and partially in registers.
Jeff
Re: [PATCH][expr.c] PR 65358 Avoid clobbering partial argument during sibcall
On 27/04/15 21:13, Jeff Law wrote:
On 04/21/2015 11:33 AM, Kyrill Tkachov wrote:
On 21/04/15 15:09, Jeff Law wrote:
On 04/21/2015 02:30 AM, Kyrill Tkachov wrote:
From reading config/stormy16/stormy-abi it seems to me that we don't
pass arguments partially in stormy16, so this code would never be called
there. That leaves pa as the potential problematic target.
I don't suppose there's an easy way to test on pa? My checkout of
binutils
doesn't seem to include a sim target for it.
No simulator, no machines in the testfarm, the box I had access to via
parisc-linux.org seems dead and my ancient PA overheats well before a
bootstrap could complete. I often regret knowing about the backwards
way many things were done on the PA because it makes me think about
cases that only matter on dead architectures.
So what should be the action plan here? I can't add an assert on
positive result as a negative result is valid.
We want to catch the case where this would cause trouble on
pa, or change the patch until we're confident that it's fine
for pa.
That being said, reading the documentation of STACK_GROWS_UPWARD
and ARGS_GROW_DOWNWARD I'm having a hard time visualising a case
where this would cause trouble on pa.
Is the problem that in the function:
+/* Add SIZE to X and check whether it's greater than Y.
+ If it is, return the constant amount by which it's greater or smaller.
+ If the two are not statically comparable (for example, X and Y contain
+ different registers) return -1. This is used in expand_push_insn to
+ figure out if reading SIZE bytes from location X will end up reading
from
+ location Y. */
+static int
+memory_load_overlap (rtx x, rtx y, HOST_WIDE_INT size)
+{
+ rtx tmp = plus_constant (Pmode, x, size);
+ rtx sub = simplify_gen_binary (MINUS, Pmode, tmp, y);
+
+ if (!CONST_INT_P (sub))
+return -1;
+
+ return INTVAL (sub);
+}
for ARGS_GROW_DOWNWARD we would be reading 'backwards' from x,
so the function should something like the following?
So I had to go back and compile some simple examples.
References to outgoing arguments will be SP relative. References to the
incoming arguments will be ARGP relative. And that brings me to the
another issue. Isn't X in this context the incoming argument slot and
the destination an outgoing argument slot?
If so, the approach of memory_load_overlap simply won't work on a target
with calling conventions like the PA. And you might really want to
consider punting for these kind of calling conventions
Ok, thanks for the guidance.
How about this? This patch disables sibcall optimisation when
encountering a partial argument when ARGS_GROW_DOWNWARD
!STACK_GROWS_DOWNWARD.
Hopefully this shouldn't harm codegen on parisc if, as you say, it's rare to
have
partial arguments anyway on PA due to the large number of argument regs.
I tested this on arm and bootstrapped on x86_64.
I am now going through the process of getting access to a Debian PA machine to
give it a test there (thanks Dave!)
Ok if testing comes clean?
Thanks,
Kyrill
2015-04-28 Kyrylo Tkachov kyrylo.tkac...@arm.com
PR target/65358
* calls.c (expand_call): Cancel sibcall optimisation when encountering
partial argument on targets with ARGS_GROW_DOWNWARD and
!STACK_GROWS_DOWNWARD.
* expr.c (memory_load_overlap): New function.
(emit_push_insn): When pushing partial args to the stack would
clobber the register part load the overlapping part into a pseudo
and put it into the hard reg after pushing.
2015-04-28 Honggyu Kim hong.gyu@lge.com
PR target/65358
* gcc.dg/pr65358.c: New test.
If you hadn't already done the work, I'd suggest punting for any case
where we have args partially in regs and partially in memory :-)
More thoughts when I can get an hour or two to remind myself how all
this stuff works on the PA.
I will note that testing on the PA is unlikely to show anything simply
because it uses 8 parameter passing registers. So it's rare to pass
anything in memory at all. Even rarer to have something partially in
memory and partially in registers.
Jeff
commit 61beb521f63db2f7178e2c41e3747982ddcc8869
Author: Kyrylo Tkachov kyrylo.tkac...@arm.com
Date: Wed Mar 18 13:42:37 2015 +
[expr.c] PR 65358 Avoid clobbering partial argument during sibcall
diff --git a/gcc/calls.c b/gcc/calls.c
index 3be7ca5..8159232 100644
--- a/gcc/calls.c
+++ b/gcc/calls.c
@@ -3229,6 +3229,13 @@ expand_call (tree exp, rtx target, int ignore)
{
rtx_insn *before_arg = get_last_insn ();
+ /* On targets with weird calling conventions (e.g. PA) it's
+ hard to ensure that all cases of argument overlap between
+ stack and registers work. Play it safe and bail out. */
+#if defined (ARGS_GROW_DOWNWARD) !defined (STACK_GROWS_DOWNWARD)
+ sibcall_failure = 1;
+ break;
+#endif
if (store_one_arg (args[i], argblock, flags,
adjusted_args_size.var != 0,
reg_parm_stack_space)
diff
Re: [PATCH][expr.c] PR 65358 Avoid clobbering partial argument during sibcall
On 22/04/15 12:51, Kyrill Tkachov wrote:
On 21/04/15 18:33, Kyrill Tkachov wrote:
On 21/04/15 15:09, Jeff Law wrote:
On 04/21/2015 02:30 AM, Kyrill Tkachov wrote:
From reading config/stormy16/stormy-abi it seems to me that we don't
pass arguments partially in stormy16, so this code would never be called
there. That leaves pa as the potential problematic target.
I don't suppose there's an easy way to test on pa? My checkout of binutils
doesn't seem to include a sim target for it.
No simulator, no machines in the testfarm, the box I had access to via
parisc-linux.org seems dead and my ancient PA overheats well before a
bootstrap could complete. I often regret knowing about the backwards
way many things were done on the PA because it makes me think about
cases that only matter on dead architectures.
So what should be the action plan here? I can't add an assert on
positive result as a negative result is valid.
We want to catch the case where this would cause trouble on
pa, or change the patch until we're confident that it's fine
for pa.
That being said, reading the documentation of STACK_GROWS_UPWARD
and ARGS_GROW_DOWNWARD I'm having a hard time visualising a case
where this would cause trouble on pa.
Is the problem that in the function:
+/* Add SIZE to X and check whether it's greater than Y.
+ If it is, return the constant amount by which it's greater or smaller.
+ If the two are not statically comparable (for example, X and Y contain
+ different registers) return -1. This is used in expand_push_insn to
+ figure out if reading SIZE bytes from location X will end up reading from
+ location Y. */
+static int
+memory_load_overlap (rtx x, rtx y, HOST_WIDE_INT size)
+{
+ rtx tmp = plus_constant (Pmode, x, size);
+ rtx sub = simplify_gen_binary (MINUS, Pmode, tmp, y);
+
+ if (!CONST_INT_P (sub))
+return -1;
+
+ return INTVAL (sub);
+}
for ARGS_GROW_DOWNWARD we would be reading 'backwards' from x,
so the function should something like the following?
static int
memory_load_overlap (rtx x, rtx y, HOST_WIDE_INT size)
{
#ifdef ARGS_GROW_DOWNWARD
rtx tmp = plus_constant (Pmode, x, -size);
#else
rtx tmp = plus_constant (Pmode, x, size);
#endif
rtx sub = simplify_gen_binary (MINUS, Pmode, tmp, y);
if (!CONST_INT_P (sub))
return -1;
#ifdef ARGS_GROW_DOWNWARD
return INTVAL (-sub);
#else
return INTVAL (sub);
#endif
}
now, say for x == sp + 4, y == sp + 8, size == 16:
This would be a problematic case for arm, so this code on arm
(where ARGS_GROW_DOWNWARD is *not* defined) would return
12, which is the number of bytes that overlap.
On a target where ARGS_GROW_DOWNWARD is defined this would return
-20, meaning that no overlap occurs (because we read in the descending
direction from x, IIUC).
Hi Jeff,
Here's an attempt to make this more concrete.
Only the memory_load_overlap function has changed.
This time I tried to take into account the case when
ARGS_GROW_DOWNWARD.
Take the case where x == sp, y == sp + 8, size == 16.
For arm, this would return 8 as that is the number of bytes
that overlap. On pa, since ARGS_GROW_DOWNWARD is defined it
would return -1 as we're reading down from x rather than up
towards y.
In the case when x == sp + 8, y == sp, size == 16
This would return -1 on arm since we're reading upwards from x
and thefore no overlap would happen.
On pa, this would return 8, which I think is the right thing.
But again, I don't have access to any pa means of testing.
What do you think of this approach?
Hi Dave,
Would it be possible for you to test this patch on a 64-bit hppa
or at least bootstrap it?
https://gcc.gnu.org/ml/gcc-patches/2015-04/msg01288.html
There is a concern that it may potentially affect the passing of
complex arguments partially on the stack and partially in regs
on pa because of the way the args and stack grow on that target.
Unfortunately I don't have access to any hardware or simulators.
It would help a lot with getting this patch in.
Thanks,
Kyrill
Thanks,
Kyrill
P.S. I've included the testcase from Honggyu in the patch.
2015-04-22 Kyrylo Tkachov kyrylo.tkac...@arm.com
PR target/65358
* expr.c (memory_load_overlap): New function.
(emit_push_insn): When pushing partial args to the stack would
clobber the register part load the overlapping part into a pseudo
and put it into the hard reg after pushing.
2015-04-22 Honggyu Kim hong.gyu@lge.com
PR target/65358
* gcc.dg/pr65358.c: New test.
Thanks,
Kyrill
Jeff
Re: [PATCH][expr.c] PR 65358 Avoid clobbering partial argument during sibcall
On 04/21/2015 11:33 AM, Kyrill Tkachov wrote:
On 21/04/15 15:09, Jeff Law wrote:
On 04/21/2015 02:30 AM, Kyrill Tkachov wrote:
From reading config/stormy16/stormy-abi it seems to me that we don't
pass arguments partially in stormy16, so this code would never be called
there. That leaves pa as the potential problematic target.
I don't suppose there's an easy way to test on pa? My checkout of
binutils
doesn't seem to include a sim target for it.
No simulator, no machines in the testfarm, the box I had access to via
parisc-linux.org seems dead and my ancient PA overheats well before a
bootstrap could complete. I often regret knowing about the backwards
way many things were done on the PA because it makes me think about
cases that only matter on dead architectures.
So what should be the action plan here? I can't add an assert on
positive result as a negative result is valid.
We want to catch the case where this would cause trouble on
pa, or change the patch until we're confident that it's fine
for pa.
That being said, reading the documentation of STACK_GROWS_UPWARD
and ARGS_GROW_DOWNWARD I'm having a hard time visualising a case
where this would cause trouble on pa.
Is the problem that in the function:
+/* Add SIZE to X and check whether it's greater than Y.
+ If it is, return the constant amount by which it's greater or smaller.
+ If the two are not statically comparable (for example, X and Y contain
+ different registers) return -1. This is used in expand_push_insn to
+ figure out if reading SIZE bytes from location X will end up reading
from
+ location Y. */
+static int
+memory_load_overlap (rtx x, rtx y, HOST_WIDE_INT size)
+{
+ rtx tmp = plus_constant (Pmode, x, size);
+ rtx sub = simplify_gen_binary (MINUS, Pmode, tmp, y);
+
+ if (!CONST_INT_P (sub))
+return -1;
+
+ return INTVAL (sub);
+}
for ARGS_GROW_DOWNWARD we would be reading 'backwards' from x,
so the function should something like the following?
So I had to go back and compile some simple examples.
References to outgoing arguments will be SP relative. References to the
incoming arguments will be ARGP relative. And that brings me to the
another issue. Isn't X in this context the incoming argument slot and
the destination an outgoing argument slot?
If so, the approach of memory_load_overlap simply won't work on a target
with calling conventions like the PA. And you might really want to
consider punting for these kind of calling conventions
If you hadn't already done the work, I'd suggest punting for any case
where we have args partially in regs and partially in memory :-)
More thoughts when I can get an hour or two to remind myself how all
this stuff works on the PA.
I will note that testing on the PA is unlikely to show anything simply
because it uses 8 parameter passing registers. So it's rare to pass
anything in memory at all. Even rarer to have something partially in
memory and partially in registers.
Jeff
Re: [PATCH][expr.c] PR 65358 Avoid clobbering partial argument during sibcall
On 2015-04-27 6:12 AM, Kyrill Tkachov wrote:
On 22/04/15 12:51, Kyrill Tkachov wrote:
On 21/04/15 18:33, Kyrill Tkachov wrote:
On 21/04/15 15:09, Jeff Law wrote:
On 04/21/2015 02:30 AM, Kyrill Tkachov wrote:
From reading config/stormy16/stormy-abi it seems to me that we
don't
pass arguments partially in stormy16, so this code would never be
called
there. That leaves pa as the potential problematic target.
I don't suppose there's an easy way to test on pa? My checkout of
binutils
doesn't seem to include a sim target for it.
No simulator, no machines in the testfarm, the box I had access to via
parisc-linux.org seems dead and my ancient PA overheats well before a
bootstrap could complete. I often regret knowing about the backwards
way many things were done on the PA because it makes me think about
cases that only matter on dead architectures.
So what should be the action plan here? I can't add an assert on
positive result as a negative result is valid.
We want to catch the case where this would cause trouble on
pa, or change the patch until we're confident that it's fine
for pa.
That being said, reading the documentation of STACK_GROWS_UPWARD
and ARGS_GROW_DOWNWARD I'm having a hard time visualising a case
where this would cause trouble on pa.
Is the problem that in the function:
+/* Add SIZE to X and check whether it's greater than Y.
+ If it is, return the constant amount by which it's greater or
smaller.
+ If the two are not statically comparable (for example, X and Y
contain
+ different registers) return -1. This is used in
expand_push_insn to
+ figure out if reading SIZE bytes from location X will end up
reading from
+ location Y. */
+static int
+memory_load_overlap (rtx x, rtx y, HOST_WIDE_INT size)
+{
+ rtx tmp = plus_constant (Pmode, x, size);
+ rtx sub = simplify_gen_binary (MINUS, Pmode, tmp, y);
+
+ if (!CONST_INT_P (sub))
+return -1;
+
+ return INTVAL (sub);
+}
for ARGS_GROW_DOWNWARD we would be reading 'backwards' from x,
so the function should something like the following?
static int
memory_load_overlap (rtx x, rtx y, HOST_WIDE_INT size)
{
#ifdef ARGS_GROW_DOWNWARD
rtx tmp = plus_constant (Pmode, x, -size);
#else
rtx tmp = plus_constant (Pmode, x, size);
#endif
rtx sub = simplify_gen_binary (MINUS, Pmode, tmp, y);
if (!CONST_INT_P (sub))
return -1;
#ifdef ARGS_GROW_DOWNWARD
return INTVAL (-sub);
#else
return INTVAL (sub);
#endif
}
now, say for x == sp + 4, y == sp + 8, size == 16:
This would be a problematic case for arm, so this code on arm
(where ARGS_GROW_DOWNWARD is *not* defined) would return
12, which is the number of bytes that overlap.
On a target where ARGS_GROW_DOWNWARD is defined this would return
-20, meaning that no overlap occurs (because we read in the descending
direction from x, IIUC).
Hi Jeff,
Here's an attempt to make this more concrete.
Only the memory_load_overlap function has changed.
This time I tried to take into account the case when
ARGS_GROW_DOWNWARD.
Take the case where x == sp, y == sp + 8, size == 16.
For arm, this would return 8 as that is the number of bytes
that overlap. On pa, since ARGS_GROW_DOWNWARD is defined it
would return -1 as we're reading down from x rather than up
towards y.
In the case when x == sp + 8, y == sp, size == 16
This would return -1 on arm since we're reading upwards from x
and thefore no overlap would happen.
On pa, this would return 8, which I think is the right thing.
But again, I don't have access to any pa means of testing.
What do you think of this approach?
Hi Dave,
Would it be possible for you to test this patch on a 64-bit hppa
or at least bootstrap it?
https://gcc.gnu.org/ml/gcc-patches/2015-04/msg01288.html
I started a build and test with your patch on hppa64-hp-hpux11.11 this
morning.
There is a concern that it may potentially affect the passing of
complex arguments partially on the stack and partially in regs
on pa because of the way the args and stack grow on that target.
Unfortunately I don't have access to any hardware or simulators.
It would help a lot with getting this patch in.
If you write to linux-par...@vger.kernel.org, arrangements can be made for
an account on a Debian parisc linux machine for development testing.
Helge Deller has arranged for some new machines since we took over the
Debian buildd infrastructure for parisc. More info is here:
https://parisc.wiki.kernel.org/index.php/Main_Page
Thanks,
Kyrill
Thanks,
Kyrill
P.S. I've included the testcase from Honggyu in the patch.
2015-04-22 Kyrylo Tkachov kyrylo.tkac...@arm.com
PR target/65358
* expr.c (memory_load_overlap): New function.
(emit_push_insn): When pushing partial args to the stack would
clobber the register part load the overlapping part into a pseudo
and put it into the hard reg after pushing.
2015-04-22 Honggyu Kim hong.gyu@lge.com
PR target/65358
* gcc.dg/pr65358.c: New test.
Re: [PATCH][expr.c] PR 65358 Avoid clobbering partial argument during sibcall
On 21/04/15 18:33, Kyrill Tkachov wrote:
On 21/04/15 15:09, Jeff Law wrote:
On 04/21/2015 02:30 AM, Kyrill Tkachov wrote:
From reading config/stormy16/stormy-abi it seems to me that we don't
pass arguments partially in stormy16, so this code would never be called
there. That leaves pa as the potential problematic target.
I don't suppose there's an easy way to test on pa? My checkout of binutils
doesn't seem to include a sim target for it.
No simulator, no machines in the testfarm, the box I had access to via
parisc-linux.org seems dead and my ancient PA overheats well before a
bootstrap could complete. I often regret knowing about the backwards
way many things were done on the PA because it makes me think about
cases that only matter on dead architectures.
So what should be the action plan here? I can't add an assert on
positive result as a negative result is valid.
We want to catch the case where this would cause trouble on
pa, or change the patch until we're confident that it's fine
for pa.
That being said, reading the documentation of STACK_GROWS_UPWARD
and ARGS_GROW_DOWNWARD I'm having a hard time visualising a case
where this would cause trouble on pa.
Is the problem that in the function:
+/* Add SIZE to X and check whether it's greater than Y.
+ If it is, return the constant amount by which it's greater or smaller.
+ If the two are not statically comparable (for example, X and Y contain
+ different registers) return -1. This is used in expand_push_insn to
+ figure out if reading SIZE bytes from location X will end up reading from
+ location Y. */
+static int
+memory_load_overlap (rtx x, rtx y, HOST_WIDE_INT size)
+{
+ rtx tmp = plus_constant (Pmode, x, size);
+ rtx sub = simplify_gen_binary (MINUS, Pmode, tmp, y);
+
+ if (!CONST_INT_P (sub))
+return -1;
+
+ return INTVAL (sub);
+}
for ARGS_GROW_DOWNWARD we would be reading 'backwards' from x,
so the function should something like the following?
static int
memory_load_overlap (rtx x, rtx y, HOST_WIDE_INT size)
{
#ifdef ARGS_GROW_DOWNWARD
rtx tmp = plus_constant (Pmode, x, -size);
#else
rtx tmp = plus_constant (Pmode, x, size);
#endif
rtx sub = simplify_gen_binary (MINUS, Pmode, tmp, y);
if (!CONST_INT_P (sub))
return -1;
#ifdef ARGS_GROW_DOWNWARD
return INTVAL (-sub);
#else
return INTVAL (sub);
#endif
}
now, say for x == sp + 4, y == sp + 8, size == 16:
This would be a problematic case for arm, so this code on arm
(where ARGS_GROW_DOWNWARD is *not* defined) would return
12, which is the number of bytes that overlap.
On a target where ARGS_GROW_DOWNWARD is defined this would return
-20, meaning that no overlap occurs (because we read in the descending
direction from x, IIUC).
Hi Jeff,
Here's an attempt to make this more concrete.
Only the memory_load_overlap function has changed.
This time I tried to take into account the case when
ARGS_GROW_DOWNWARD.
Take the case where x == sp, y == sp + 8, size == 16.
For arm, this would return 8 as that is the number of bytes
that overlap. On pa, since ARGS_GROW_DOWNWARD is defined it
would return -1 as we're reading down from x rather than up
towards y.
In the case when x == sp + 8, y == sp, size == 16
This would return -1 on arm since we're reading upwards from x
and thefore no overlap would happen.
On pa, this would return 8, which I think is the right thing.
But again, I don't have access to any pa means of testing.
What do you think of this approach?
Thanks,
Kyrill
P.S. I've included the testcase from Honggyu in the patch.
2015-04-22 Kyrylo Tkachov kyrylo.tkac...@arm.com
PR target/65358
* expr.c (memory_load_overlap): New function.
(emit_push_insn): When pushing partial args to the stack would
clobber the register part load the overlapping part into a pseudo
and put it into the hard reg after pushing.
2015-04-22 Honggyu Kim hong.gyu@lge.com
PR target/65358
* gcc.dg/pr65358.c: New test.
Thanks,
Kyrill
Jeff
commit 39c9cb0bff1088cffaf31208b9a735d2bc0c505a
Author: Kyrylo Tkachov kyrylo.tkac...@arm.com
Date: Wed Mar 18 13:42:37 2015 +
[expr.c] PR 65358 Avoid clobbering partial argument during sibcall
diff --git a/gcc/expr.c b/gcc/expr.c
index 530a944..ccf94e0 100644
--- a/gcc/expr.c
+++ b/gcc/expr.c
@@ -4121,6 +4121,36 @@ emit_single_push_insn (machine_mode mode, rtx x, tree type)
}
#endif
+/* If reading SIZE bytes from X will end up reading from
+ Y return the number of bytes that overlap. Return -1
+ in all other cases. */
+
+static int
+memory_load_overlap (rtx x, rtx y, HOST_WIDE_INT size)
+{
+ rtx tmp = plus_constant (Pmode, x,
+#ifdef ARGS_GROW_DOWNWARD
+ -size);
+#else
+ size);
+#endif
+
+
+ rtx sub = simplify_gen_binary (MINUS, Pmode, tmp, y);
+
+ if (!CONST_INT_P (sub))
+return -1;
+
+ HOST_WIDE_INT val =
+#ifdef ARGS_GROW_DOWNWARD
+-INTVAL (sub);
+#else
+ INTVAL (sub);
+#endif
+
+ return IN_RANGE (val, 1, size) ? val : -1;
+}
+
Re: [PATCH][expr.c] PR 65358 Avoid clobbering partial argument during sibcall
On 21/04/15 15:09, Jeff Law wrote:
On 04/21/2015 02:30 AM, Kyrill Tkachov wrote:
From reading config/stormy16/stormy-abi it seems to me that we don't
pass arguments partially in stormy16, so this code would never be called
there. That leaves pa as the potential problematic target.
I don't suppose there's an easy way to test on pa? My checkout of binutils
doesn't seem to include a sim target for it.
No simulator, no machines in the testfarm, the box I had access to via
parisc-linux.org seems dead and my ancient PA overheats well before a
bootstrap could complete. I often regret knowing about the backwards
way many things were done on the PA because it makes me think about
cases that only matter on dead architectures.
So what should be the action plan here? I can't add an assert on
positive result as a negative result is valid.
We want to catch the case where this would cause trouble on
pa, or change the patch until we're confident that it's fine
for pa.
That being said, reading the documentation of STACK_GROWS_UPWARD
and ARGS_GROW_DOWNWARD I'm having a hard time visualising a case
where this would cause trouble on pa.
Is the problem that in the function:
+/* Add SIZE to X and check whether it's greater than Y.
+ If it is, return the constant amount by which it's greater or smaller.
+ If the two are not statically comparable (for example, X and Y contain
+ different registers) return -1. This is used in expand_push_insn to
+ figure out if reading SIZE bytes from location X will end up reading from
+ location Y. */
+static int
+memory_load_overlap (rtx x, rtx y, HOST_WIDE_INT size)
+{
+ rtx tmp = plus_constant (Pmode, x, size);
+ rtx sub = simplify_gen_binary (MINUS, Pmode, tmp, y);
+
+ if (!CONST_INT_P (sub))
+return -1;
+
+ return INTVAL (sub);
+}
for ARGS_GROW_DOWNWARD we would be reading 'backwards' from x,
so the function should something like the following?
static int
memory_load_overlap (rtx x, rtx y, HOST_WIDE_INT size)
{
#ifdef ARGS_GROW_DOWNWARD
rtx tmp = plus_constant (Pmode, x, -size);
#else
rtx tmp = plus_constant (Pmode, x, size);
#endif
rtx sub = simplify_gen_binary (MINUS, Pmode, tmp, y);
if (!CONST_INT_P (sub))
return -1;
#ifdef ARGS_GROW_DOWNWARD
return INTVAL (-sub);
#else
return INTVAL (sub);
#endif
}
now, say for x == sp + 4, y == sp + 8, size == 16:
This would be a problematic case for arm, so this code on arm
(where ARGS_GROW_DOWNWARD is *not* defined) would return
12, which is the number of bytes that overlap.
On a target where ARGS_GROW_DOWNWARD is defined this would return
-20, meaning that no overlap occurs (because we read in the descending
direction from x, IIUC).
Thanks,
Kyrill
Jeff
Re: [PATCH][expr.c] PR 65358 Avoid clobbering partial argument during sibcall
On 20/04/15 19:02, Jeff Law wrote:
On 04/20/2015 02:25 AM, Kyrill Tkachov wrote:
Hi Jeff,
Hmmm, so what happens if the difference is 0? I'd be a bit worried
about that case for the PA (for example).
So how about asserting that the INTVAL is = 0 prior to returning so
that we catch that case if it ever occurs?
INTVAL being = 0 is the case that I want to catch with this function.
INTVAL 0 is the usual case on leaf call optimisation. On arm, at least,
it means that x and y use the same base register (i.e. same stack frame)
but the offsets are such that reading SIZE bytes from X will not overlap
with Y, thus not requiring the workaround in this patch.
Thus, asserting that the result is positive is not right here.
What characteristic on pa makes this problematic? Is it the
STACK_GROWS_UPWARD?
Yea or more correctly that {STACK,FRAME}_GROWS_UPWARD and
ARGS_GROW_DOWNWARD. I think the stormy16 may have downward growing args
too.
Should I then extend this function to do something like:
HOST_WIDE_INT res = INTVAL (sub);
#ifndef STACK_GROWS_DOWNWARD
res = -res;
#endif
return res?
It certainly feels like something is needed for targets where growth is
in the opposite direction -- but my guess is that without a concrete
case that triggers on those targets (just the PA in 64 bit mode and
stormy?) we'll probably get it wrong in one way or another. Hence my
suggestion that we assert rather than try to handle it and silently
generate incorrect code in the process.
However, this function is expected to return negative numbers
when there is no overlap i.e. in the vast majority of cases when this
bug doesn't manifest. So asserting that it's positive is just
going to ICE at -O2 in almost any code.
From reading config/stormy16/stormy-abi it seems to me that we don't
pass arguments partially in stormy16, so this code would never be called
there. That leaves pa as the potential problematic target.
I don't suppose there's an easy way to test on pa? My checkout of binutils
doesn't seem to include a sim target for it.
Kyrill
Jeff
Re: [PATCH][expr.c] PR 65358 Avoid clobbering partial argument during sibcall
On 04/21/2015 02:30 AM, Kyrill Tkachov wrote: From reading config/stormy16/stormy-abi it seems to me that we don't pass arguments partially in stormy16, so this code would never be called there. That leaves pa as the potential problematic target. I don't suppose there's an easy way to test on pa? My checkout of binutils doesn't seem to include a sim target for it. No simulator, no machines in the testfarm, the box I had access to via parisc-linux.org seems dead and my ancient PA overheats well before a bootstrap could complete. I often regret knowing about the backwards way many things were done on the PA because it makes me think about cases that only matter on dead architectures. Jeff
Re: [PATCH][expr.c] PR 65358 Avoid clobbering partial argument during sibcall
Hi Jeff,
On 17/04/15 18:26, Jeff Law wrote:
On 03/19/2015 08:39 AM, Kyrill Tkachov wrote:
Hi all,
This patch fixes PR 65358. For details look at the excellent write-up
by Honggyu in bugzilla. The problem is that we're trying to pass a struct
partially on the stack and partially in regs during a tail-call
optimisation
but the struct we're passing is also a partial incoming arg though the
split
between stack and regs is different from its outgoing usage.
The emit_push_insn code ends up doing a block move for the on-stack part
but
ends up overwriting the part that needs to be loaded into regs.
My first thought was to just load the regs part first and then do the stack
part but that doesn't work as multiple comments in that function indicate
(the block move being expanded to movmem or other functions being one of
the
reasons).
My proposed solution is to detect when the overlap happens, find the
overlapping region and load it before the stack pushing into pseudos and
after the stack pushing is done move the overlapping values from the
pseudos
into the hard argument regs that they're supposed to go.
That way this new functionality should only ever be triggered when there's
the overlap in this PR (causing wrong-code) and shouldn't affect codegen
anywhere else.
Bootstrapped and tested on arm-none-linux-gnueabihf, aarch64-none-linux-gnu
and x86_64-linux-gnu.
According to the PR this appears at least as far back 4.6 so this isn't a
regression on the release branches, but it is a wrong-code bug.
I'll let Honggyu upstream the testcase separately
(https://gcc.gnu.org/ml/gcc-patches/2015-03/msg00984.html)
I'll be testing this on the 4.8 and 4.9 branches.
Thoughts on this approach?
Thanks,
Kyrill
2015-03-19 Kyrylo Tkachov kyrylo.tkac...@arm.com
PR middle-end/65358
* expr.c (memory_load_overlap): New function.
(emit_push_insn): When pushing partial args to the stack would
clobber the register part load the overlapping part into a pseudo
and put it into the hard reg after pushing.
expr.patch
commit 490c5f2074d76a2927afaea99e4dd0bacccb413c
Author: Kyrylo Tkachovkyrylo.tkac...@arm.com
Date: Wed Mar 18 13:42:37 2015 +
[expr.c] PR 65358 Avoid clobbering partial argument during sibcall
diff --git a/gcc/expr.c b/gcc/expr.c
index dc13a14..d3b9156 100644
--- a/gcc/expr.c
+++ b/gcc/expr.c
@@ -4121,6 +4121,25 @@ emit_single_push_insn (machine_mode mode, rtx x, tree
type)
}
#endif
+/* Add SIZE to X and check whether it's greater than Y.
+ If it is, return the constant amount by which it's greater or smaller.
+ If the two are not statically comparable (for example, X and Y contain
+ different registers) return -1. This is used in expand_push_insn to
+ figure out if reading SIZE bytes from location X will end up reading from
+ location Y. */
+
+static int
+memory_load_overlap (rtx x, rtx y, HOST_WIDE_INT size)
+{
+ rtx tmp = plus_constant (Pmode, x, size);
+ rtx sub = simplify_gen_binary (MINUS, Pmode, tmp, y);
+
+ if (!CONST_INT_P (sub))
+return -1;
+
+ return INTVAL (sub);
+}
Hmmm, so what happens if the difference is 0? I'd be a bit worried
about that case for the PA (for example).
So how about asserting that the INTVAL is = 0 prior to returning so
that we catch that case if it ever occurs?
INTVAL being = 0 is the case that I want to catch with this function.
INTVAL 0 is the usual case on leaf call optimisation. On arm, at least,
it means that x and y use the same base register (i.e. same stack frame)
but the offsets are such that reading SIZE bytes from X will not overlap
with Y, thus not requiring the workaround in this patch.
Thus, asserting that the result is positive is not right here.
What characteristic on pa makes this problematic? Is it the STACK_GROWS_UPWARD?
Should I then extend this function to do something like:
HOST_WIDE_INT res = INTVAL (sub);
#ifndef STACK_GROWS_DOWNWARD
res = -res;
#endif
return res?
OK for the trunk with the added assert. Please commit the testcase from
Honggyu at the same time you commit the patch.
Thanks, will do after the above is resolved.
Kyrill
Let's let it simmer for a while on the trunk before considering it to be
backported.
jeff
Re: [PATCH][expr.c] PR 65358 Avoid clobbering partial argument during sibcall
On 04/20/2015 02:25 AM, Kyrill Tkachov wrote:
Hi Jeff,
Hmmm, so what happens if the difference is 0? I'd be a bit worried
about that case for the PA (for example).
So how about asserting that the INTVAL is = 0 prior to returning so
that we catch that case if it ever occurs?
INTVAL being = 0 is the case that I want to catch with this function.
INTVAL 0 is the usual case on leaf call optimisation. On arm, at least,
it means that x and y use the same base register (i.e. same stack frame)
but the offsets are such that reading SIZE bytes from X will not overlap
with Y, thus not requiring the workaround in this patch.
Thus, asserting that the result is positive is not right here.
What characteristic on pa makes this problematic? Is it the
STACK_GROWS_UPWARD?
Yea or more correctly that {STACK,FRAME}_GROWS_UPWARD and
ARGS_GROW_DOWNWARD. I think the stormy16 may have downward growing args
too.
Should I then extend this function to do something like:
HOST_WIDE_INT res = INTVAL (sub);
#ifndef STACK_GROWS_DOWNWARD
res = -res;
#endif
return res?
It certainly feels like something is needed for targets where growth is
in the opposite direction -- but my guess is that without a concrete
case that triggers on those targets (just the PA in 64 bit mode and
stormy?) we'll probably get it wrong in one way or another. Hence my
suggestion that we assert rather than try to handle it and silently
generate incorrect code in the process.
Jeff
Re: [PATCH][expr.c] PR 65358 Avoid clobbering partial argument during sibcall
On 03/19/2015 08:39 AM, Kyrill Tkachov wrote:
Hi all,
This patch fixes PR 65358. For details look at the excellent write-up
by Honggyu in bugzilla. The problem is that we're trying to pass a struct
partially on the stack and partially in regs during a tail-call
optimisation
but the struct we're passing is also a partial incoming arg though the
split
between stack and regs is different from its outgoing usage.
The emit_push_insn code ends up doing a block move for the on-stack part
but
ends up overwriting the part that needs to be loaded into regs.
My first thought was to just load the regs part first and then do the stack
part but that doesn't work as multiple comments in that function indicate
(the block move being expanded to movmem or other functions being one of
the
reasons).
My proposed solution is to detect when the overlap happens, find the
overlapping region and load it before the stack pushing into pseudos and
after the stack pushing is done move the overlapping values from the
pseudos
into the hard argument regs that they're supposed to go.
That way this new functionality should only ever be triggered when there's
the overlap in this PR (causing wrong-code) and shouldn't affect codegen
anywhere else.
Bootstrapped and tested on arm-none-linux-gnueabihf, aarch64-none-linux-gnu
and x86_64-linux-gnu.
According to the PR this appears at least as far back 4.6 so this isn't a
regression on the release branches, but it is a wrong-code bug.
I'll let Honggyu upstream the testcase separately
(https://gcc.gnu.org/ml/gcc-patches/2015-03/msg00984.html)
I'll be testing this on the 4.8 and 4.9 branches.
Thoughts on this approach?
Thanks,
Kyrill
2015-03-19 Kyrylo Tkachov kyrylo.tkac...@arm.com
PR middle-end/65358
* expr.c (memory_load_overlap): New function.
(emit_push_insn): When pushing partial args to the stack would
clobber the register part load the overlapping part into a pseudo
and put it into the hard reg after pushing.
expr.patch
commit 490c5f2074d76a2927afaea99e4dd0bacccb413c
Author: Kyrylo Tkachovkyrylo.tkac...@arm.com
Date: Wed Mar 18 13:42:37 2015 +
[expr.c] PR 65358 Avoid clobbering partial argument during sibcall
diff --git a/gcc/expr.c b/gcc/expr.c
index dc13a14..d3b9156 100644
--- a/gcc/expr.c
+++ b/gcc/expr.c
@@ -4121,6 +4121,25 @@ emit_single_push_insn (machine_mode mode, rtx x, tree
type)
}
#endif
+/* Add SIZE to X and check whether it's greater than Y.
+ If it is, return the constant amount by which it's greater or smaller.
+ If the two are not statically comparable (for example, X and Y contain
+ different registers) return -1. This is used in expand_push_insn to
+ figure out if reading SIZE bytes from location X will end up reading from
+ location Y. */
+
+static int
+memory_load_overlap (rtx x, rtx y, HOST_WIDE_INT size)
+{
+ rtx tmp = plus_constant (Pmode, x, size);
+ rtx sub = simplify_gen_binary (MINUS, Pmode, tmp, y);
+
+ if (!CONST_INT_P (sub))
+return -1;
+
+ return INTVAL (sub);
+}
Hmmm, so what happens if the difference is 0? I'd be a bit worried
about that case for the PA (for example).
So how about asserting that the INTVAL is = 0 prior to returning so
that we catch that case if it ever occurs?
OK for the trunk with the added assert. Please commit the testcase from
Honggyu at the same time you commit the patch.
Let's let it simmer for a while on the trunk before considering it to be
backported.
jeff
Re: [PATCH][expr.c] PR 65358 Avoid clobbering partial argument during sibcall
Ping. https://gcc.gnu.org/ml/gcc-patches/2015-03/msg01014.html Jeff, could you help review this patch? Or could you point me to someone who can review this? I can't figure out from MAINTAINERS who should be in charge of this part of the compiler. Thanks, Kyrill On 19/03/15 14:39, Kyrill Tkachov wrote: Hi all, This patch fixes PR 65358. For details look at the excellent write-up by Honggyu in bugzilla. The problem is that we're trying to pass a struct partially on the stack and partially in regs during a tail-call optimisation but the struct we're passing is also a partial incoming arg though the split between stack and regs is different from its outgoing usage. The emit_push_insn code ends up doing a block move for the on-stack part but ends up overwriting the part that needs to be loaded into regs. My first thought was to just load the regs part first and then do the stack part but that doesn't work as multiple comments in that function indicate (the block move being expanded to movmem or other functions being one of the reasons). My proposed solution is to detect when the overlap happens, find the overlapping region and load it before the stack pushing into pseudos and after the stack pushing is done move the overlapping values from the pseudos into the hard argument regs that they're supposed to go. That way this new functionality should only ever be triggered when there's the overlap in this PR (causing wrong-code) and shouldn't affect codegen anywhere else. Bootstrapped and tested on arm-none-linux-gnueabihf, aarch64-none-linux-gnu and x86_64-linux-gnu. According to the PR this appears at least as far back 4.6 so this isn't a regression on the release branches, but it is a wrong-code bug. I'll let Honggyu upstream the testcase separately (https://gcc.gnu.org/ml/gcc-patches/2015-03/msg00984.html) I'll be testing this on the 4.8 and 4.9 branches. Thoughts on this approach? Thanks, Kyrill 2015-03-19 Kyrylo Tkachov kyrylo.tkac...@arm.com PR middle-end/65358 * expr.c (memory_load_overlap): New function. (emit_push_insn): When pushing partial args to the stack would clobber the register part load the overlapping part into a pseudo and put it into the hard reg after pushing.
Re: [PATCH][expr.c] PR 65358 Avoid clobbering partial argument during sibcall
On 04/13/2015 08:01 AM, Kyrill Tkachov wrote: Ping. https://gcc.gnu.org/ml/gcc-patches/2015-03/msg01014.html Jeff, could you help review this patch? Or could you point me to someone who can review this? I can't figure out from MAINTAINERS who should be in charge of this part of the compiler. It's in the queue of things to look at. It wasn't marked as a regression and thus I deferred it. With stage1 opening up we'll be working through the queue of deferred stuff shortly. jeff
Re: [PATCH][expr.c] PR 65358 Avoid clobbering partial argument during sibcall
On Thu, Mar 19, 2015 at 02:39:11PM +, Kyrill Tkachov wrote:
Hi all,
This patch fixes PR 65358. For details look at the excellent write-up
by Honggyu in bugzilla. The problem is that we're trying to pass a struct
partially on the stack and partially in regs during a tail-call optimisation
but the struct we're passing is also a partial incoming arg though the split
between stack and regs is different from its outgoing usage.
The emit_push_insn code ends up doing a block move for the on-stack part but
ends up overwriting the part that needs to be loaded into regs.
My first thought was to just load the regs part first and then do the stack
part but that doesn't work as multiple comments in that function indicate
(the block move being expanded to movmem or other functions being one of the
reasons).
My proposed solution is to detect when the overlap happens, find the
overlapping region and load it before the stack pushing into pseudos and
after the stack pushing is done move the overlapping values from the pseudos
into the hard argument regs that they're supposed to go.
That way this new functionality should only ever be triggered when there's
the overlap in this PR (causing wrong-code) and shouldn't affect codegen
anywhere else.
Bootstrapped and tested on arm-none-linux-gnueabihf, aarch64-none-linux-gnu
and x86_64-linux-gnu.
According to the PR this appears at least as far back 4.6 so this isn't a
regression on the release branches, but it is a wrong-code bug.
I'll let Honggyu upstream the testcase separately
(https://gcc.gnu.org/ml/gcc-patches/2015-03/msg00984.html)
I'll be testing this on the 4.8 and 4.9 branches.
Thoughts on this approach?
Thanks,
Kyrill
Hi, Kyrill
I have verified the generated assembly code and tested on the target board.
PR 65358 testcase works fine now with your patch.
https://gcc.gnu.org/ml/gcc-patches/2015-03/msg00984.html
Here is the generated assembly code of PR 65358:
foo:(without this patch)|(with this patch)
sub sp, sp, #8 |sub sp, sp, #8
mov r0, r1 |mov r0, r1
str lr, [sp, #-4]! |str lr, [sp, #-4]!
add ip, sp, #8 |mov r1, r2
(1) ldr lr, [sp, #16] |ldr lr, [sp, #16]
mov r1, r2 |mov r2, r3
str r3, [sp, #8]|ldr ip, [sp, #12]
(2) str lr, [sp, #12] |str r3, [sp, #8]
ldr lr, [sp], #4|str lr, [sp, #12]
ldmia ip, {r2, r3}|ldr lr, [sp], #4
add sp, sp, #8 |mov r3, ip
b bar |add sp, sp, #8
|b bar
One the left side(previous code), (1) loads p.killer, then (2) overwrites
p.victim value.
Until this point, p.victim is never copied anyway, which makes the
value disappear.
But this bug is clearly fixed with this patch as shown on the right side.
I have tested on x86_64 and got the working code regardless of having
this patch.
I appreciate your patch, Kyrill.
Honggyu
Re: [PATCH][expr.c] PR 65358 Avoid clobbering partial argument during sibcall
Ping. https://gcc.gnu.org/ml/gcc-patches/2015-03/msg01014.html Thanks, Kyrill On 19/03/15 14:39, Kyrill Tkachov wrote: Hi all, This patch fixes PR 65358. For details look at the excellent write-up by Honggyu in bugzilla. The problem is that we're trying to pass a struct partially on the stack and partially in regs during a tail-call optimisation but the struct we're passing is also a partial incoming arg though the split between stack and regs is different from its outgoing usage. The emit_push_insn code ends up doing a block move for the on-stack part but ends up overwriting the part that needs to be loaded into regs. My first thought was to just load the regs part first and then do the stack part but that doesn't work as multiple comments in that function indicate (the block move being expanded to movmem or other functions being one of the reasons). My proposed solution is to detect when the overlap happens, find the overlapping region and load it before the stack pushing into pseudos and after the stack pushing is done move the overlapping values from the pseudos into the hard argument regs that they're supposed to go. That way this new functionality should only ever be triggered when there's the overlap in this PR (causing wrong-code) and shouldn't affect codegen anywhere else. Bootstrapped and tested on arm-none-linux-gnueabihf, aarch64-none-linux-gnu and x86_64-linux-gnu. According to the PR this appears at least as far back 4.6 so this isn't a regression on the release branches, but it is a wrong-code bug. I'll let Honggyu upstream the testcase separately (https://gcc.gnu.org/ml/gcc-patches/2015-03/msg00984.html) After guidance from Jeff, I'll take this testcase in as well if this is approved. I'll be testing this on the 4.8 and 4.9 branches. Thoughts on this approach? Thanks, Kyrill 2015-03-19 Kyrylo Tkachov kyrylo.tkac...@arm.com PR middle-end/65358 * expr.c (memory_load_overlap): New function. (emit_push_insn): When pushing partial args to the stack would clobber the register part load the overlapping part into a pseudo and put it into the hard reg after pushing.
[PATCH][expr.c] PR 65358 Avoid clobbering partial argument during sibcall
Hi all,
This patch fixes PR 65358. For details look at the excellent write-up
by Honggyu in bugzilla. The problem is that we're trying to pass a struct
partially on the stack and partially in regs during a tail-call optimisation
but the struct we're passing is also a partial incoming arg though the split
between stack and regs is different from its outgoing usage.
The emit_push_insn code ends up doing a block move for the on-stack part but
ends up overwriting the part that needs to be loaded into regs.
My first thought was to just load the regs part first and then do the stack
part but that doesn't work as multiple comments in that function indicate
(the block move being expanded to movmem or other functions being one of the
reasons).
My proposed solution is to detect when the overlap happens, find the
overlapping region and load it before the stack pushing into pseudos and
after the stack pushing is done move the overlapping values from the pseudos
into the hard argument regs that they're supposed to go.
That way this new functionality should only ever be triggered when there's
the overlap in this PR (causing wrong-code) and shouldn't affect codegen
anywhere else.
Bootstrapped and tested on arm-none-linux-gnueabihf, aarch64-none-linux-gnu
and x86_64-linux-gnu.
According to the PR this appears at least as far back 4.6 so this isn't a
regression on the release branches, but it is a wrong-code bug.
I'll let Honggyu upstream the testcase separately
(https://gcc.gnu.org/ml/gcc-patches/2015-03/msg00984.html)
I'll be testing this on the 4.8 and 4.9 branches.
Thoughts on this approach?
Thanks,
Kyrill
2015-03-19 Kyrylo Tkachov kyrylo.tkac...@arm.com
PR middle-end/65358
* expr.c (memory_load_overlap): New function.
(emit_push_insn): When pushing partial args to the stack would
clobber the register part load the overlapping part into a pseudo
and put it into the hard reg after pushing.commit 490c5f2074d76a2927afaea99e4dd0bacccb413c
Author: Kyrylo Tkachov kyrylo.tkac...@arm.com
Date: Wed Mar 18 13:42:37 2015 +
[expr.c] PR 65358 Avoid clobbering partial argument during sibcall
diff --git a/gcc/expr.c b/gcc/expr.c
index dc13a14..d3b9156 100644
--- a/gcc/expr.c
+++ b/gcc/expr.c
@@ -4121,6 +4121,25 @@ emit_single_push_insn (machine_mode mode, rtx x, tree type)
}
#endif
+/* Add SIZE to X and check whether it's greater than Y.
+ If it is, return the constant amount by which it's greater or smaller.
+ If the two are not statically comparable (for example, X and Y contain
+ different registers) return -1. This is used in expand_push_insn to
+ figure out if reading SIZE bytes from location X will end up reading from
+ location Y. */
+
+static int
+memory_load_overlap (rtx x, rtx y, HOST_WIDE_INT size)
+{
+ rtx tmp = plus_constant (Pmode, x, size);
+ rtx sub = simplify_gen_binary (MINUS, Pmode, tmp, y);
+
+ if (!CONST_INT_P (sub))
+return -1;
+
+ return INTVAL (sub);
+}
+
/* Generate code to push X onto the stack, assuming it has mode MODE and
type TYPE.
MODE is redundant except when X is a CONST_INT (since they don't
@@ -4179,6 +4198,10 @@ emit_push_insn (rtx x, machine_mode mode, tree type, rtx size,
xinner = x;
+ int nregs = partial / UNITS_PER_WORD;
+ rtx *tmp_regs = NULL;
+ int overlapping = 0;
+
if (mode == BLKmode
|| (STRICT_ALIGNMENT align GET_MODE_ALIGNMENT (mode)))
{
@@ -4309,6 +4332,35 @@ emit_push_insn (rtx x, machine_mode mode, tree type, rtx size,
PARM_BOUNDARY. Assume the caller isn't lying. */
set_mem_align (target, align);
+ /* If part should go in registers and pushing to that part would
+ overwrite some of the values that need to go into regs, load the
+ overlapping values into temporary pseudos to be moved into the hard
+ regs at the end after the stack pushing has completed.
+ We cannot load them directly into the hard regs here because
+ they can be clobbered by the block move expansions.
+ See PR 65358. */
+
+ if (partial 0 reg != 0 mode == BLKmode
+ GET_CODE (reg) != PARALLEL)
+ {
+ overlapping = memory_load_overlap (XEXP (x, 0), temp, partial);
+ if (overlapping 0)
+ {
+ gcc_assert (overlapping % UNITS_PER_WORD == 0);
+ overlapping /= UNITS_PER_WORD;
+
+ tmp_regs = XALLOCAVEC (rtx, overlapping);
+
+ for (int i = 0; i overlapping; i++)
+ tmp_regs[i] = gen_reg_rtx (word_mode);
+
+ for (int i = 0; i overlapping; i++)
+ emit_move_insn (tmp_regs[i],
+operand_subword_force (target, i, mode));
+ }
+ else
+ overlapping = 0;
+ }
emit_block_move (target, xinner, size, BLOCK_OP_CALL_PARM);
}
}
@@ -4411,9 +4463,8 @@ emit_push_insn (rtx x, machine_mode mode, tree type, rtx size,
}
}
- /* If part should go in registers, copy that part
- into the appropriate registers. Do this now, at the end,
- since mem-to-mem copies above may do function
