On Thu, Nov 07, 2024 at 09:12:34AM +0100, Uros Bizjak wrote:
> On Thu, Nov 7, 2024 at 9:00 AM Jakub Jelinek <ja...@redhat.com> wrote:
> >
> > On Thu, Nov 07, 2024 at 08:47:34AM +0100, Uros Bizjak wrote:
> > > Maybe we should always recognize "redzone", even for targets without
> > > it. This is the way we recognize "cc" even for targets without CC reg
> > > (e.g. alpha). This would simplify the definition and processing - if
> > > the hook returns NULL_RTX (the default), then it (obviously) won't be
> > > added to the clobber list.
> >
> > Dunno, am open to that, but thought it would be just weird if one says
> > "redzone" on targets which don't have such a concept.
>
> Let's look at the situation with x86_32 and x86_64. The "redzone" for
> the former is just an afterthought, so we can safely say that it
> doesn't support it. So, the code that targets both targets (e.g. linux
> kernel) would (in a pedantic way) have to redefine many shared asm
> defines, one to have clobber and one without it. We don't want that,
> we want one definition and "let's compiler sort it out".
>
> For targets without clobber concept, well - don't add it to the
> clobber list if it is always ineffective. One *can* add "cc" to all
> alpha asms, but well.. ;)
Ok, here is a variant of the patch which just ignores "redzone" clobber if
it doesn't make sense.
2024-11-07 Jakub Jelinek <ja...@redhat.com>
gcc/
* target.def (redzone_clobber): New target hook.
* varasm.cc (decode_reg_name_and_count): Return -5 for
"redzone".
* cfgexpand.cc (expand_asm_stmt): Handle redzone clobber.
* config/i386/i386.h (struct machine_function): Add
asm_redzone_clobber_seen member.
* config/i386/i386.cc (ix86_compute_frame_layout): Don't
use red zone if cfun->machine->asm_redzone_clobber_seen.
(ix86_redzone_clobber): New function.
(TARGET_REDZONE_CLOBBER): Redefine.
* doc/extend.texi (Clobbers and Scratch Registers): Document
the "redzone" clobber.
* doc/tm.texi.in: Add @hook TARGET_REDZONE_CLOBBER.
* doc/tm.texi: Regenerate.
gcc/testsuite/
* gcc.dg/asm-redzone-1.c: New test.
* gcc.target/i386/asm-redzone-1.c: New test.
--- gcc/target.def.jj 2024-11-06 18:53:10.836843793 +0100
+++ gcc/target.def 2024-11-07 10:57:58.697898800 +0100
@@ -3376,6 +3376,16 @@ to be used.",
bool, (machine_mode mode),
NULL)
+DEFHOOK
+(redzone_clobber,
+ "Define this to return some RTL for the @code{redzone} @code{asm} clobber\n\
+if target has a red zone and wants to support the @code{redzone} clobber\n\
+or return NULL if the clobber should be ignored.\n\
+\n\
+The default is to ignore the @code{redzone} clobber.",
+ rtx, (),
+ NULL)
+
/* Support for named address spaces. */
#undef HOOK_PREFIX
#define HOOK_PREFIX "TARGET_ADDR_SPACE_"
--- gcc/varasm.cc.jj 2024-11-06 18:53:10.838843765 +0100
+++ gcc/varasm.cc 2024-11-07 10:55:46.858763724 +0100
@@ -965,9 +965,11 @@ set_user_assembler_name (tree decl, cons
/* Decode an `asm' spec for a declaration as a register name.
Return the register number, or -1 if nothing specified,
- or -2 if the ASMSPEC is not `cc' or `memory' and is not recognized,
+ or -2 if the ASMSPEC is not `cc' or `memory' or `redzone' and is not
+ recognized,
or -3 if ASMSPEC is `cc' and is not recognized,
- or -4 if ASMSPEC is `memory' and is not recognized.
+ or -4 if ASMSPEC is `memory' and is not recognized,
+ or -5 if ASMSPEC is `redzone' and is not recognized.
Accept an exact spelling or a decimal number.
Prefixes such as % are optional. */
@@ -1034,6 +1036,9 @@ decode_reg_name_and_count (const char *a
}
#endif /* ADDITIONAL_REGISTER_NAMES */
+ if (!strcmp (asmspec, "redzone"))
+ return -5;
+
if (!strcmp (asmspec, "memory"))
return -4;
--- gcc/cfgexpand.cc.jj 2024-11-06 18:53:10.803844259 +0100
+++ gcc/cfgexpand.cc 2024-11-07 11:00:16.212953571 +0100
@@ -3205,6 +3205,12 @@ expand_asm_stmt (gasm *stmt)
rtx x = gen_rtx_MEM (BLKmode, gen_rtx_SCRATCH (VOIDmode));
clobber_rvec.safe_push (x);
}
+ else if (j == -5)
+ {
+ if (targetm.redzone_clobber)
+ if (rtx x = targetm.redzone_clobber ())
+ clobber_rvec.safe_push (x);
+ }
else
{
/* Otherwise we should have -1 == empty string
--- gcc/config/i386/i386.h.jj 2024-11-06 18:53:10.807844203 +0100
+++ gcc/config/i386/i386.h 2024-11-07 10:55:46.904763076 +0100
@@ -2881,6 +2881,9 @@ struct GTY(()) machine_function {
/* True if red zone is used. */
BOOL_BITFIELD red_zone_used : 1;
+ /* True if inline asm with redzone clobber has been seen. */
+ BOOL_BITFIELD asm_redzone_clobber_seen : 1;
+
/* The largest alignment, in bytes, of stack slot actually used. */
unsigned int max_used_stack_alignment;
--- gcc/config/i386/i386.cc.jj 2024-11-06 18:53:10.807844203 +0100
+++ gcc/config/i386/i386.cc 2024-11-07 10:55:46.947762468 +0100
@@ -7171,6 +7171,7 @@ ix86_compute_frame_layout (void)
if (ix86_using_red_zone ()
&& crtl->sp_is_unchanging
&& crtl->is_leaf
+ && !cfun->machine->asm_redzone_clobber_seen
&& !ix86_pc_thunk_call_expanded
&& !ix86_current_function_calls_tls_descriptor)
{
@@ -26268,6 +26269,22 @@ ix86_mode_can_transfer_bits (machine_mod
return true;
}
+/* Implement TARGET_REDZONE_CLOBBER. */
+static rtx
+ix86_redzone_clobber ()
+{
+ cfun->machine->asm_redzone_clobber_seen = true;
+ if (ix86_using_red_zone ())
+ {
+ rtx base = plus_constant (Pmode, stack_pointer_rtx,
+ GEN_INT (-RED_ZONE_SIZE));
+ rtx mem = gen_rtx_MEM (BLKmode, base);
+ set_mem_size (mem, RED_ZONE_SIZE);
+ return mem;
+ }
+ return NULL_RTX;
+}
+
/* Target-specific selftests. */
#if CHECKING_P
@@ -27121,6 +27138,9 @@ ix86_libgcc_floating_mode_supported_p
#undef TARGET_MODE_CAN_TRANSFER_BITS
#define TARGET_MODE_CAN_TRANSFER_BITS ix86_mode_can_transfer_bits
+#undef TARGET_REDZONE_CLOBBER
+#define TARGET_REDZONE_CLOBBER ix86_redzone_clobber
+
static bool
ix86_libc_has_fast_function (int fcode ATTRIBUTE_UNUSED)
{
--- gcc/doc/extend.texi.jj 2024-11-06 18:53:10.826843934 +0100
+++ gcc/doc/extend.texi 2024-11-07 10:57:07.550622297 +0100
@@ -11827,7 +11827,7 @@ asm volatile ("movc3 %0, %1, %2"
: "r0", "r1", "r2", "r3", "r4", "r5", "memory");
@end example
-Also, there are two special clobber arguments:
+Also, there are three special clobber arguments:
@table @code
@item "cc"
@@ -11855,6 +11855,18 @@ Note that this clobber does not prevent
speculative reads past the @code{asm} statement. To prevent that, you need
processor-specific fence instructions.
+@item "redzone"
+The @code{"redzone"} clobber tells the compiler that the assembly code
+may write to the stack red zone, area below the stack pointer which on
+some architectures in some calling conventions is guaranteed not to be
+changed by signal handlers, interrupts or exceptions and so the compiler
+can store there temporaries in leaf functions. On targets which have
+no concept of the stack red zone, the clobber is ignored.
+It should be used e.g.@: in case the assembly code uses call instructions
+or pushes something to the stack without taking the red zone into account
+by subtracting red zone size from the stack pointer first and restoring
+it afterwards.
+
@end table
Flushing registers to memory has performance implications and may be
--- gcc/doc/tm.texi.in.jj 2024-11-06 18:53:10.833843835 +0100
+++ gcc/doc/tm.texi.in 2024-11-07 10:55:46.998761746 +0100
@@ -3464,6 +3464,8 @@ stack.
@hook TARGET_MODE_CAN_TRANSFER_BITS
+@hook TARGET_REDZONE_CLOBBER
+
@hook TARGET_TRANSLATE_MODE_ATTRIBUTE
@hook TARGET_SCALAR_MODE_SUPPORTED_P
--- gcc/doc/tm.texi.jj 2024-11-06 18:53:10.831843863 +0100
+++ gcc/doc/tm.texi 2024-11-07 10:55:47.008761605 +0100
@@ -4563,6 +4563,14 @@ The default is to assume modes with the
to be used.
@end deftypefn
+@deftypefn {Target Hook} rtx TARGET_REDZONE_CLOBBER ()
+Define this to return some RTL for the @code{redzone} @code{asm} clobber
+if target has a red zone and wants to support the @code{redzone} clobber
+or return NULL if the clobber should be ignored.
+
+The default is to ignore the @code{redzone} clobber.
+@end deftypefn
+
@deftypefn {Target Hook} machine_mode TARGET_TRANSLATE_MODE_ATTRIBUTE
(machine_mode @var{mode})
Define this hook if during mode attribute processing, the port should
translate machine_mode @var{mode} to another mode. For example, rs6000's
--- gcc/testsuite/gcc.dg/asm-redzone-1.c.jj 2024-11-07 11:07:52.873493855
+0100
+++ gcc/testsuite/gcc.dg/asm-redzone-1.c 2024-11-07 11:07:45.697595356
+0100
@@ -0,0 +1,8 @@
+/* { dg-do compile } */
+/* { dg-options "" } */
+
+void
+foo (void)
+{
+ asm ("" : : : "cc", "memory", "redzone");
+}
--- gcc/testsuite/gcc.target/i386/asm-redzone-1.c.jj 2024-11-07
10:55:47.018761463 +0100
+++ gcc/testsuite/gcc.target/i386/asm-redzone-1.c 2024-11-07
10:55:47.018761463 +0100
@@ -0,0 +1,38 @@
+/* { dg-do run { target lp64 } } */
+/* { dg-options "-O2" } */
+
+__attribute__((noipa)) int
+foo (void)
+{
+ int a = 1;
+ int b = 2;
+ int c = 3;
+ int d = 4;
+ int e = 5;
+ int f = 6;
+ int g = 7;
+ int h = 8;
+ int i = 9;
+ int j = 10;
+ int k = 11;
+ int l = 12;
+ int m = 13;
+ int n = 14;
+ asm volatile ("" : "+g" (a), "+g" (b), "+g" (c), "+g" (d), "+g" (e));
+ asm volatile ("" : "+g" (f), "+g" (g), "+g" (h), "+g" (i), "+g" (j));
+ asm volatile ("" : "+g" (k), "+g" (l), "+g" (m), "+g" (n));
+ asm volatile ("{pushq %%rax; pushq %%rax; popq %%rax; popq %%rax"
+ "|push rax;push rax;pop rax;pop rax}"
+ : : : "ax", "si", "di", "r10", "r11", "redzone");
+ asm volatile ("" : "+g" (a), "+g" (b), "+g" (c), "+g" (d), "+g" (e));
+ asm volatile ("" : "+g" (f), "+g" (g), "+g" (h), "+g" (i), "+g" (j));
+ asm volatile ("" : "+g" (k), "+g" (l), "+g" (m), "+g" (n));
+ return a + b + c + d + e + f + g + h + i + j + k + l + m + n;
+}
+
+int
+main ()
+{
+ if (foo () != 105)
+ __builtin_abort ();
+}
Jakub
