Re: Missed optimisation case - internal use of STCin
On 20 Apr 2014 13:19, Artur Skawina via Digitalmars-d digitalmars-d@puremagic.com wrote: On 04/20/14 03:00, Iain Buclaw via Digitalmars-d wrote: On 19 April 2014 17:10, Artur Skawina via Digitalmars-d digitalmars-d@puremagic.com wrote: On 04/19/14 16:21, Iain Buclaw via Digitalmars-d wrote: On 19 April 2014 14:33, Artur Skawina via Digitalmars-d digitalmars-d@puremagic.com wrote: On 04/19/14 14:37, Iain Buclaw via Digitalmars-d wrote: On 19 April 2014 13:02, Artur Skawina via Digitalmars-d digitalmars-d@puremagic.com wrote: On 04/19/14 13:03, Iain Buclaw via Digitalmars-d wrote: On Saturday, 19 April 2014 at 10:49:22 UTC, Iain Buclaw wrote: I'm currently testing out a GCC optimisation that allows you to set call argument flags. The current assumptions being: in parameters = Assume no escape, no clobber (read-only). ref parameters, classes and pointers = Assume worst case. default = Assume no escape. That should read: ref parameters, inout parameters, classes and pointers. The default of assuming no escape is an experiment - I may limit this to only scalar types, and parameters marked as 'scope' (So long as no one plans on deprecating it soon :) What does assume no escape actually mean? [The above list doesn't really make sense. W/o context, it's hard to even tell why, hence the question.] What I was wondering was things like whether that assume no escape property was transitive; if /locally/ escaping was disallowed, and to what extent. What does assume no escape mean at all? In your examples you're mentioning refs together with pointers, that would only make sense if no-escape were transitive -- but then treating all args as no-escape would be very wrong. I'm worried about a) invalid assumptions making it into GDC; b) certain valid assumptions making into GDC. The latter because it could mean that code that's incorrect, but still accepted by the other compilers could silently break when compiled with GDC. Invalid assumptions rarely make it into GDC. The testsuite is a good AFAICT what you're proposing *is* invalid. I can't be sure because it's not clear what that no-escape property means; that's why I asked about it twice already... Clearly, escaping objects reachable indirectly via function arguments is perfectly fine (eg string slicing), yet you wanted to treat args as no-escape by default. Not wanted - experimented. I could not think at the time a use case where a parameter could escape. And *I* have shown a very valid use case to *disprove myself*. I'm not sure of your continual persistence of bringing this up as this is no longer relevant to me. Other than Several reasons. First, I did not realize that you had changed your mind. It wouldn't be an experiment if I didn't change my mind 30 times. :) Second, I'm just trying to figure out what that 'assume-no-escape' property implies. From a C based compiler I would have expected a feature that disallowed address-of on objects, but did not affect any other object referenced from that one (for handling C's 'register' storage class). This is an optimisation not built with a C compiler in mind, nor is it leveraged by C/C++, so I don't think you should think of it in this way. I was actually made aware of this particular attribute when someone spoke to a GNU/Fortran maintainer and thought that INTENT(IN) - or at least the no clobber aspect - could be used to improve optimisations around 'immutable' parameters. Something that gives us the one up that C-family const could never guarantee (currently there is no difference between const and immutable). That is still on the table to do using this attribute pending investigation. The no escape aspect leverages on what 'scope' and 'in' should be enforcing. Third, I'm paranoid when it comes to GDC regressions. Once upon the time I had a working D compiler, one that was able to deliver maybe ~75% of GCC functionality, and where the main issues were with the language and frontend, not with the tool. GCC functionality is not to be confused with C/C++ functionality. And most of the attributes exposed to C-family languages were nothing more an excess baggage, ie: @artificial makes no sense when there is no inline keyword. Anything that needs raising would ideally be in a bug report, as I can't keep track of issues raised in threads. Regards Iain
Re: Missed optimisation case - internal use of STCin
On 21 Apr 2014 09:56, Iain Buclaw ibuc...@gdcproject.org wrote: On 20 Apr 2014 13:19, Artur Skawina via Digitalmars-d digitalmars-d@puremagic.com wrote: On 04/20/14 03:00, Iain Buclaw via Digitalmars-d wrote: On 19 April 2014 17:10, Artur Skawina via Digitalmars-d digitalmars-d@puremagic.com wrote: On 04/19/14 16:21, Iain Buclaw via Digitalmars-d wrote: On 19 April 2014 14:33, Artur Skawina via Digitalmars-d digitalmars-d@puremagic.com wrote: On 04/19/14 14:37, Iain Buclaw via Digitalmars-d wrote: On 19 April 2014 13:02, Artur Skawina via Digitalmars-d digitalmars-d@puremagic.com wrote: On 04/19/14 13:03, Iain Buclaw via Digitalmars-d wrote: On Saturday, 19 April 2014 at 10:49:22 UTC, Iain Buclaw wrote: I'm currently testing out a GCC optimisation that allows you to set call argument flags. The current assumptions being: in parameters = Assume no escape, no clobber (read-only). ref parameters, classes and pointers = Assume worst case. default = Assume no escape. That should read: ref parameters, inout parameters, classes and pointers. The default of assuming no escape is an experiment - I may limit this to only scalar types, and parameters marked as 'scope' (So long as no one plans on deprecating it soon :) What does assume no escape actually mean? [The above list doesn't really make sense. W/o context, it's hard to even tell why, hence the question.] What I was wondering was things like whether that assume no escape property was transitive; if /locally/ escaping was disallowed, and to what extent. What does assume no escape mean at all? In your examples you're mentioning refs together with pointers, that would only make sense if no-escape were transitive -- but then treating all args as no-escape would be very wrong. I'm worried about a) invalid assumptions making it into GDC; b) certain valid assumptions making into GDC. The latter because it could mean that code that's incorrect, but still accepted by the other compilers could silently break when compiled with GDC. Invalid assumptions rarely make it into GDC. The testsuite is a good AFAICT what you're proposing *is* invalid. I can't be sure because it's not clear what that no-escape property means; that's why I asked about it twice already... Clearly, escaping objects reachable indirectly via function arguments is perfectly fine (eg string slicing), yet you wanted to treat args as no-escape by default. Not wanted - experimented. I could not think at the time a use case where a parameter could escape. And *I* have shown a very valid use case to *disprove myself*. I'm not sure of your continual persistence of bringing this up as this is no longer relevant to me. Other than Several reasons. First, I did not realize that you had changed your mind. It wouldn't be an experiment if I didn't change my mind 30 times. :) Second, I'm just trying to figure out what that 'assume-no-escape' property implies. From a C based compiler I would have expected a feature that disallowed address-of on objects, but did not affect any other object referenced from that one (for handling C's 'register' storage class). This is an optimisation not built with a C compiler in mind, nor is it leveraged by C/C++, so I don't think you should think of it in this way. I was actually made aware of this particular attribute when someone spoke to a GNU/Fortran maintainer and thought that INTENT(IN) - or at least the no clobber aspect - could be used to improve optimisations around 'immutable' parameters. Something that gives us the one up that C-family const could never guarantee (currently there is no difference between const and immutable). That is still on the table to do using this attribute pending investigation. The no escape aspect leverages on what 'scope' and 'in' should be enforcing. Third, I'm paranoid when it comes to GDC regressions. Once upon the time I had a working D compiler, one that was able to deliver maybe ~75% of GCC functionality, and where the main issues were with the language and frontend, not with the tool. GCC functionality is not to be confused with C/C++ functionality. And most of the attributes exposed to C-family languages were nothing more an excess baggage, ie: @artificial makes no sense when there is no inline keyword. Anything that needs raising would ideally be in a bug report, as I can't keep track of issues raised in threads. As for the original topic. STCin is an attribute ignored by the compiler (only talking about gdc) - which is a shame because marking parameters as 'in' I see is still encouraged. And I would assume the same is true also for dmd and ldc, otherwise someone would have noticed this bug by now.
Re: Missed optimisation case - internal use of STCin
On 04/20/14 22:11, Iain Buclaw via Digitalmars-d wrote: The failure of inlining is not a blocker IMO It is one in practice. A language with a compiler that can not even inline this trivial function: test %rdi,%rdi sete %al retq is not a viable alternative to C. Not everything can or should be an enum, and D doesn't have macros -- there is no workaround. [That's array.empty. More context, for people not reading the GDC list: http://forum.dlang.org/thread/mailman.75.1396605155.19942.d@puremagic.com ] The bug may be hard to fix, and I really appreciate your effort, but this definitely *is* a major problem. relying on 'hidden' features, NRVO being another example, in user code is a bug. Not if RVO is mandated by a spec. Yes, I had trouble with this in the past too. :) IIRC an auto-return-type related problem was fixed by Walter some time ago; but I still have to maintain the workaround, even after the bug has been fixed upstream... artur
Re: Missed optimisation case - internal use of STCin
On 04/20/14 03:00, Iain Buclaw via Digitalmars-d wrote: On 19 April 2014 17:10, Artur Skawina via Digitalmars-d digitalmars-d@puremagic.com wrote: On 04/19/14 16:21, Iain Buclaw via Digitalmars-d wrote: On 19 April 2014 14:33, Artur Skawina via Digitalmars-d digitalmars-d@puremagic.com wrote: On 04/19/14 14:37, Iain Buclaw via Digitalmars-d wrote: On 19 April 2014 13:02, Artur Skawina via Digitalmars-d digitalmars-d@puremagic.com wrote: On 04/19/14 13:03, Iain Buclaw via Digitalmars-d wrote: On Saturday, 19 April 2014 at 10:49:22 UTC, Iain Buclaw wrote: I'm currently testing out a GCC optimisation that allows you to set call argument flags. The current assumptions being: in parameters = Assume no escape, no clobber (read-only). ref parameters, classes and pointers = Assume worst case. default = Assume no escape. That should read: ref parameters, inout parameters, classes and pointers. The default of assuming no escape is an experiment - I may limit this to only scalar types, and parameters marked as 'scope' (So long as no one plans on deprecating it soon :) What does assume no escape actually mean? [The above list doesn't really make sense. W/o context, it's hard to even tell why, hence the question.] What I was wondering was things like whether that assume no escape property was transitive; if /locally/ escaping was disallowed, and to what extent. What does assume no escape mean at all? In your examples you're mentioning refs together with pointers, that would only make sense if no-escape were transitive -- but then treating all args as no-escape would be very wrong. I'm worried about a) invalid assumptions making it into GDC; b) certain valid assumptions making into GDC. The latter because it could mean that code that's incorrect, but still accepted by the other compilers could silently break when compiled with GDC. Invalid assumptions rarely make it into GDC. The testsuite is a good AFAICT what you're proposing *is* invalid. I can't be sure because it's not clear what that no-escape property means; that's why I asked about it twice already... Clearly, escaping objects reachable indirectly via function arguments is perfectly fine (eg string slicing), yet you wanted to treat args as no-escape by default. Not wanted - experimented. I could not think at the time a use case where a parameter could escape. And *I* have shown a very valid use case to *disprove myself*. I'm not sure of your continual persistence of bringing this up as this is no longer relevant to me. Other than Several reasons. First, I did not realize that you had changed your mind. Second, I'm just trying to figure out what that 'assume-no-escape' property implies. From a C based compiler I would have expected a feature that disallowed address-of on objects, but did not affect any other object referenced from that one (for handling C's 'register' storage class). Third, I'm paranoid when it comes to GDC regressions. Once upon the time I had a working D compiler, one that was able to deliver maybe ~75% of GCC functionality, and where the main issues were with the language and frontend, not with the tool. This was a few years ago, after you'd fixed the many small problems I had run into. The type of those issues made it very clear that I was the only one that was trying to really use GDC. Unfortunately what happened then was that things started to get worse, and by worse I mean unusable; GDC ceased to be able to deliver functionality and performance that was in the same league as GCC C/C++. LTO stopped working (which is not only crucial for a language w/o macros and low-level control, but was useful as a work-around for tool issues, like the lack of cross module inlining). The accepted language changed in a way that was completely backward incompatible and would have required an extra preprocessing step (pragma-attributes were removed and became hard errors). GCC attributes became inaccessible; things like @pure, @malloc, @ifunc, @align, @cold, @regparm all used to work, but now didn't. @inline, @noinline and @flatten were added back as /true/ D-style attributes later, and seem to work great. Thanks for exposing those, but my concern is that dealing with them one-by-one does not scale - that's why I haven't filed any bug reports wrt the other ones. Your work on getting D support merged into GCC is critically important for the survival of the language; things that are merely optimizations can happen later, or will be mostly irrelevant (if the merge never happens). But the situation right now is that the latest GDC version that works is the gcc4.6 one (IIRC 2.057 based) - I have tried to migrate to a newer one maybe 5 or 6 times over the last 1.5 year, and always run into some kind of problem immediately after trying a new build. Like the last time, with the failure of inlining of certain trivial functions. So when I then read about a proposed new optimization, which sounds
Re: Missed optimisation case - internal use of STCin
On 20 April 2014 13:19, Artur Skawina via Digitalmars-d digitalmars-d@puremagic.com wrote: On 04/20/14 03:00, Iain Buclaw via Digitalmars-d wrote: On 19 April 2014 17:10, Artur Skawina via Digitalmars-d digitalmars-d@puremagic.com wrote: On 04/19/14 16:21, Iain Buclaw via Digitalmars-d wrote: On 19 April 2014 14:33, Artur Skawina via Digitalmars-d digitalmars-d@puremagic.com wrote: On 04/19/14 14:37, Iain Buclaw via Digitalmars-d wrote: On 19 April 2014 13:02, Artur Skawina via Digitalmars-d digitalmars-d@puremagic.com wrote: On 04/19/14 13:03, Iain Buclaw via Digitalmars-d wrote: On Saturday, 19 April 2014 at 10:49:22 UTC, Iain Buclaw wrote: I'm currently testing out a GCC optimisation that allows you to set call argument flags. The current assumptions being: in parameters = Assume no escape, no clobber (read-only). ref parameters, classes and pointers = Assume worst case. default = Assume no escape. That should read: ref parameters, inout parameters, classes and pointers. The default of assuming no escape is an experiment - I may limit this to only scalar types, and parameters marked as 'scope' (So long as no one plans on deprecating it soon :) What does assume no escape actually mean? [The above list doesn't really make sense. W/o context, it's hard to even tell why, hence the question.] What I was wondering was things like whether that assume no escape property was transitive; if /locally/ escaping was disallowed, and to what extent. What does assume no escape mean at all? In your examples you're mentioning refs together with pointers, that would only make sense if no-escape were transitive -- but then treating all args as no-escape would be very wrong. I'm worried about a) invalid assumptions making it into GDC; b) certain valid assumptions making into GDC. The latter because it could mean that code that's incorrect, but still accepted by the other compilers could silently break when compiled with GDC. Invalid assumptions rarely make it into GDC. The testsuite is a good AFAICT what you're proposing *is* invalid. I can't be sure because it's not clear what that no-escape property means; that's why I asked about it twice already... Clearly, escaping objects reachable indirectly via function arguments is perfectly fine (eg string slicing), yet you wanted to treat args as no-escape by default. Not wanted - experimented. I could not think at the time a use case where a parameter could escape. And *I* have shown a very valid use case to *disprove myself*. I'm not sure of your continual persistence of bringing this up as this is no longer relevant to me. Other than Several reasons. First, I did not realize that you had changed your mind. Second, I'm just trying to figure out what that 'assume-no-escape' property implies. From a C based compiler I would have expected a feature that disallowed address-of on objects, but did not affect any other object referenced from that one (for handling C's 'register' storage class). Third, I'm paranoid when it comes to GDC regressions. Once upon the time I had a working D compiler, one that was able to deliver maybe ~75% of GCC functionality, and where the main issues were with the language and frontend, not with the tool. This was a few years ago, after you'd fixed the many small problems I had run into. The type of those issues made it very clear that I was the only one that was trying to really use GDC. Unfortunately what happened then was that things started to get worse, and by worse I mean unusable; GDC ceased to be able to deliver functionality and performance that was in the same league as GCC C/C++. LTO stopped working (which is not only crucial for a language w/o macros and low-level control, but was useful as a work-around for tool issues, like the lack of cross module inlining). I have not seen this, infact the opposite. As for speed of runtime. Many of the optimisations that were removed in the last year have been found when porting to architectures that are less forgiving than x86. I still don't what's up with LTO. It's not easy to debug, and fails in a way that doesn't seem to suggest a front-end problem (it chokes when reading LTO information written by itself). The accepted language changed in a way that was completely backward incompatible and would have required an extra preprocessing step (pragma-attributes were removed and became hard errors). GCC attributes became inaccessible; things like @pure, @malloc, @ifunc, @align, @cold, @regparm all used to work, but now didn't. @inline, @noinline and @flatten were added back as /true/ D-style attributes later, and seem to work great. Many of these attributes to which need a good reason to be hashed out. Originally my intention was to only expose those that are impossible to infer otherwise in D through existing language features. Thanks for exposing those, but my concern is that dealing with them one-by-one does not scale
Missed optimisation case - internal use of STCin
Hi, I'm currently testing out a GCC optimisation that allows you to set call argument flags. The current assumptions being: in parameters = Assume no escape, no clobber (read-only). ref parameters, classes and pointers = Assume worst case. default = Assume no escape. See here for implementation details: http://gcc.gnu.org/ml/fortran/2010-05/msg00032.html The idea for the 'in' parameters being that if we have the following: -- bool somefunc (in char[] a); The compiler can assume that whatever parameters are passed, they do not changes. So the compiler can more aggressively optimise the following case, for instance. eg: -- char[] foo = bar; assert(foo == bar); somefunc(foo); assert(foo == bar); One problem I've found with this though, is that the front-end tends to set all library function parameters as STCin, so the optimisation is fundamentally broken: eg: -- int[3] arr = [2,3,1]; arr.sort; // Defined internally as _adSort(in void[], in TypeInfo); assert(arr[0] == 1); // Compiler infers as false, throws assert. I think it would be more than reasonable to fix the frontend here so that the internal representation better matches that found in the internal runtime library. Just wanted to pass this by you guys first. Regards Iain.
Re: Missed optimisation case - internal use of STCin
On Saturday, 19 April 2014 at 10:49:22 UTC, Iain Buclaw wrote: Hi, I'm currently testing out a GCC optimisation that allows you to set call argument flags. The current assumptions being: in parameters = Assume no escape, no clobber (read-only). ref parameters, classes and pointers = Assume worst case. default = Assume no escape. That should read: ref parameters, inout parameters, classes and pointers. The default of assuming no escape is an experiment - I may limit this to only scalar types, and parameters marked as 'scope' (So long as no one plans on deprecating it soon :)
Re: Missed optimisation case - internal use of STCin
On 04/19/14 13:03, Iain Buclaw via Digitalmars-d wrote: On Saturday, 19 April 2014 at 10:49:22 UTC, Iain Buclaw wrote: Hi, I'm currently testing out a GCC optimisation that allows you to set call argument flags. The current assumptions being: in parameters = Assume no escape, no clobber (read-only). ref parameters, classes and pointers = Assume worst case. default = Assume no escape. That should read: ref parameters, inout parameters, classes and pointers. The default of assuming no escape is an experiment - I may limit this to only scalar types, and parameters marked as 'scope' (So long as no one plans on deprecating it soon :) What does assume no escape actually mean? [The above list doesn't really make sense. W/o context, it's hard to even tell why, hence the question.] Also, 'inout' is about constness -- doesn't affect lifetime and reachability, but does imply no clobbering. artur
Re: Missed optimisation case - internal use of STCin
On 19 April 2014 13:02, Artur Skawina via Digitalmars-d digitalmars-d@puremagic.com wrote: On 04/19/14 13:03, Iain Buclaw via Digitalmars-d wrote: On Saturday, 19 April 2014 at 10:49:22 UTC, Iain Buclaw wrote: Hi, I'm currently testing out a GCC optimisation that allows you to set call argument flags. The current assumptions being: in parameters = Assume no escape, no clobber (read-only). ref parameters, classes and pointers = Assume worst case. default = Assume no escape. That should read: ref parameters, inout parameters, classes and pointers. The default of assuming no escape is an experiment - I may limit this to only scalar types, and parameters marked as 'scope' (So long as no one plans on deprecating it soon :) What does assume no escape actually mean? [The above list doesn't really make sense. W/o context, it's hard to even tell why, hence the question.] Also, 'inout' is about constness -- doesn't affect lifetime and reachability, but does imply no clobbering. 'out' parameters - I sometimes confuse the two when I have a head cold. :o)
Re: Missed optimisation case - internal use of STCin
On 19 April 2014 13:02, Artur Skawina via Digitalmars-d
digitalmars-d@puremagic.com wrote:
On 04/19/14 13:03, Iain Buclaw via Digitalmars-d wrote:
On Saturday, 19 April 2014 at 10:49:22 UTC, Iain Buclaw wrote:
Hi,
I'm currently testing out a GCC optimisation that allows you to set call
argument flags. The current assumptions being:
in parameters = Assume no escape, no clobber (read-only).
ref parameters, classes and pointers = Assume worst case.
default = Assume no escape.
That should read:
ref parameters, inout parameters, classes and pointers.
The default of assuming no escape is an experiment - I may limit this to
only scalar types, and parameters marked as 'scope' (So long as no one
plans on deprecating it soon :)
What does assume no escape actually mean?
[The above list doesn't really make sense. W/o context, it's
hard to even tell why, hence the question.]
Actually, I might change the default to assume worst case. I've just
tried this out, which is still valid.
class C {
int * p;
this(int x) {
p = x; // escapes the address of the parameter.
}
}
Worse, scope doesn't error on the general case either.
class D {
int * p;
this(scope int x) {
p = x; // escapes the address of the scope parameter.
}
}
Do these examples give you a good example?
Re: Missed optimisation case - internal use of STCin
On 04/19/14 14:37, Iain Buclaw via Digitalmars-d wrote:
On 19 April 2014 13:02, Artur Skawina via Digitalmars-d
digitalmars-d@puremagic.com wrote:
On 04/19/14 13:03, Iain Buclaw via Digitalmars-d wrote:
On Saturday, 19 April 2014 at 10:49:22 UTC, Iain Buclaw wrote:
Hi,
I'm currently testing out a GCC optimisation that allows you to set call
argument flags. The current assumptions being:
in parameters = Assume no escape, no clobber (read-only).
ref parameters, classes and pointers = Assume worst case.
default = Assume no escape.
That should read:
ref parameters, inout parameters, classes and pointers.
The default of assuming no escape is an experiment - I may limit this to
only scalar types, and parameters marked as 'scope' (So long as no one
plans on deprecating it soon :)
What does assume no escape actually mean?
[The above list doesn't really make sense. W/o context, it's
hard to even tell why, hence the question.]
Actually, I might change the default to assume worst case. I've just
tried this out, which is still valid.
class C {
int * p;
this(int x) {
p = x; // escapes the address of the parameter.
}
}
This might be currently accepted, but it is clearly invalid
(escapes local; the only way to make it work safely would
be to silently copy 'x' to the GC-managed heap, which would be
way too costly).
A f(A a) { g(a); return a; } // likewise with ref instead of pointer.
This is OK (even if ideally 'g' should be forbidden from escaping 'a').
Similarly:
A f(A a) {
auto o = register(a); // can modify 'a'
o.blah(); // ditto
doneWith(o); // ditto
return a;
}
What I was wondering was things like whether that assume no escape
property was transitive; if /locally/ escaping was disallowed, and
to what extent. What does assume no escape mean at all? In your
examples you're mentioning refs together with pointers, that would
only make sense if no-escape were transitive -- but then treating all
args as no-escape would be very wrong.
Worse, scope doesn't error on the general case either.
class D {
int * p;
this(scope int x) {
p = x; // escapes the address of the scope parameter.
}
}
D's scope isn't enforced in any way right now, which means
that code could exist that is invalid, but currently works. It
would break silently(!) when compiled with a decent compiler,
which still doesn't enforce scope.
Do these examples give you a good example?
I'm worried about a) invalid assumptions making it into GDC;
b) certain valid assumptions making into GDC. The latter because
it could mean that code that's incorrect, but still accepted by
the other compilers could silently break when compiled with GDC.
artur
Re: Missed optimisation case - internal use of STCin
On 19 April 2014 14:33, Artur Skawina via Digitalmars-d
digitalmars-d@puremagic.com wrote:
On 04/19/14 14:37, Iain Buclaw via Digitalmars-d wrote:
On 19 April 2014 13:02, Artur Skawina via Digitalmars-d
digitalmars-d@puremagic.com wrote:
On 04/19/14 13:03, Iain Buclaw via Digitalmars-d wrote:
On Saturday, 19 April 2014 at 10:49:22 UTC, Iain Buclaw wrote:
Hi,
I'm currently testing out a GCC optimisation that allows you to set call
argument flags. The current assumptions being:
in parameters = Assume no escape, no clobber (read-only).
ref parameters, classes and pointers = Assume worst case.
default = Assume no escape.
That should read:
ref parameters, inout parameters, classes and pointers.
The default of assuming no escape is an experiment - I may limit this to
only scalar types, and parameters marked as 'scope' (So long as no one
plans on deprecating it soon :)
What does assume no escape actually mean?
[The above list doesn't really make sense. W/o context, it's
hard to even tell why, hence the question.]
Actually, I might change the default to assume worst case. I've just
tried this out, which is still valid.
class C {
int * p;
this(int x) {
p = x; // escapes the address of the parameter.
}
}
This might be currently accepted, but it is clearly invalid
(escapes local; the only way to make it work safely would
be to silently copy 'x' to the GC-managed heap, which would be
way too costly).
A f(A a) { g(a); return a; } // likewise with ref instead of pointer.
This is OK (even if ideally 'g' should be forbidden from escaping 'a').
Similarly:
A f(A a) {
auto o = register(a); // can modify 'a'
o.blah(); // ditto
doneWith(o); // ditto
return a;
}
What I was wondering was things like whether that assume no escape
property was transitive; if /locally/ escaping was disallowed, and
to what extent. What does assume no escape mean at all? In your
examples you're mentioning refs together with pointers, that would
only make sense if no-escape were transitive -- but then treating all
args as no-escape would be very wrong.
Worse, scope doesn't error on the general case either.
class D {
int * p;
this(scope int x) {
p = x; // escapes the address of the scope parameter.
}
}
D's scope isn't enforced in any way right now, which means
that code could exist that is invalid, but currently works. It
would break silently(!) when compiled with a decent compiler,
which still doesn't enforce scope.
People should get bug fixing soon then. =)
Do these examples give you a good example?
I'm worried about a) invalid assumptions making it into GDC;
b) certain valid assumptions making into GDC. The latter because
it could mean that code that's incorrect, but still accepted by
the other compilers could silently break when compiled with GDC.
Invalid assumptions rarely make it into GDC. The testsuite is a good
bench for this, as well as several projects (now I've got dub set-up)
to test it in the wild.
Saying that, we have had to revert some optimisation cases as D's
schizophrenic nature of enforcing attributes and behaviours is
becoming increasingly dismal.
eg:
- nothrow has *no* guarantee, period, because it still allows
unrecoverable errors being thrown, and allows people to catch said
unrecoverable errors.
- pure is a tough nut to crack also. The theory should allow you to
be able to cache return values, but in practise...
- The nature of debug statements breaks guarantees of both nothrow and
pure, possibly many more.
- Defining reliable strict aliasing rules, it turns out, is not that
simple (this is something that Walter has mentioned about D should
have good guarantees for, ie: D arrays).
I'm just in investigating all avenues, as I usually do. There is no
reason why 'in' shouldn't have more powerful guarantees IMO, and what
I've found is not a problem with user code, it's a problem with the
compiler implementation.
For reference, this is the declaration of _adSort in rt.qsort:
extern (C) void[] _adSort(void[], TypeInfo);
This is how the compiler frontend defines the function internally for
its own use:
extern (C) T[] _adSort(in void[], in TypeInfo);
Re: Missed optimisation case - internal use of STCin
On Saturday, 19 April 2014 at 14:21:23 UTC, Iain Buclaw via Digitalmars-d wrote: eg: - nothrow has *no* guarantee, period, because it still allows unrecoverable errors being thrown, and allows people to catch said unrecoverable errors. Hm, it is hard to find clear answer in spec but I _think_ that replacing error throwing with program halting in release mode for nothrow function should be valid behavior.
Re: Missed optimisation case - internal use of STCin
On 19 April 2014 15:36, Dicebot via Digitalmars-d digitalmars-d@puremagic.com wrote: On Saturday, 19 April 2014 at 14:21:23 UTC, Iain Buclaw via Digitalmars-d wrote: eg: - nothrow has *no* guarantee, period, because it still allows unrecoverable errors being thrown, and allows people to catch said unrecoverable errors. Hm, it is hard to find clear answer in spec but I _think_ that replacing error throwing with program halting in release mode for nothrow function should be valid behavior. Nope. I can't recall the exact code, but an example is in the testsuite. It was discovered when porting to ARM, which was found to omit unwind directives for D nothrow functions, causing runtime hangs when said 'nothrow' functions infact threw an Error.
Re: Missed optimisation case - internal use of STCin
On Saturday, 19 April 2014 at 15:00:26 UTC, Iain Buclaw via Digitalmars-d wrote: Nope. I can't recall the exact code, but an example is in the testsuite. It was discovered when porting to ARM, which was found to omit unwind directives for D nothrow functions, causing runtime hangs when said 'nothrow' functions infact threw an Error. Now I am pretty sure _this_ is a druntime bug. I don't know about being able to catch actual exception but the fact that unwinding is not guaranteed for Errors is mentioned either on dlang.org or in TDPL.
Re: Missed optimisation case - internal use of STCin
On 04/19/14 16:21, Iain Buclaw via Digitalmars-d wrote:
On 19 April 2014 14:33, Artur Skawina via Digitalmars-d
digitalmars-d@puremagic.com wrote:
On 04/19/14 14:37, Iain Buclaw via Digitalmars-d wrote:
On 19 April 2014 13:02, Artur Skawina via Digitalmars-d
digitalmars-d@puremagic.com wrote:
On 04/19/14 13:03, Iain Buclaw via Digitalmars-d wrote:
On Saturday, 19 April 2014 at 10:49:22 UTC, Iain Buclaw wrote:
I'm currently testing out a GCC optimisation that allows you to set call
argument flags. The current assumptions being:
in parameters = Assume no escape, no clobber (read-only).
ref parameters, classes and pointers = Assume worst case.
default = Assume no escape.
That should read:
ref parameters, inout parameters, classes and pointers.
The default of assuming no escape is an experiment - I may limit this to
only scalar types, and parameters marked as 'scope' (So long as no one
plans on deprecating it soon :)
What does assume no escape actually mean?
[The above list doesn't really make sense. W/o context, it's
hard to even tell why, hence the question.]
Actually, I might change the default to assume worst case. I've just
tried this out, which is still valid.
class C {
int * p;
this(int x) {
p = x; // escapes the address of the parameter.
}
}
This might be currently accepted, but it is clearly invalid
(escapes local; the only way to make it work safely would
be to silently copy 'x' to the GC-managed heap, which would be
way too costly).
A f(A a) { g(a); return a; } // likewise with ref instead of pointer.
This is OK (even if ideally 'g' should be forbidden from escaping 'a').
Similarly:
A f(A a) {
auto o = register(a); // can modify 'a'
o.blah(); // ditto
doneWith(o); // ditto
return a;
}
What I was wondering was things like whether that assume no escape
property was transitive; if /locally/ escaping was disallowed, and
to what extent. What does assume no escape mean at all? In your
examples you're mentioning refs together with pointers, that would
only make sense if no-escape were transitive -- but then treating all
args as no-escape would be very wrong.
Worse, scope doesn't error on the general case either.
class D {
int * p;
this(scope int x) {
p = x; // escapes the address of the scope parameter.
}
}
D's scope isn't enforced in any way right now, which means
that code could exist that is invalid, but currently works. It
would break silently(!) when compiled with a decent compiler,
which still doesn't enforce scope.
People should get bug fixing soon then. =)
Until some kind of diagnostics appear, most of those bugs won't
even be found. It's too easy to write auto f (in A a) and then
forget about the implicit 'scope' when modifying the function body.
Do these examples give you a good example?
I'm worried about a) invalid assumptions making it into GDC;
b) certain valid assumptions making into GDC. The latter because
it could mean that code that's incorrect, but still accepted by
the other compilers could silently break when compiled with GDC.
Invalid assumptions rarely make it into GDC. The testsuite is a good
AFAICT what you're proposing *is* invalid. I can't be sure because
it's not clear what that no-escape property means; that's why I
asked about it twice already...
Clearly, escaping objects reachable indirectly via function arguments
is perfectly fine (eg string slicing), yet you wanted to treat args as
no-escape by default.
Also, treating /some/ types specially wouldn't be ideal;
struct A { int a; /* no pointers or classes */ }
struct B { int* b; /*...*/ }
f(A); // should be treated similarly to 'f(int)'
f(B); // should be treated similarly to 'f(int*)'
Yes, not doing it is just a missed optimization, but in practice
it means that wrapping types becomes even more expensive in D (it's
already almost prohibitively so - eg returning small one-element
structs from functions needlessly happens by ref).
bench for this, as well as several projects (now I've got dub set-up)
to test it in the wild.
These problems will result in invalid optimizations, so can be hard
to trigger and may come and go away randomly.
Saying that, we have had to revert some optimisation cases as D's
schizophrenic nature of enforcing attributes and behaviours is
becoming increasingly dismal.
eg:
- nothrow has *no* guarantee, period, because it still allows
unrecoverable errors being thrown, and allows people to catch said
unrecoverable errors.
- pure is a tough nut to crack also. The theory should allow you to
be able to cache return values, but in practise...
D's pure doesn't have much in common with the normal pure concept;
exposing gcc's pure via an attribute and completely ignoring D's
version is probably the only practical solution, anything else would
be too costly, result in too small gains, and
Re: Missed optimisation case - internal use of STCin
On 19 April 2014 17:10, Artur Skawina via Digitalmars-d
digitalmars-d@puremagic.com wrote:
On 04/19/14 16:21, Iain Buclaw via Digitalmars-d wrote:
On 19 April 2014 14:33, Artur Skawina via Digitalmars-d
digitalmars-d@puremagic.com wrote:
On 04/19/14 14:37, Iain Buclaw via Digitalmars-d wrote:
On 19 April 2014 13:02, Artur Skawina via Digitalmars-d
digitalmars-d@puremagic.com wrote:
On 04/19/14 13:03, Iain Buclaw via Digitalmars-d wrote:
On Saturday, 19 April 2014 at 10:49:22 UTC, Iain Buclaw wrote:
I'm currently testing out a GCC optimisation that allows you to set
call argument flags. The current assumptions being:
in parameters = Assume no escape, no clobber (read-only).
ref parameters, classes and pointers = Assume worst case.
default = Assume no escape.
That should read:
ref parameters, inout parameters, classes and pointers.
The default of assuming no escape is an experiment - I may limit this to
only scalar types, and parameters marked as 'scope' (So long as no one
plans on deprecating it soon :)
What does assume no escape actually mean?
[The above list doesn't really make sense. W/o context, it's
hard to even tell why, hence the question.]
Actually, I might change the default to assume worst case. I've just
tried this out, which is still valid.
class C {
int * p;
this(int x) {
p = x; // escapes the address of the parameter.
}
}
This might be currently accepted, but it is clearly invalid
(escapes local; the only way to make it work safely would
be to silently copy 'x' to the GC-managed heap, which would be
way too costly).
A f(A a) { g(a); return a; } // likewise with ref instead of pointer.
This is OK (even if ideally 'g' should be forbidden from escaping 'a').
Similarly:
A f(A a) {
auto o = register(a); // can modify 'a'
o.blah(); // ditto
doneWith(o); // ditto
return a;
}
What I was wondering was things like whether that assume no escape
property was transitive; if /locally/ escaping was disallowed, and
to what extent. What does assume no escape mean at all? In your
examples you're mentioning refs together with pointers, that would
only make sense if no-escape were transitive -- but then treating all
args as no-escape would be very wrong.
Worse, scope doesn't error on the general case either.
class D {
int * p;
this(scope int x) {
p = x; // escapes the address of the scope parameter.
}
}
D's scope isn't enforced in any way right now, which means
that code could exist that is invalid, but currently works. It
would break silently(!) when compiled with a decent compiler,
which still doesn't enforce scope.
People should get bug fixing soon then. =)
Until some kind of diagnostics appear, most of those bugs won't
even be found. It's too easy to write auto f (in A a) and then
forget about the implicit 'scope' when modifying the function body.
Do these examples give you a good example?
I'm worried about a) invalid assumptions making it into GDC;
b) certain valid assumptions making into GDC. The latter because
it could mean that code that's incorrect, but still accepted by
the other compilers could silently break when compiled with GDC.
Invalid assumptions rarely make it into GDC. The testsuite is a good
AFAICT what you're proposing *is* invalid. I can't be sure because
it's not clear what that no-escape property means; that's why I
asked about it twice already...
Clearly, escaping objects reachable indirectly via function arguments
is perfectly fine (eg string slicing), yet you wanted to treat args as
no-escape by default.
Not wanted - experimented. I could not think at the time a use case
where a parameter could escape. And *I* have shown a very valid use
case to *disprove myself*. I'm not sure of your continual persistence
of bringing this up as this is no longer relevant to me. Other than
possibly the silent breaking of 'scope' or 'in' parameters that are
misused (accepts invalid bugs).
bench for this, as well as several projects (now I've got dub set-up)
to test it in the wild.
These problems will result in invalid optimizations, so can be hard
to trigger and may come and go away randomly.
Saying that, we have had to revert some optimisation cases as D's
schizophrenic nature of enforcing attributes and behaviours is
becoming increasingly dismal.
eg:
- nothrow has *no* guarantee, period, because it still allows
unrecoverable errors being thrown, and allows people to catch said
unrecoverable errors.
- pure is a tough nut to crack also. The theory should allow you to
be able to cache return values, but in practise...
D's pure doesn't have much in common with the normal pure concept;
exposing gcc's pure via an attribute and completely ignoring D's
version is probably the only practical solution, anything else would
be too costly, result in too small gains, and be too hard to
