Re: [PATCH] tree-optimization/106912 - IPA profile and pure/const

[Richard Biener <rguenther@suse.de>]

> Am 25.11.2022 um 11:05 schrieb Jan Hubicka via Gcc-patches <gcc-patches@gcc.gnu.org>:
> 
> 
>> 
>> IPA profile instrumentation tries to clear the pure and const
>> flags of functions but that's quite hopeless in particular for
>> const since that attribute prevails on the type and thus on each
>> call to the function leading to inconsistencies in the IL and
>> eventual checking ICEs.  There's no good reason to do this and
>> it wouldn't fixup any indirect calls so just don't.  No other
>> instrumentation GCC does bothers about this.
> 
> This was mostly meant to deadl with situation where we auto-detect
> function to be const and then partially inline it to a loop.
> Then both caller and callee accesses same counters in the memory and if
> you move load/stores out of the loop in caller you lose counters and get
> inconsistencies at profile read-in time.

Don’t we Instrument after partial inlining now?  As said, since we have the fntype on the call this doesn’t work anymore for const functions via attributes.

Richard 
> Honza
>> 
>> Bootstrap and regtest pending on x86_64-unknown-linux-gnu, OK?
>> 
>> Thanks,
>> Richard.
>> 
>>    PR tree-optimization/106912
>>    * tree-profile.cc (tree_profiling): Do not clear pure/const
>>    flags.
>> 
>>    * gcc.dg/pr106912.c: New testcase.
>> ---
>> gcc/testsuite/gcc.dg/pr106912.c | 16 ++++++++++++++++
>> gcc/tree-profile.cc             |  3 ---
>> 2 files changed, 16 insertions(+), 3 deletions(-)
>> create mode 100644 gcc/testsuite/gcc.dg/pr106912.c
>> 
>> diff --git a/gcc/testsuite/gcc.dg/pr106912.c b/gcc/testsuite/gcc.dg/pr106912.c
>> new file mode 100644
>> index 00000000000..8faa877d8b3
>> --- /dev/null
>> +++ b/gcc/testsuite/gcc.dg/pr106912.c
>> @@ -0,0 +1,16 @@
>> +/* { dg-do compile } */
>> +/* { dg-options "-O2 -fPIC -ftree-vectorize -fprofile-generate" } */
>> +
>> +__attribute__ ((__simd__))
>> +__attribute__ ((__nothrow__ , __leaf__ , __const__))
>> +double foo (double x);
>> +void bar(double *f, int n)
>> +{
>> +  int i;
>> +  for (i = 0; i < n; i++)
>> +    f[i] = foo(f[i]);
>> +}
>> +double foo(double x)
>> +{
>> +  return x * x / 3.0;
>> +}
>> diff --git a/gcc/tree-profile.cc b/gcc/tree-profile.cc
>> index 2beb49241f2..5491b398870 100644
>> --- a/gcc/tree-profile.cc
>> +++ b/gcc/tree-profile.cc
>> @@ -814,9 +814,6 @@ tree_profiling (void)
>>    /* Don't profile functions produced for builtin stuff.  */
>>    if (DECL_SOURCE_LOCATION (node->decl) == BUILTINS_LOCATION)
>>      continue;
>> -
>> -    node->set_const_flag (false, false);
>> -    node->set_pure_flag (false, false);
>>       }
>> 
>>   /* Update call statements and rebuild the cgraph.  */
>> -- 
>> 2.35.3