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* [Bug middle-end/101063] New: #pragma STDC FENV_ACCESS ON: wrong code generation: instructions leading to side effects may not be generated
@ 2021-06-14 11:10 pavel.morozkin at gmail dot com
2021-06-14 12:46 ` [Bug middle-end/101063] " glisse at gcc dot gnu.org
2021-06-14 19:06 ` pinskia at gcc dot gnu.org
0 siblings, 2 replies; 3+ messages in thread
From: pavel.morozkin at gmail dot com @ 2021-06-14 11:10 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101063
Bug ID: 101063
Summary: #pragma STDC FENV_ACCESS ON: wrong code generation:
instructions leading to side effects may not be
generated
Product: gcc
Version: 11.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: middle-end
Assignee: unassigned at gcc dot gnu.org
Reporter: pavel.morozkin at gmail dot com
Target Milestone: ---
Bug-triggering code (t0.c):
#include <stdio.h>
#include <fenv.h>
#include <float.h>
#pragma STDC FENV_ACCESS ON
int main( void )
{
volatile double d1 = DBL_MAX;
volatile double d2 = DBL_MAX;
#ifdef __STDC__
printf("__STDC__ %d\n", __STDC__);
#endif
#ifdef __STDC_VERSION__
printf("__STDC_VERSION__ %ld\n", __STDC_VERSION__);
#endif
#ifdef __STDC_IEC_559__
printf("__STDC_IEC_559__ %d\n", __STDC_IEC_559__);
#endif
feclearexcept( FE_ALL_EXCEPT );
( void )( d1 * d2 );
if ( fetestexcept( FE_OVERFLOW ) )
{
return 0;
}
printf("error: no FE_OVERFLOW is raised\n");
return 1;
}
Invocation: gcc t0.c -lm && ./a.out
Expected output:
__STDC__ 1
__STDC_VERSION__ 201710
__STDC_IEC_559__ 1
Actual output:
__STDC__ 1
__STDC_VERSION__ 201710
__STDC_IEC_559__ 1
error: no FE_OVERFLOW is raised
Note 1: Under -Wall gcc generates warning:
<source>:5: warning: ignoring '#pragma STDC FENV_ACCESS' [-Wunknown-pragmas]
5 | #pragma STDC FENV_ACCESS ON
Note 2: Comparison with clang: https://godbolt.org/z/6GnqTYvaa.
Brief difference:
gcc:
call feclearexcept
movsd xmm0, QWORD PTR [rbp-8]
movsd xmm0, QWORD PTR [rbp-16]
mov edi, 8
call fetestexcept
clang:
call feclearexcept
movsd xmm0, qword ptr [rbp - 16] # xmm0 = mem[0],zero
movsd xmm1, qword ptr [rbp - 24] # xmm1 = mem[0],zero
mulsd xmm0, xmm1
mov edi, 8
call fetestexcept
Here we see that gcc does not generate "mulsd", which is a bug, because
execution of "mulsd" leads to side effects.
^ permalink raw reply [flat|nested] 3+ messages in thread
* [Bug middle-end/101063] #pragma STDC FENV_ACCESS ON: wrong code generation: instructions leading to side effects may not be generated
2021-06-14 11:10 [Bug middle-end/101063] New: #pragma STDC FENV_ACCESS ON: wrong code generation: instructions leading to side effects may not be generated pavel.morozkin at gmail dot com
@ 2021-06-14 12:46 ` glisse at gcc dot gnu.org
2021-06-14 19:06 ` pinskia at gcc dot gnu.org
1 sibling, 0 replies; 3+ messages in thread
From: glisse at gcc dot gnu.org @ 2021-06-14 12:46 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101063
--- Comment #1 from Marc Glisse <glisse at gcc dot gnu.org> ---
> Note 1: Under -Wall gcc generates warning:
> <source>:5: warning: ignoring '#pragma STDC FENV_ACCESS' [-Wunknown-pragmas]
That seems like a huge hint, this is not implemented in gcc. You can find
several existing PR in this bugzilla.
There is a branch refs/users/glisse/heads/fenv that was kind of functional last
time I tried, but I'll never have time to polish it.
^ permalink raw reply [flat|nested] 3+ messages in thread
* [Bug middle-end/101063] #pragma STDC FENV_ACCESS ON: wrong code generation: instructions leading to side effects may not be generated
2021-06-14 11:10 [Bug middle-end/101063] New: #pragma STDC FENV_ACCESS ON: wrong code generation: instructions leading to side effects may not be generated pavel.morozkin at gmail dot com
2021-06-14 12:46 ` [Bug middle-end/101063] " glisse at gcc dot gnu.org
@ 2021-06-14 19:06 ` pinskia at gcc dot gnu.org
1 sibling, 0 replies; 3+ messages in thread
From: pinskia at gcc dot gnu.org @ 2021-06-14 19:06 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101063
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |RESOLVED
Resolution|--- |DUPLICATE
--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Dup of bug 29186 (and others).
*** This bug has been marked as a duplicate of bug 29186 ***
^ permalink raw reply [flat|nested] 3+ messages in thread
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2021-06-14 11:10 [Bug middle-end/101063] New: #pragma STDC FENV_ACCESS ON: wrong code generation: instructions leading to side effects may not be generated pavel.morozkin at gmail dot com
2021-06-14 12:46 ` [Bug middle-end/101063] " glisse at gcc dot gnu.org
2021-06-14 19:06 ` pinskia at gcc dot gnu.org
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