https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108318
Bug ID: 108318
Summary: Floating point calculation moved out of loop despite
fesetround
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: rtl-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: tkoenig at gcc dot gnu.org
Target Milestone: ---
#include <fenv.h>
void
foo (double res[4], double a, double b)
{
static const int rm[4]
= { FE_DOWNWARD, FE_TONEAREST, FE_TOWARDZERO, FE_UPWARD };
for (int i = 0; i < 4; ++i)
{
fesetround (rm[i]);
res[i] = a + b;
}
fesetround (FE_TONEAREST); // restore default
}
when compiled with recent trunk and -O3, yields
addsd %xmm1, %xmm0
pushq %r14
.cfi_def_cfa_offset 16
.cfi_offset 14, -16
pushq %rbp
.cfi_def_cfa_offset 24
.cfi_offset 6, -24
movq %rdi, %rbp
pushq %rbx
.cfi_def_cfa_offset 32
.cfi_offset 3, -32
xorl %ebx, %ebx
movq %xmm0, %r14
.L2:
movl rm.0(,%rbx,4), %edi
call fesetround
movq %r14, 0(%rbp,%rbx,8)
addq $1, %rbx
cmpq $4, %rbx
jne .L2
popq %rbx
.cfi_def_cfa_offset 24
xorl %edi, %edi
popq %rbp
.cfi_def_cfa_offset 16
popq %r14
.cfi_def_cfa_offset 8
jmp fesetround
.cfi_endproc
Seems all right after tree optimization, the *.optimized dump looks OK:
<bb 3> [local count: 858993457]:
# ivtmp.5_16 = PHI <ivtmp.5_7(3), 0(2)>
_1 = MEM[(int *)&rm + ivtmp.5_16 * 4];
fesetround (_1);
_5 = a_12(D) + b_13(D);
MEM[(double *)res_11(D) + ivtmp.5_16 * 8] = _5;
ivtmp.5_7 = ivtmp.5_16 + 1;
if (ivtmp.5_7 != 4)
goto <bb 3>; [80.00%]
else
goto <bb 4>; [20.00%]
<bb 4> [local count: 214748368]:
fesetround (0); [tail call]
return;
This does not seem to be a recent regression, this goes back to at
least gcc 4.1.2.
Noted by Michael S on comp.arch, on
https://groups.google.com/g/comp.arch/c/Izheu-k00Nw/m/oljg70SBBwAJ .
