https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85633
Bug ID: 85633
Summary: [8 Regression] reorders function ignoring fpu
exception state
Product: gcc
Version: 8.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: jtaylor.debian at googlemail dot com
Target Milestone: ---
gcc-8 seems to ignore the global fpu exception state when reordering functions.
In this example it reorders the fpu_invalid_set_function which is _not_ marked
as const before the last _mm_min_ps call which can set the fpu invalid
exception.
#include <emmintrin.h>
int fpu_invalid_set(void);
float reduce(__m128 a);
float fun(float *a)
{
__m128 c1 = _mm_set_ps1(1000);
__m128 c2 = _mm_set_ps1(1000);
for (int i=0; i < 64; i+=8) {
__m128 x1 = _mm_loadu_ps(&a[i]);
__m128 x2 = _mm_loadu_ps(&a[i+4]);
c1 = _mm_min_ps(c1, x1);
c2 = _mm_min_ps(c2, x2);
}
c1 = _mm_min_ps(c1, c2);
if (fpu_invalid_set()) {
return 1;
}
else {
return reduce(c1);
}
}
gcc -O2 -c fun.c
objdump -d fun.o
0000000000000000 <fun>:
0: 48 83 ec 28 sub $0x28,%rsp
4: 0f 28 0d 00 00 00 00 movaps 0x0(%rip),%xmm1 # b <fun+0xb>
b: 48 8d 87 00 01 00 00 lea 0x100(%rdi),%rax
12: 0f 28 c1 movaps %xmm1,%xmm0
15: 0f 1f 00 nopl (%rax)
18: 0f 10 17 movups (%rdi),%xmm2
1b: 0f 10 5f 10 movups 0x10(%rdi),%xmm3
1f: 48 83 c7 20 add $0x20,%rdi
23: 0f 5d c2 minps %xmm2,%xmm0
26: 0f 5d cb minps %xmm3,%xmm1
29: 48 39 f8 cmp %rdi,%rax
2c: 75 ea jne 18 <fun+0x18>
2e: 0f 29 44 24 10 movaps %xmm0,0x10(%rsp)
33: 0f 29 0c 24 movaps %xmm1,(%rsp)
37: e8 00 00 00 00 callq 3c <fun+0x3c> <<<<<<<<<<<< call to early
3c: 0f 28 0c 24 movaps (%rsp),%xmm1
40: 0f 28 44 24 10 movaps 0x10(%rsp),%xmm0
45: 85 c0 test %eax,%eax
47: 74 17 je 60 <fun+0x60>
49: f3 0f 10 05 00 00 00 movss 0x0(%rip),%xmm0 # 51 <fun+0x51>
50: 00
51: 48 83 c4 28 add $0x28,%rsp
55: c3 retq
56: 66 2e 0f 1f 84 00 00 nopw %cs:0x0(%rax,%rax,1)
5d: 00 00 00
60: 0f 5d c1 minps %xmm1,%xmm0 <<<<<<<<<<< min at wrong
place
63: 48 83 c4 28 add $0x28,%rsp
67: e9 00 00 00 00 jmpq 6c <fun+0x6c>
gcc 7 and earlier execute the minps instruction before calling the function
that checks the fpu state.
