https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89581
Bug ID: 89581
Summary: Unneeded stack alignment on windows x86
Product: gcc
Version: 8.2.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: yyc1992 at gmail dot com
Target Milestone: ---
On windows, when compiling the following code with ` gcc -mavx2 a.c -o - -S -O3
-g0 -fno-asynchronous-unwind-tables -fomit-frame-pointer -Wall -Wextra`
```
typedef struct {
double x1;
double x2;
} vdouble __attribute__((aligned(16)));
vdouble f(vdouble x, vdouble y)
{
return (vdouble){x.x1 + y.x1, x.x2 + y.x2};
}
```
I got
```
pushq %rbp
vmovdqa (%r8), %xmm0
movq %rcx, %rax
vaddpd (%rdx), %xmm0, %xmm0
movq %rsp, %rbp
andq $-16, %rsp
vmovaps %xmm0, (%rcx)
leave
ret
```
which include 4 extra instructions to align the stack without actually using
it....
FWIW, clang has a similar problem on linux...
https://bugs.llvm.org/show_bug.cgi?id=40844
Also worth noting that with -O2 all three vector instructions are splitted into
scalar ones whereas clang does this transformation at -O2...
