https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113231
Bug ID: 113231
Summary: x86_64 use MMX instructions for simple shift
operations
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: rtl-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: denis.campredon at gmail dot com
Target Milestone: ---
Compiled with -Os, the following functions use MMX instructions for simple
shift.
------------------
void foo(int *i)
{
*i *=2;
}
void bar(int *i)
{
*i <<=2;
}
void baz(int *i)
{
*i >>=2;
}
------------------
foo(int*):
movd xmm0, DWORD PTR [rdi]
pslld xmm0, 1
movd DWORD PTR [rdi], xmm0
ret
bar(int*):
movd xmm0, DWORD PTR [rdi]
pslld xmm0, 2
movd DWORD PTR [rdi], xmm0
ret
baz(int*):
movd xmm0, DWORD PTR [rdi]
psrad xmm0, 2
movd DWORD PTR [rdi], xmm0
ret
-----------------
I would expect the generated code to use "sar" or "sal" instructions like O2
uses.
The functions used to generate optimal code with version 9.5.
