https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89680
Bug ID: 89680
Summary: Redundant moves with -march=skylake for long long
shift on 32bit x86
Product: gcc
Version: 9.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: ubizjak at gmail dot com
Target Milestone: ---
Following testcase:
--cut here--
unsigned long long
foo (unsigned long long i)
{
return i << 3;
}
--cut here--
compiles with -O2 -march=skylake -m32 to:
subl $28, %esp
movl 32(%esp), %eax
movl 36(%esp), %edx
movl %eax, (%esp)
movl %edx, 4(%esp)
vmovdqa (%esp), %xmm1
addl $28, %esp
vpsllq $3, %xmm1, %xmm0
vmovd %xmm0, %eax
vpextrd $1, %xmm0, %edx
ret
but with -O2 -march=haswell -m32 to:
vmovq 4(%esp), %xmm0
vpsllq $3, %xmm0, %xmm0
vmovd %xmm0, %eax
vpextrd $1, %xmm0, %edx
ret
The difference starts in IRA pass with:
Pass 0 for finding pseudo/allocno costs
a0 (r88,l0) best DREG, allocno DREG
a1 (r87,l0) best AREG, allocno AREG
a2 (r85,l0) best NO_REX_SSE_REGS, allocno NO_REX_SSE_REGS
- a3 (r83,l0) best NO_REX_SSE_REGS, allocno NO_REX_SSE_REGS
+ a3 (r83,l0) best NO_REGS, allocno NO_REGS
Pass 1 for finding pseudo/allocno costs
r88: preferred DREG, alternative GENERAL_REGS, allocno GENERAL_REGS
r87: preferred AREG, alternative GENERAL_REGS, allocno GENERAL_REGS
r85: preferred NO_REX_SSE_REGS, alternative NO_REGS, allocno
NO_REX_SSE_REGS
- r83: preferred NO_REX_SSE_REGS, alternative NO_REGS, allocno
NO_REX_SSE_REGS
+ r83: preferred NO_REGS, alternative NO_REGS, allocno NO_REGS
and going downhill from there.
