https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89676
Bug ID: 89676
Summary: Redundant moves for long long shift on 32bit x86
Product: gcc
Version: 9.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: rtl-optimization
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 for 32bit x86 to (-O2):
pushl %ebx
movl 8(%esp), %ecx
movl 12(%esp), %ebx
movl %ecx, %eax
movl %ebx, %edx
popl %ebx
shldl $3, %eax, %edx
sall $3, %eax
ret
There is unnecessary move to %ecx/%ebx pair in the above code.
Clang creates:
movl 4(%esp), %eax
movl 8(%esp), %edx
shldl $3, %eax, %edx
shll $3, %eax
retl
