https://bugs.llvm.org/show_bug.cgi?id=49028
Bug ID: 49028
Summary: Failure to optimize out test based on shr flags
Product: libraries
Version: trunk
Hardware: PC
OS: Linux
Status: NEW
Severity: enhancement
Priority: P
Component: Scalar Optimizations
Assignee: unassignedb...@nondot.org
Reporter: gabrav...@gmail.com
CC: llvm-bugs@lists.llvm.org
extern bool z;
uint16_t f(uint16_t m)
{
m >>= 1;
z = !m;
return m;
}
On x86 -O3, GCC outputs this:
f(unsigned short):
mov eax, edi
shr ax
sete BYTE PTR z[rip]
ret
LLVM outputs this:
f(unsigned short):
mov eax, edi
shr eax
test ax, ax
sete byte ptr [rip + z]
ret
The `test` seems like a net loss to me.
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