https://bugs.llvm.org/show_bug.cgi?id=48768
Bug ID: 48768
Summary: Failure to optimize using flags from blsi
Product: libraries
Version: trunk
Hardware: PC
OS: Linux
Status: NEW
Severity: enhancement
Priority: P
Component: Scalar Optimizations
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
int f(unsigned long x)
{
return 0 >= (int)(-x & x);
}
With -O3 -mbmi, GCC emits this:
f(unsigned long):
xor eax, eax
blsi edi, edi
setle al
ret
LLVM emits this:
f(unsigned long): # @f(unsigned long)
blsi ecx, edi
xor eax, eax
test ecx, ecx
setle al
ret
The usage of the `test` instruction is useless as the flags from `blsi` can
directly be used.
See also Godbolt comparison here : https://godbolt.org/z/dqb18e
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