https://bugs.llvm.org/show_bug.cgi?id=43513
Bug ID: 43513
Summary: Missing 32 - __builtin_popcount(x | -x) ->
__builtin_ctz(x)
Product: libraries
Version: trunk
Hardware: PC
OS: Linux
Status: NEW
Severity: enhancement
Priority: P
Component: Transformation Utilities
Assignee: unassignedb...@nondot.org
Reporter: david.bolvan...@gmail.com
CC: llvm-bugs@lists.llvm.org
-O3 -march=haswell
int foo(int i) {
return i == 0 ? 32 : __builtin_ctz(i);
// return __builtin_ctz(i);
}
int food(int i) {
return 32 - __builtin_popcount(i | -i);
}
int foodd(int i) {
return __builtin_popcount(~i & (i-1));
}
foo(int): # @foo(int)
tzcnt eax, edi
ret
food(int): # @food(int)
mov eax, edi
neg eax
or eax, edi
popcnt ecx, eax
mov eax, 32
sub eax, ecx
ret
foodd(int): # @foodd(int)
lea eax, [rdi - 1]
andn eax, edi, eax
popcnt eax, eax
ret
https://godbolt.org/z/iNeY43
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