https://bugs.llvm.org/show_bug.cgi?id=42197
Bug ID: 42197
Summary: Canonicalize OR with operands which do not have shared
bits to ADD
Product: libraries
Version: trunk
Hardware: PC
OS: Linux
Status: NEW
Severity: enhancement
Priority: P
Component: Scalar Optimizations
Assignee: unassignedb...@nondot.org
Reporter: david.bolvan...@gmail.com
CC: llvm-bugs@lists.llvm.org
typedef unsigned char byte;
byte add_no_common_bits(byte x, byte y) {
// hint, no common bits
__builtin_assume((x & y) == 0);
return x | y;
}
byte or_no_common_bits(byte x, byte y) {
// hint, no common bits
__builtin_assume((x & y) == 0);
return x + y;
}
add_no_common_bits(unsigned char, unsigned char):
mov eax, edi
or eax, esi
ret
or_no_common_bits(unsigned char, unsigned char):
lea eax, [rsi + rdi]
ret
If we can prove that there are no shared bits between X and Y, maybe we could
turn OR to ADD.
Or ADD to OR.. not sure which form is better.
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