| Issue |
165291
|
| Summary |
[X86] Failure to merge BT with matching BTC/BTR/BTS
|
| Labels |
backend:X86,
missed-optimization
|
| Assignees |
|
| Reporter |
RKSimon
|
```ll
define i1 @btr_eq_i32(ptr %word, i32 %position) nounwind {
%ofs = and i32 %position, 31
%bit = shl nuw i32 1, %ofs
%mask = xor i32 %bit, -1
%ld = load i32, ptr %word
%test = and i32 %ld, %bit
%res = and i32 %ld, %mask
%cmp = icmp eq i32 %test, 0
store i32 %res, ptr %word
ret i1 %cmp
}
```
```asm
btr_eq_i32: # @btr_eq_i32
movl (%rdi), %eax
movl %eax, %ecx
btrl %esi, %ecx
btl %esi, %eax
setae %al
movl %ecx, (%rdi)
retq
```
The BTR sets the same EFLAGS CF result as BT (it then clear the bit value afterward) - so we could perform this as:
```asm
btr_eq_i32: # @btr_eq_i32
movl (%rdi), %eax
btrl %esi, %eax
movl %eax, (%rdi)
setae %al
retq
```
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