| Issue |
137114
|
| Summary |
Missed optimizations on code that compares integer sign bits
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
MagentaTreehouse
|
Given this code:
```c++
bool diffSignBit(int x, int y) {
return x < 0 && y >= 0 || x >= 0 && y < 0;
}
```
Output with `-O3`:
```llvm
define dso_local noundef zeroext i1 @diffSignBit(int, int)(i32 noundef %x, i32 noundef %y) local_unnamed_addr {
entry:
%cmp = icmp slt i32 %x, 0
%cmp1 = icmp sgt i32 %y, -1
%or.cond = and i1 %cmp, %cmp1
br i1 %or.cond, label %lor.end, label %lor.rhs
lor.rhs:
%cmp2 = icmp sgt i32 %x, -1
%cmp3 = icmp slt i32 %y, 0
%0 = and i1 %cmp2, %cmp3
br label %lor.end
lor.end:
%1 = phi i1 [ %0, %lor.rhs ], [ true, %entry ]
ret i1 %1
}
```
If it is written as the equivalent of `!sameSignBit(x, y)`,
```c++
bool diffSignBit(int x, int y) {
return !(x >= 0 && y >= 0 || x < 0 && y < 0);
}
```
... we get the desired output:
```llvm
define dso_local noundef zeroext i1 @diffSignBit(int, int)(i32 noundef %x, i32 noundef %y) local_unnamed_addr {
entry:
%0 = xor i32 %y, %x
%lnot = icmp slt i32 %0, 0
ret i1 %lnot
}
```
See:
https://compiler-explorer.com/z/vWv38bGzT
https://alive2.llvm.org/ce/z/VWL1FE
![]()
_______________________________________________
llvm-bugs mailing list
llvm-bugs@lists.llvm.org
https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-bugs
