| Issue |
166579
|
| Summary |
[InstCombine] `llvm.ucmp` recognition/optimization issues
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
s-barannikov
|
https://gcc.godbolt.org/z/7nT7PMs93
```c
int cmp1(unsigned x, unsigned y) {
if (x != y)
return x < y ? -1 : x > y;
return 42;
}
int cmp2(unsigned x, unsigned y) {
if (x != y)
return x < y ? -1 : 1;
return 42;
}
```
`cmp2` is equivalent to `cmp1`, but `llvm.ucmp` is only recognized in `cmp1`:
```llvm
define dso_local noundef range(i32 -1, 43) i32 @cmp1(unsigned int, unsigned int)(i32 noundef %0, i32 noundef %1) local_unnamed_addr #0 {
%3 = icmp eq i32 %0, %1
%4 = tail call i32 @llvm.ucmp.i32.i32(i32 %0, i32 %1)
%5 = select i1 %3, i32 42, i32 %4
ret i32 %5
}
define dso_local noundef range(i32 -1, 43) i32 @cmp2(unsigned int, unsigned int)(i32 noundef %0, i32 noundef %1) local_unnamed_addr #0 {
%3 = icmp eq i32 %0, %1
%4 = icmp ult i32 %0, %1
%5 = select i1 %4, i32 -1, i32 1
%6 = select i1 %3, i32 42, i32 %5
ret i32 %6
}
```
---
```c
int cmp3(unsigned x, unsigned y) {
if (x != y)
return x < y ? -1 : x > y;
return 0;
}
int cmp4(unsigned x, unsigned y) {
if (x != y)
return x < y ? -1 : 1;
return 0;
}
```
These are both "canonical" `llvm.ucmp`, but `cmp3` contains a redundant `select`:
```llvm
define dso_local noundef range(i32 -1, 2) i32 @cmp3(unsigned int, unsigned int)(i32 noundef %0, i32 noundef %1) local_unnamed_addr #0 {
%3 = icmp eq i32 %0, %1
%4 = tail call i32 @llvm.ucmp.i32.i32(i32 %0, i32 %1)
%5 = select i1 %3, i32 0, i32 %4
ret i32 %5
}
define dso_local noundef range(i32 -1, 2) i32 @cmp4(unsigned int, unsigned int)(i32 noundef %0, i32 noundef %1) local_unnamed_addr #0 {
%3 = tail call i32 @llvm.ucmp.i32.i32(i32 %0, i32 %1)
ret i32 %3
}
```
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