| Issue |
134540
|
| Summary |
Missed optimization when using `llvm.assume`, although scalar-evolution can use it to figure out the range.
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
GINN-Imp
|
Missed optimization: `store i1 %0, ptr @a, align 1` --> `store i1 true, ptr @a, align 1`
```llvm
@a = external global i1
define i1 @src(ptr %G) {
BB:
%L = load i1, ptr %G, align 1
%0 = xor i1 %L, true
store i1 %0, ptr @a, align 1
call void @llvm.assume(i1 %0)
ret i1 %0
}
```
clang-trunk -O3 generates:
```llvm
define noundef i1 @src(ptr readonly captures(none) %G) local_unnamed_addr #0 {
%L = load i1, ptr %G, align 1
%0 = xor i1 %L, true
store i1 %0, ptr @a, align 1
tail call void @llvm.assume(i1 %0)
ret i1 true
}
```
We found that `scalar-evolution` looked like it could do some analysis with llvm.assume (it found that the value of `%L` was `false`), but the optimization was still missed:
```
Printing analysis 'Scalar Evolution Analysis' for function 'src':
Classifying expressions for: @src
%L = load i1, ptr %G, align 1
--> %L U: [0,-1) S: [0,-1)
```
Godbolt: https://godbolt.org/z/bd9fEGe18
Alive2 proof: https://alive2.llvm.org/ce/z/AYhVHx
The reduced IR is derived from https://github.com/torvalds/linux/blob/master/mm/page_alloc.c
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