| commit | a43c49f41e7cb6794e2f49abe8d14085948fe88c | [log] [tgz] |
|---|---|---|
| author | Pedro Lobo <pedro.lobo@tecnico.ulisboa.pt> | Fri Aug 22 23:23:14 2025 +0100 |
| committer | GitHub <noreply@github.com> | Fri Aug 22 23:23:14 2025 +0100 |
| tree | 3be1fb5a836daa77ca8b95444129830fe5b31f58 | |
| parent | 085d0b001674944613f61a143060350f138859e3 [diff] |
[InstCombine] Fold `(x == A) || (x & -Pow2) == A + 1` into range check (#153842)
Extends `foldAndOrOfICmpsUsingRanges` to recognize and fold idioms of
the form `(x == A) || (x & -Pow2) == A + 1`, where A + 1 is aligned to
the mask and A > |mask|.
These patterns represent a special case of contiguous range checks and
can be optimized into an addition and comparison.
```llvm
define i1 @src(i32 %x) {
%icmp1 = icmp eq i32 %x, 127
%and = and i32 %x, -32
%icmp2 = icmp eq i32 %and, 128
%ret = or i1 %icmp1, %icmp2
ret i1 %ret
}
define i1 @tgt(i32 %x) {
%1 = add i32 %x, -127
%2 = icmp ult i32 %1, 33
ret i1 %2
}
```
The same can be done for a conjunction of inequalities, of the form
`(x != A) && (x & -Pow2) != A + 1`.
```llvm
define i1 @src(i32 %x) {
%icmp1 = icmp ne i32 %x, 127
%and = and i32 %x, -32
%icmp2 = icmp ne i32 %and, 128
%result = and i1 %icmp1, %icmp2
ret i1 %result
}
define i1 @tgt(i32 %x) {
%1 = add i32 %x, -160
%2 = icmp ult i32 %1, -33
ret i1 %2
}
```
Alive2 Proof:
- Equality: https://alive2.llvm.org/ce/z/gwELqs
- Inequality: https://alive2.llvm.org/ce/z/ZPdSDt
Closes #152948.
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