| Issue |
63321
|
| Summary |
`(-1 + b) & x` → `select b, 0, x` should work for `!range {0, 2}` too, not just for `i1`
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
scottmcm
|
Original rust demonstration: <https://rust.godbolt.org/z/Y7n96orba>
LLVM today will simplify <https://llvm.godbolt.org/z/4jbjorjoe>
```llvm
%rhs = zext i1 %first_take to i64
%mask = add i64 -1, %rhs
%0 = and i64 %step, %mask
```
to
```llvm
%0 = select i1 %first_take, i64 0, i64 %step
```
However, if that `i1` instead comes from a `load i8` with `{0, 2}` range metadata, it no longer can: <https://llvm.godbolt.org/z/jevoe764x>
```llvm
%0 = load i8, ptr %first_take, align 1, !range !1, !noundef !2
%_5 = trunc i8 %0 to i1
%rhs = zext i1 %_5 to i64
%mask = add i64 -1, %rhs
%_6 = load i64, ptr %step, align 8
%1 = and i64 %_6, %mask
```
stays as just
```llvm
%0 = load i8, ptr %first_take, align 1, !range !0, !noundef !1
%rhs = zext i8 %0 to i64
%mask = add nsw i64 %rhs, -1
%_6 = load i64, ptr %step, align 8
%1 = and i64 %mask, %_6
```
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