| Issue |
55484
|
| Summary |
miscompile from multiple backends
|
| Labels |
backend:AArch64,
llvm:codegen,
miscompilation
|
| Assignees |
|
| Reporter |
regehr
|
here's a function:
```llvm
define i32 @f(i32 %0) {
%2 = lshr i32 %0, 8
%3 = shl i32 %0, 8
%4 = or i32 %2, %3
%5 = trunc i32 %4 to i16
%6 = sext i16 %5 to i32
ret i32 %6
}
```
we believe that `f(0x00800000) -> ffff8000` but the top-of-tree arm64, x86, and x86-64 backends are all emitting code which says that `f(0x00800000) -> 0`
```console
Johns-MacBook-Pro:~ regehr$ llc -o - foo.ll
.section __TEXT,__text,regular,pure_instructions
.build_version macos, 12, 0
.globl _f ; -- Begin function f
.p2align 2
_f: ; @f
.cfi_startproc
; %bb.0:
rev w8, w0
asr w0, w8, #16
ret
.cfi_endproc
; -- End function
.subsections_via_symbols
Johns-MacBook-Pro:~ regehr$
```
cc @ornata @nunoplopes @ryan-berger @nbushehri @zhengyang92 @aqjune @Hatsunespica
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