| Issue |
133928
|
| Summary |
miscompile from AArch64 backend
|
| Labels |
backend:AArch64,
llvm:codegen,
miscompilation
|
| Assignees |
|
| Reporter |
regehr
|
take this function:
```llvm
define i4 @f(ptr %0, i8 %1, i1 %2) {
%4 = trunc i8 %1 to i4
%5 = getelementptr i8, ptr %0, i8 %1
%6 = icmp uge ptr %5, %0
br i1 %6, label %common.ret, label %7
common.ret: ; preds = %10, %7, %3
%common.ret.op = phi i4 [ 0, %10 ], [ 1, %3 ], [ 0, %7 ]
ret i4 %common.ret.op
7: ; preds = %3
%8 = add nuw i8 0, 0
%9 = icmp ult i8 %8, %1
br i1 %2, label %common.ret, label %10
10: ; preds = %7
%11 = udiv i4 1, 1
br label %common.ret
}
```
when invoked like this `f((char *)0xd, -5, 0)`, Alive believes that it should return 0, and I agree:
%5 = 0x8
%6 = false
branch to label %7
branch to label %10
branch to label %common.ret
return 0
on the other hand, the AArch64 backend is giving this:
```
~/reduce$ ~/llvm-project/for-alive/bin/llc -march=aarch64 -o - reduced.ll
.build_version macos, 15, 0
.section __TEXT,__text,regular,pure_instructions
.globl _f ; -- Begin function f
.p2align 2
_f: ; @f
.cfi_startproc
; %bb.0:
add x8, x0, w1, uxtb
cmp x8, x0
b.lo LBB0_2
; %bb.1:
mov w0, #1 ; =0x1
ret
LBB0_2:
mov w0, wzr
ret
.cfi_endproc
; -- End function
.subsections_via_symbols
~/reduce$
```
which returns 1 when called with those same arguments. it looks like maybe the add should be sxtb instead of uxtb since GEP offsets are signed?
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