| Issue |
60645
|
| Summary |
AArch64 backend miscompiles testcase of pre-dec addressing mode with constant offset
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
huihzhang
|
Use reduced test ir below:
```llvm
define i8* @test(i8* %ptr, i64 %t0) {
%t1 = add nuw nsw i64 %t0, 8
%t2 = mul i64 %t1, -4
%t3 = getelementptr i8, i8* %ptr, i64 %t2
%t4 = bitcast i8* %t3 to i32*
store i32 0, i32* %t4, align 4
%t5 = shl i64 %t1, 2
%t6 = sub nuw nsw i64 -8, %t5
%t7 = getelementptr i8, i8* %ptr, i64 %t6
%t8 = bitcast i8* %t7 to i32*
store i32 0, i32* %t8, align 4
ret i8* %ptr
}
```
Run with: llc -mtriple=aarch64 < t.ll
```
test: // @test
.cfi_startproc
// %bb.0:
sub x8, x0, x1, lsl #2
str wzr, [x8, #32]! // wrong
stur wzr, [x8, #-8]
ret
```
The first str is not generated right. It's pre-dec addressing, offset should be -32.
```
str wzr, [x8, #-32]! // Expect -32 as offset.
```
Also note that this bug was exposed by https://reviews.llvm.org/D120216
Prior to D120216, we were generating correct code without auto-decreasing base address x8.
```
// %bb.0:
sub x8, x0, x1, lsl #2
stur wzr, [x8, #-32]
stur wzr, [x8, #-40]
ret
```
![]()
_______________________________________________
llvm-bugs mailing list
[email protected]
https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-bugs
