| Issue |
96411
|
| Summary |
[PPC][AIX] Local variable needing higher alignment shows r31 not saved with r30 as required by ABI
|
| Labels |
backend:PowerPC
|
| Assignees |
|
| Reporter |
hubert-reinterpretcast
|
When a local variable requires alignment higher than 16, Clang/LLVM appears to use `r30` to hold the stack pointer on entry to the function.
As a callee-saved register, the value of `r30` is saved; however, the AIX ABI requires that callee-saved (a.k.a. "non-volatile") registers are saved from highest to lowest, meaning that `r31` should also be saved. The save of `r31` does not appear to be done (with optimization enabled) as required.
When the ABI rule is violated, the value of `r31` can be corrupted during EH unwinding.
### Source (`<stdin>`):
```cpp
struct A { char x alignas(32); };
void g(void *);
void f() {
A a;
g(&a);
}
```
### Compiler invocation:
```
clang++ --target=powerpc64-ibm-aix -O -Xclang -disable-llvm-passes -S -o - -xc++ -
```
### Compiler output (partial):
```
._Z1fv:
# %bb.0:
mflr 0
std 30, -16(1)
mr 30, 1
std 0, 16(1)
clrldi 0, 1, 59
subfic 0, 0, -192
stdux 1, 1, 0
addi 3, 1, 128
bl ._Z1gPv[PR]
nop
mr 1, 30
ld 0, 16(1)
ld 30, -16(1)
mtlr 0
blr
```
### Compiler version info (`clang++ -v`):
```
clang version 19.0.0git (https://github.com/llvm/llvm-project.git 91db7add6d72d411a50c1d7265e7d115d6e4a882)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /opt/wandbox/clang-head/bin
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/10
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/9
Selected GCC installation: /usr/lib/gcc/x86_64-linux-gnu/10
Candidate multilib: .;@m64
Selected multilib: .;@m64
```
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