| Issue |
104794
|
| Summary |
For tail calls, clang generates extra alloca for sret parameter on 32 bit targets
|
| Labels |
clang,
clang:codegen
|
| Assignees |
kiran-isaac
|
| Reporter |
kiran-isaac
|
While running a fuzzer to verify #102896, I kept getting errors for any cases using `double _Complex` or `_BitInt(n>64)` as return types for `[[clang::musttail]]` functions on 32 bit targets. These cases would compile such that new memory is `alloca`'d for the sret parameter, rather than passing through the same sret ptr from the caller. For example
```cpp
double _Complex F11(signed short P0);
double _Complex F12(signed short P0) {
[[clang::musttail]] return F11(1000);
}
```
```bash
clang -S -emit-llvm --target=(arm/x86/any 32 bit target) -o -
```
Gives you (see #104770 for more info about weird no predecessors block):
```llvm
; Function Attrs: mustprogress noinline optnone
define dso_local arm_aapcscc void @_Z3F12s(ptr dead_on_unwind noalias writable sret({ double, double }) align 8 %agg.result, i16 noundef signext %P0) #0 {
entry:
%P0.addr = alloca i16, align 2
%tmp = alloca { double, double }, align 8
store i16 %P0, ptr %P0.addr, align 2
%0 = load i16, ptr %P0.addr, align 2
musttail call arm_aapcscc void @_Z3F11s(ptr dead_on_unwind writable sret({ double, double }) align 8 %tmp, i16 noundef signext %0)
ret void
1: ; No predecessors!
...
ret void
}
```
This is an invalid tail call. Similar behaviour can be observed when replacing `double _Complex` with `_BitInt(N>64)`.
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