ayzhao added inline comments.
================
Comment at: clang/lib/Sema/SemaInit.cpp:4151
+ QualType T = Entity.getType();
+ // FIXME: Union is unsupported.
+ int InitKind = T->isArrayType() ? 0 : 4;
----------------
ayzhao wrote:
> ayzhao wrote:
> > Hmm...it seems like as is this patch generates the correct code for
> > parentheses-initialized `union`s:
> >
> > ```
> > % cat ~/src/tests/test-union.cc
> > union C {
> > float a;
> > double b;
> > };
> >
> >
> > C foo() {
> > return C(1);
> > }
> >
> > % bin/clang++ -std=c++20 -emit-llvm -S -c -o - ~/src/tests/test-union.cc
> > ; ModuleID = '/usr/local/google/home/ayzhao/src/tests/test-union.cc'
> > source_filename = "/usr/local/google/home/ayzhao/src/tests/test-union.cc"
> > target datalayout =
> > "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
> > target triple = "x86_64-unknown-linux-gnu"
> >
> > %union.C = type { double }
> >
> > ; Function Attrs: mustprogress noinline nounwind optnone uwtable
> > define dso_local double @_Z3foov() #0 {
> > entry:
> > %retval = alloca %union.C, align 8
> > store float 1.000000e+00, ptr %retval, align 8
> > %coerce.dive = getelementptr inbounds %union.C, ptr %retval, i32 0, i32 0
> > %0 = load double, ptr %coerce.dive, align 8
> > ret double %0
> > }
> >
> > attributes #0 = { mustprogress noinline nounwind optnone uwtable
> > "frame-pointer"="all" "min-legal-vector-width"="0"
> > "no-trapping-math"="true" "stack-protector-buffer-size"="8"
> > "target-cpu"="x86-64" "target-features"="+cx8,+fxsr,+mmx,+sse,+sse2,+x87"
> > "tune-cpu"="generic" }
> >
> > !llvm.linker.options = !{}
> > !llvm.module.flags = !{!0, !1, !2, !3, !4}
> > !llvm.ident = !{!5}
> >
> > !0 = !{i32 1, !"wchar_size", i32 4}
> > !1 = !{i32 8, !"PIC Level", i32 2}
> > !2 = !{i32 7, !"PIE Level", i32 2}
> > !3 = !{i32 7, !"uwtable", i32 2}
> > !4 = !{i32 7, !"frame-pointer", i32 2}
> > !5 = !{!"clang version 16.0.0"}
> > ```
> >
> > I'm guessing this comment is specific to error messages.
> OK, I see what's going on. The following program fails to build:
>
> ```
> #include <string>
>
> union C {
> int a;
> std::string b;
> };
>
>
> C foo() {
> return C("Hello, World!");
> }
> ```
>
Actually, it turns out that the above example program is ill-formed because in
a non-designated brace initialization, the parameter initializes the first
element.
OTOH, there is a bug where
```
C(1, "Hello, World!");
```
compiles without errors because we check that # of parameters <= # of fields.
There may also be issues with anonymous `union`s in `struct`s - I'll have to
investigate this further.
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D129531/new/
https://reviews.llvm.org/D129531
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