hubert.reinterpretcast added inline comments.
================
Comment at: clang/test/CodeGen/init.c:197
// CHECK-LABEL: @nonzeroPaddedUnionMemset(
- // CHECK-NOT: store
- // CHECK-NOT: memcpy
- // CHECK: call void @llvm.memset.p0i8.i32(i8* {{.*}}, i8 -16, i32 36, i1
false)
+ // CHECK: call void @llvm.memcpy.p0i8.p0i8.i32(i8* align 4 {{.*}}, i8* align
4 {{.*}} [[INIT_PADDEDUNION]], {{.*}}, i32 36, i1 false)
}
----------------
vitalybuka wrote:
> vitalybuka wrote:
> > hubert.reinterpretcast wrote:
> > > This is C++ aggregate initialization and not value-initialization. The
> > > wording you quoted from the C++ standard is for zero-initialization,
> > > which might be part of value initialization, but you have not shown that
> > > aggregate initialization of a union involves zero-initialization of that
> > > union.
> > reading this more I don't see any evidence that either C++ or C requires
> > padding initialization.
> > Reading this I expect that all function here should be equivalent
> > https://godbolt.org/z/1O_9-e
> > But they are not. Clang and GCC initialized padding after the first member.
> So if go trough "aggregates" then nothing is said about padding in union.
> If we go trough "list-initialization" then value initialization should be
> applied, part of which is zero initialization.
> If so union padding should be initialized.
>
>
In C++14, the list in [dcl.init.list] starts with:
If T is an aggregate, aggregate initialization is performed.
The bullet in C++17 follows only a case for copying and then a case for string
literals.
The bullet in the C++2a CD likewise, with an additional earlier bullet that
also becomes aggregate initialization.
It is in C++11 where an empty list gets value-initialization treatment, and the
next bullet goes to aggregate initialization.
The inline comment was not added to an empty list case.
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D68115/new/
https://reviews.llvm.org/D68115
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