tree 0f1434d5d7c5710314104a6d353e1cfc713445b7
parent a5bd54307b1adacb3df297b9b8010979b9afa4d7
author Adrian Prantl <aprantl@apple.com> 1517960759 +0000
committer Adrian Prantl <aprantl@apple.com> 1517960759 +0000

Add DWARF for discriminated unions

n Rust, an enum that carries data in the variants is, essentially, a
discriminated union. Furthermore, the Rust compiler will perform
space optimizations on such enums in some situations. Previously,
DWARF for these constructs was emitted using a hack (a magic field
name); but this approach stopped working when more space optimizations
were added in https://github.com/rust-lang/rust/pull/45225.

This patch changes LLVM to allow discriminated unions to be
represented in DWARF. It adds createDiscriminatedUnionType and
createDiscriminatedMemberType to DIBuilder and then arranges for this
to be emitted using DWARF's DW_TAG_variant_part and DW_TAG_variant.

Note that DWARF requires that a discriminated union be represented as
a structure with a variant part. However, as Rust only needs to emit
pure discriminated unions, this is what I chose to expose on
DIBuilder.

Patch by Tom Tromey!

Differential Revision: https://reviews.llvm.org/D42082

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@324426 91177308-0d34-0410-b5e6-96231b3b80d8