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

llvm-svn: 324426

1 files changed, 8 insertions, 4 deletions

diff --git a/llvm/lib/IR/LLVMContextImpl.h b/llvm/lib/IR/LLVMContextImpl.h
index e981a806602..db7f368230d 100644
--- a/llvm/lib/IR/LLVMContextImpl.h
+++ b/llvm/lib/IR/LLVMContextImpl.h
@@ -499,18 +499,20 @@ template <> struct MDNodeKeyImpl<DICompositeType> {
   Metadata *VTableHolder;
   Metadata *TemplateParams;
   MDString *Identifier;
+  Metadata *Discriminator;
 
   MDNodeKeyImpl(unsigned Tag, MDString *Name, Metadata *File, unsigned Line,
                 Metadata *Scope, Metadata *BaseType, uint64_t SizeInBits,
                 uint32_t AlignInBits, uint64_t OffsetInBits, unsigned Flags,
                 Metadata *Elements, unsigned RuntimeLang,
                 Metadata *VTableHolder, Metadata *TemplateParams,
-                MDString *Identifier)
+                MDString *Identifier, Metadata *Discriminator)
       : Tag(Tag), Name(Name), File(File), Line(Line), Scope(Scope),
         BaseType(BaseType), SizeInBits(SizeInBits), OffsetInBits(OffsetInBits),
         AlignInBits(AlignInBits), Flags(Flags), Elements(Elements),
         RuntimeLang(RuntimeLang), VTableHolder(VTableHolder),
-        TemplateParams(TemplateParams), Identifier(Identifier) {}
+        TemplateParams(TemplateParams), Identifier(Identifier),
+        Discriminator(Discriminator) {}
   MDNodeKeyImpl(const DICompositeType *N)
       : Tag(N->getTag()), Name(N->getRawName()), File(N->getRawFile()),
         Line(N->getLine()), Scope(N->getRawScope()),
@@ -519,7 +521,8 @@ template <> struct MDNodeKeyImpl<DICompositeType> {
         Flags(N->getFlags()), Elements(N->getRawElements()),
         RuntimeLang(N->getRuntimeLang()), VTableHolder(N->getRawVTableHolder()),
         TemplateParams(N->getRawTemplateParams()),
-        Identifier(N->getRawIdentifier()) {}
+        Identifier(N->getRawIdentifier()),
+        Discriminator(N->getRawDiscriminator()) {}
 
   bool isKeyOf(const DICompositeType *RHS) const {
     return Tag == RHS->getTag() && Name == RHS->getRawName() &&
@@ -532,7 +535,8 @@ template <> struct MDNodeKeyImpl<DICompositeType> {
            RuntimeLang == RHS->getRuntimeLang() &&
            VTableHolder == RHS->getRawVTableHolder() &&
            TemplateParams == RHS->getRawTemplateParams() &&
-           Identifier == RHS->getRawIdentifier();
+           Identifier == RHS->getRawIdentifier() &&
+           Discriminator == RHS->getRawDiscriminator();
   }
 
   unsigned getHashValue() const {