IR: Use an explicit map for debug info type uniquing

Rather than relying on the structural equivalence of DICompositeType to
merge type definitions, use an explicit map on the LLVMContext that
LLParser and BitcodeReader consult when constructing new nodes.
Each non-forward-declaration DICompositeType with a non-empty
'identifier:' field is stored/loaded from the type map, and the first
definiton will "win".

This map is opt-in: clients that expect ODR types from different modules
to be merged must call LLVMContext::ensureDITypeMap.

  - Clients that just happen to load more than one Module in the same
    LLVMContext won't magically merge types.

  - Clients (like LTO) that want to continue to merge types based on ODR
    identifiers should opt-in immediately.

I have updated LTOCodeGenerator.cpp, the two "linking" spots in
gold-plugin.cpp, and llvm-link (unless -disable-debug-info-type-map) to
set this.

With this in place, it will be straightforward to remove the DITypeRef
concept (i.e., referencing types by their 'identifier:' string rather
than pointing at them directly).

llvm-svn: 266549

1 files changed, 23 insertions, 10 deletions

diff --git a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp b/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
index ad14cbc998d..18386ed0727 100644
--- a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
+++ b/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
@@ -2188,16 +2188,29 @@ std::error_code BitcodeReader::parseMetadata(bool ModuleLevel) {
       if (Record.size() != 16)
         return error("Invalid record");
 
-      MetadataList.assignValue(
-          GET_OR_DISTINCT(DICompositeType, Record[0],
-                          (Context, Record[1], getMDString(Record[2]),
-                           getMDOrNull(Record[3]), Record[4],
-                           getMDOrNull(Record[5]), getMDOrNull(Record[6]),
-                           Record[7], Record[8], Record[9], Record[10],
-                           getMDOrNull(Record[11]), Record[12],
-                           getMDOrNull(Record[13]), getMDOrNull(Record[14]),
-                           getMDString(Record[15]))),
-          NextMetadataNo++);
+      // If we have a UUID and this is not a forward declaration, lookup the
+      // mapping.
+      unsigned Flags = Record[10];
+      auto *Identifier = getMDString(Record[15]);
+      DIType **MappedT = nullptr;
+      if (!(Flags & DINode::FlagFwdDecl) && Identifier)
+        MappedT = Context.getOrInsertDITypeMapping(*Identifier);
+
+      // Use the mapped type node, or create a new one if necessary.
+      DIType *CT = MappedT ? *MappedT : nullptr;
+      if (!CT) {
+        CT = GET_OR_DISTINCT(
+            DICompositeType, Record[0],
+            (Context, Record[1], getMDString(Record[2]), getMDOrNull(Record[3]),
+             Record[4], getMDOrNull(Record[5]), getMDOrNull(Record[6]),
+             Record[7], Record[8], Record[9], Flags, getMDOrNull(Record[11]),
+             Record[12], getMDOrNull(Record[13]), getMDOrNull(Record[14]),
+             Identifier));
+        if (MappedT)
+          *MappedT = CT;
+      }
+
+      MetadataList.assignValue(CT, NextMetadataNo++);
       break;
     }
     case bitc::METADATA_SUBROUTINE_TYPE: {