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

2 files changed, 9 insertions, 0 deletions

diff --git a/llvm/tools/gold/gold-plugin.cpp b/llvm/tools/gold/gold-plugin.cpp
index affd826e5a7..15a70a22dc6 100644
--- a/llvm/tools/gold/gold-plugin.cpp
+++ b/llvm/tools/gold/gold-plugin.cpp
@@ -1110,6 +1110,7 @@ static void thinLTOBackendTask(claimed_file &F, const void *View,
                                raw_fd_ostream *OS, unsigned TaskID) {
   // Need to use a separate context for each task
   LLVMContext Context;
+  Context.ensureDITypeMap(); // Merge debug info types.
   Context.setDiagnosticHandler(diagnosticHandlerForContext, nullptr, true);
 
   std::unique_ptr<llvm::Module> NewModule(new llvm::Module(File.name, Context));
@@ -1231,6 +1232,7 @@ static ld_plugin_status allSymbolsReadHook(raw_fd_ostream *ApiFile) {
   }
 
   LLVMContext Context;
+  Context.ensureDITypeMap(); // Merge debug info types.
   Context.setDiagnosticHandler(diagnosticHandlerForContext, nullptr, true);
 
   std::unique_ptr<Module> Combined(new Module("ld-temp.o", Context));
diff --git a/llvm/tools/llvm-link/llvm-link.cpp b/llvm/tools/llvm-link/llvm-link.cpp
index 7d02425adb8..2dac8eabaee 100644
--- a/llvm/tools/llvm-link/llvm-link.cpp
+++ b/llvm/tools/llvm-link/llvm-link.cpp
@@ -71,6 +71,10 @@ static cl::opt<bool>
 Internalize("internalize", cl::desc("Internalize linked symbols"));
 
 static cl::opt<bool>
+    DisableDITypeMap("disable-debug-info-type-map",
+                     cl::desc("Don't use a uniquing type map for debug info"));
+
+static cl::opt<bool>
 OnlyNeeded("only-needed", cl::desc("Link only needed symbols"));
 
 static cl::opt<bool>
@@ -337,6 +341,9 @@ int main(int argc, char **argv) {
   llvm_shutdown_obj Y;  // Call llvm_shutdown() on exit.
   cl::ParseCommandLineOptions(argc, argv, "llvm linker\n");
 
+  if (!DisableDITypeMap)
+    Context.ensureDITypeMap();
+
   auto Composite = make_unique<Module>("llvm-link", Context);
   Linker L(*Composite);