[modules] Don't emit initializers for VarDecls within a module eagerly whenever

we first touch any part of that module. Instead, defer them until the first
time that module is (transitively) imported. The initializer step for a module
then recursively initializes modules that its own headers imported.

For example, this avoids running the <iostream> global initializer in programs
that don't actually use iostreams, but do use other parts of the standard
library.

llvm-svn: 276159

1 files changed, 7 insertions, 0 deletions

diff --git a/clang/lib/Serialization/ASTReader.cpp b/clang/lib/Serialization/ASTReader.cpp
index b35bd7bd329..6bfae07b82b 100644
--- a/clang/lib/Serialization/ASTReader.cpp
+++ b/clang/lib/Serialization/ASTReader.cpp
@@ -4673,6 +4673,13 @@ ASTReader::ReadSubmoduleBlock(ModuleFile &F, unsigned ClientLoadCapabilities) {
       UnresolvedModuleRefs.push_back(Unresolved);
       break;
     }
+
+    case SUBMODULE_INITIALIZERS:
+      SmallVector<uint32_t, 16> Inits;
+      for (auto &ID : Record)
+        Inits.push_back(getGlobalDeclID(F, ID));
+      Context.addLazyModuleInitializers(CurrentModule, Inits);
+      break;
     }
   }
 }