[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, 3 insertions, 2 deletions

diff --git a/clang/lib/Sema/SemaLookup.cpp b/clang/lib/Sema/SemaLookup.cpp
index a41eef39edf..19df1e30423 100644
--- a/clang/lib/Sema/SemaLookup.cpp
+++ b/clang/lib/Sema/SemaLookup.cpp
@@ -1367,8 +1367,9 @@ Module *Sema::getOwningModule(Decl *Entity) {
       auto &SrcMgr = PP.getSourceManager();
       SourceLocation StartLoc =
           SrcMgr.getLocForStartOfFile(SrcMgr.getMainFileID());
-      auto &TopLevel =
-          VisibleModulesStack.empty() ? VisibleModules : VisibleModulesStack[0];
+      auto &TopLevel = ModuleScopes.empty()
+                           ? VisibleModules
+                           : ModuleScopes[0].OuterVisibleModules;
       TopLevel.setVisible(CachedFakeTopLevelModule, StartLoc);
     }