[CodeGen] Clean up access to EmittedDeferredDecls, NFCI.

GlobalDecls should only be added to EmittedDeferredDecls if they
need reemission. This is checked in addEmittedDeferredDecl, which
is called via addDeferredDeclToEmit. Extend these checks to also
handle VarDecls (for lambdas, as tested in Interpreter/lambda.cpp)
and remove the direct access of EmittedDeferredDecls in EmitGlobal
that may actually end up duplicating FunctionDecls.

Differential Revision: https://reviews.llvm.org/D156897

(cherry picked from commit b719e41)

Author: hahnjo

clang/lib/CodeGen/CodeGenModule.cpp

@@ -3664,7 +3664,6 @@ void CodeGenModule::EmitGlobal(GlobalDecl GD) {
     // The value must be emitted, but cannot be emitted eagerly.
     assert(!MayBeEmittedEagerly(Global));
     addDeferredDeclToEmit(GD);
-    EmittedDeferredDecls[MangledName] = GD;
   } else {
     // Otherwise, remember that we saw a deferred decl with this name.  The
     // first use of the mangled name will cause it to move into
@@ -4404,7 +4403,6 @@ llvm::Constant *CodeGenModule::GetOrCreateLLVMFunction(
       // DeferredDeclsToEmit list, and remove it from DeferredDecls (since we
       // don't need it anymore).
       addDeferredDeclToEmit(DDI->second);
-      EmittedDeferredDecls[DDI->first] = DDI->second;
       DeferredDecls.erase(DDI);
 
       // Otherwise, there are cases we have to worry about where we're
@@ -4685,7 +4683,6 @@ CodeGenModule::GetOrCreateLLVMGlobal(StringRef MangledName, llvm::Type *Ty,
     // Move the potentially referenced deferred decl to the DeferredDeclsToEmit
     // list, and remove it from DeferredDecls (since we don't need it anymore).
     addDeferredDeclToEmit(DDI->second);
-    EmittedDeferredDecls[DDI->first] = DDI->second;
     DeferredDecls.erase(DDI);
   }
 

clang/lib/CodeGen/CodeGenModule.h

@@ -361,10 +361,15 @@ class CodeGenModule : public CodeGenTypeCache {
   llvm::DenseMap<llvm::StringRef, GlobalDecl> EmittedDeferredDecls;
 
   void addEmittedDeferredDecl(GlobalDecl GD) {
-    if (!llvm::isa<FunctionDecl>(GD.getDecl()))
-      return;
-    llvm::GlobalVariable::LinkageTypes L = getFunctionLinkage(GD);
-    if (llvm::GlobalValue::isLinkOnceLinkage(L) ||
+    // Assume a linkage by default that does not need reemission.
+    auto L = llvm::GlobalValue::ExternalLinkage;
+    if (llvm::isa<FunctionDecl>(GD.getDecl()))
+      L = getFunctionLinkage(GD);
+    else if (auto *VD = llvm::dyn_cast<VarDecl>(GD.getDecl()))
+      L = getLLVMLinkageVarDefinition(VD);
+
+    if (llvm::GlobalValue::isInternalLinkage(L) ||
+        llvm::GlobalValue::isLinkOnceLinkage(L) ||
         llvm::GlobalValue::isWeakLinkage(L)) {
       EmittedDeferredDecls[getMangledName(GD)] = GD;
     }