[CodeGen] Keep track of decls that were deferred and have been emitted.

[junaire]

Summary

This patch adds a new field called EmittedDeferredDecls in CodeGenModule
that keeps track of decls that were deferred and have been emitted.

The intention of this patch is to solve issues in the incremental c++,
we'll lose info of decls that are lazily emitted when we undo their
usage.

See example below:

clang-repl> inline int foo() { return 42;}
clang-repl> int bar = foo();
clang-repl> %undo
clang-repl> int baz = foo();
JIT session error: Symbols not found: [ _Z3foov ]
error: Failed to materialize symbols: { (main, { baz, $.incr_module_2.inits.0,
orc_init_func.incr_module_2 }) }

Signed-off-by: Jun Zhang <[e-mail]>

[junaire]

• Rebase
• turn clang-format off in tests

[v.g.vassilev]

I am adding some more reviewers as I think this patch is ready to go.

@rjmccall, could you take a look?

[junaire]

gentle ping~

[v.g.vassilev]

I would propose to move forward with this patch. It was partially discussed in https://reviews.llvm.org/D126781 and we can rely on a post-commit review if necessary.

clang/lib/CodeGen/CodeGenModule.h

private:
   /// yet.
   llvm::DenseMap<StringRef, GlobalDecl> DeferredDecls;
 
   /// This is a list of deferred decls which we have seen that *are* actually
   /// referenced. These get code generated when the module is done.
   std::vector<GlobalDecl> DeferredDeclsToEmit;
   void addDeferredDeclToEmit(GlobalDecl GD) {
     DeferredDeclsToEmit.emplace_back(GD);
+    addEmittedDeferredDecl(GD);
+  }
+
+  /// Decls that were DeferredDecls and have now been emitted.
+  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) ||
+        llvm::GlobalValue::isWeakLinkage(L)) {
+      EmittedDeferredDecls[getMangledName(GD)] = GD;
+    }
   }
 
   /// List of alias we have emitted. Used to make sure that what they point to
   /// is defined once we get to the end of the of the translation unit.
   std::vector<GlobalDecl> Aliases;
 
   /// List of multiversion functions to be emitted. This list is processed in
   /// conjunction with other deferred symbols and is used to ensure that
assert(NewBuilder->Manglings.empty() &&
            "Newly created module should not have manglings");
     NewBuilder->Manglings = std::move(Manglings);
 
     assert(WeakRefReferences.empty() &&
            "Not all WeakRefRefs have been applied");
     NewBuilder->WeakRefReferences = std::move(WeakRefReferences);
 
     NewBuilder->TBAA = std::move(TBAA);
+
+    assert(NewBuilder->EmittedDeferredDecls.empty() &&
+           "Still have (unmerged) EmittedDeferredDecls deferred decls");
+
+    NewBuilder->EmittedDeferredDecls = std::move(EmittedDeferredDecls);
   }
 
 private:
   llvm::Constant *GetOrCreateLLVMFunction(
       StringRef MangledName, llvm::Type *Ty, GlobalDecl D, bool ForVTable,
       bool DontDefer = false, bool IsThunk = false,
       llvm::AttributeList ExtraAttrs = llvm::AttributeList(),
       ForDefinition_t IsForDefinition = NotForDefinition);

clang/lib/CodeGen/CodeGenModule.cpp

for (const GlobalDecl &GD : Aliases) {
     llvm::GlobalValue *Alias = GetGlobalValue(MangledName);
     Alias->replaceAllUsesWith(llvm::UndefValue::get(Alias->getType()));
     Alias->eraseFromParent();
   }
 }
 
 void CodeGenModule::clear() {
   DeferredDeclsToEmit.clear();
+  EmittedDeferredDecls.clear();
   if (OpenMPRuntime)
     OpenMPRuntime->clear();
 }
 
 void InstrProfStats::reportDiagnostics(DiagnosticsEngine &Diags,
                                        StringRef MainFile) {
   if (!hasDiagnostics())
     return;
for (llvm::GlobalValue &GV : M.global_values()) {
     }
 
     GV.setDLLStorageClass(llvm::GlobalValue::DefaultStorageClass);
   }
 }
 
 void CodeGenModule::Release() {
   EmitDeferred();
+  DeferredDecls.insert(EmittedDeferredDecls.begin(),
+                       EmittedDeferredDecls.end());
+  EmittedDeferredDecls.clear();
   EmitVTablesOpportunistically();
   applyGlobalValReplacements();
   applyReplacements();
   emitMultiVersionFunctions();
   EmitCXXGlobalInitFunc();
   EmitCXXGlobalCleanUpFunc();
   registerGlobalDtorsWithAtExit();
   EmitCXXThreadLocalInitFunc();

clang/test/Interpreter/code-undo.cpp

 // CHECK-NEXT: x2 = 24
 
 int foo() { return 1; }
 %undo
 int foo() { return 2; }
 auto r3 = printf("foo() = %d\n", foo());
 // CHECK-NEXT: foo() = 2
 
+inline int bar() { return 42;}
+auto r4 = bar();
+%undo
+auto r5 = bar();
+
 %quit