[CodeGen] Unique constant CompoundLiterals.

Our newly aggressive constant folding logic makes it possible for
CGExprConstant to see the same CompoundLiteralExpr more than once. So,
emitting a new GlobalVariable every time we see a CompoundLiteral is no
longer correct.

We had a similar issue with BlockExprs that was caught while testing
said aggressive folding, so I applied the same style of fix (see D26410)
here. If we find yet another case where this needs to happen, we should
probably refactor this so we don't have a third DenseMap+getter+setter.

As a design note: getAddrOfConstantCompoundLiteralIfEmitted is really
only intended to be called by ConstExprEmitter::EmitLValue. So,
returning a GlobalVariable* instead of a ConstantAddress costs us
effectively nothing, and saves us either a few bytes per entry in our
map or a bit of code duplication.

llvm-svn: 290661

1 files changed, 14 insertions, 0 deletions

diff --git a/clang/lib/CodeGen/CodeGenModule.h b/clang/lib/CodeGen/CodeGenModule.h
index 5f06ba9..1d72b4e 100644
--- a/clang/lib/CodeGen/CodeGenModule.h
+++ b/clang/lib/CodeGen/CodeGenModule.h
@@ -455,6 +455,10 @@ private:
   bool isTriviallyRecursive(const FunctionDecl *F);
   bool shouldEmitFunction(GlobalDecl GD);
 
+  /// Map used to be sure we don't emit the same CompoundLiteral twice.
+  llvm::DenseMap<const CompoundLiteralExpr *, llvm::GlobalVariable *>
+      EmittedCompoundLiterals;
+
   /// Map of the global blocks we've emitted, so that we don't have to re-emit
   /// them if the constexpr evaluator gets aggressive.
   llvm::DenseMap<const BlockExpr *, llvm::Constant *> EmittedGlobalBlocks;
@@ -824,6 +828,16 @@ public:
   /// compound literal expression.
   ConstantAddress GetAddrOfConstantCompoundLiteral(const CompoundLiteralExpr*E);
 
+  /// If it's been emitted already, returns the GlobalVariable corresponding to
+  /// a compound literal. Otherwise, returns null.
+  llvm::GlobalVariable *
+  getAddrOfConstantCompoundLiteralIfEmitted(const CompoundLiteralExpr *E);
+
+  /// Notes that CLE's GlobalVariable is GV. Asserts that CLE isn't already
+  /// emitted.
+  void setAddrOfConstantCompoundLiteral(const CompoundLiteralExpr *CLE,
+                                        llvm::GlobalVariable *GV);
+
   /// \brief Returns a pointer to a global variable representing a temporary
   /// with static or thread storage duration.
   ConstantAddress GetAddrOfGlobalTemporary(const MaterializeTemporaryExpr *E,