PR12145: Avoid emitting loads of constexpr variables in contexts where there

is no odr-use of the variable. Go slightly beyond what the standard requires
for variables of reference type.

llvm-svn: 151879

1 files changed, 15 insertions, 9 deletions

diff --git a/clang/lib/CodeGen/CGExprScalar.cpp b/clang/lib/CodeGen/CGExprScalar.cpp
index 125e431bff0..f7ab880e6cd 100644
--- a/clang/lib/CodeGen/CGExprScalar.cpp
+++ b/clang/lib/CodeGen/CGExprScalar.cpp
@@ -212,18 +212,21 @@ public:
   // l-values.
   Value *VisitDeclRefExpr(DeclRefExpr *E) {
     Expr::EvalResult Result;
-    if (!E->EvaluateAsRValue(Result, CGF.getContext()))
-      return EmitLoadOfLValue(E);
+    bool IsReferenceConstant = false;
+    QualType EvalTy = E->getType();
+    if (!E->EvaluateAsRValue(Result, CGF.getContext())) {
+      // If this is a reference, try to determine what it is bound to.
+      if (!E->getDecl()->getType()->isReferenceType() ||
+          !E->EvaluateAsLValue(Result, CGF.getContext()))
+        return EmitLoadOfLValue(E);
+
+      IsReferenceConstant = true;
+      EvalTy = E->getDecl()->getType();
+    }
 
     assert(!Result.HasSideEffects && "Constant declref with side-effect?!");
 
-    llvm::Constant *C;
-    if (Result.Val.isInt())
-      C = Builder.getInt(Result.Val.getInt());
-    else if (Result.Val.isFloat())
-      C = llvm::ConstantFP::get(VMContext, Result.Val.getFloat());
-    else
-      return EmitLoadOfLValue(E);
+    llvm::Constant *C = CGF.CGM.EmitConstantValue(Result.Val, EvalTy, &CGF);
 
     // Make sure we emit a debug reference to the global variable.
     if (VarDecl *VD = dyn_cast<VarDecl>(E->getDecl())) {
@@ -233,6 +236,9 @@ public:
       CGF.EmitDeclRefExprDbgValue(E, C);
     }
 
+    if (IsReferenceConstant)
+      return EmitLoadOfLValue(CGF.MakeNaturalAlignAddrLValue(C, E->getType()));
+
     return C;
   }
   Value *VisitObjCSelectorExpr(ObjCSelectorExpr *E) {