Introduce a new cast kind for an "lvalue bitcast", which handles

reinterpret_casts (possibly indirectly via C-style/functional casts)
on values, e.g., 

  int i;
  reinterpret_cast<short&>(i);

The IR generated for this is essentially the same as for

  *reinterpret_cast<short*>(&i).

Fixes PR6437, PR7593, and PR7344. 

llvm-svn: 108294

3 files changed, 15 insertions, 1 deletions

diff --git a/clang/lib/CodeGen/CGExpr.cpp b/clang/lib/CodeGen/CGExpr.cpp
index 0426a60f0c3..5a4808bce9d 100644
--- a/clang/lib/CodeGen/CGExpr.cpp
+++ b/clang/lib/CodeGen/CGExpr.cpp
@@ -1816,7 +1816,8 @@ LValue CodeGenFunction::EmitCastLValue(const CastExpr *E) {
     
     return LValue::MakeAddr(Derived, MakeQualifiers(E->getType()));
   }
-  case CastExpr::CK_BitCast: {
+  case CastExpr::CK_BitCast: 
+  case CastExpr::CK_LValueBitCast: {
     // This must be a reinterpret_cast (or c-style equivalent).
     const ExplicitCastExpr *CE = cast<ExplicitCastExpr>(E);
     
diff --git a/clang/lib/CodeGen/CGExprAgg.cpp b/clang/lib/CodeGen/CGExprAgg.cpp
index 20722f7799c..219a5f91532 100644
--- a/clang/lib/CodeGen/CGExprAgg.cpp
+++ b/clang/lib/CodeGen/CGExprAgg.cpp
@@ -307,6 +307,10 @@ void AggExprEmitter::VisitCastExpr(CastExpr *E) {
     break;
   }
       
+  case CastExpr::CK_LValueBitCast:
+    llvm_unreachable("there are no lvalue bit-casts on aggregates");
+    break;
+      
   case CastExpr::CK_BitCast: {
     // This must be a member function pointer cast.
     Visit(E->getSubExpr());
diff --git a/clang/lib/CodeGen/CGExprScalar.cpp b/clang/lib/CodeGen/CGExprScalar.cpp
index 1ebc2c571a0..ef38209e1ea 100644
--- a/clang/lib/CodeGen/CGExprScalar.cpp
+++ b/clang/lib/CodeGen/CGExprScalar.cpp
@@ -925,6 +925,15 @@ Value *ScalarExprEmitter::EmitCastExpr(CastExpr *CE) {
     //assert(0 && "Unknown cast kind!");
     break;
 
+  case CastExpr::CK_LValueBitCast: {
+    Value *V = EmitLValue(E).getAddress();
+    V = Builder.CreateBitCast(V, 
+                          ConvertType(CGF.getContext().getPointerType(DestTy)));
+    // FIXME: Are the qualifiers correct here?
+    return EmitLoadOfLValue(LValue::MakeAddr(V, CGF.MakeQualifiers(DestTy)), 
+                            DestTy);
+  }
+      
   case CastExpr::CK_AnyPointerToObjCPointerCast:
   case CastExpr::CK_AnyPointerToBlockPointerCast:
   case CastExpr::CK_BitCast: {