[DAG] Fix the recognition of opaque constants in the SelectionDAGBuilder.

This fix checks the original LLVM IR node to identify opaque constants by
looking for the bitcast-constant pattern. Originally we looked at the generated
SDNode, but this might lead to incorrect results. The SDNode could have been
generated by an constant expression that was folded to a constant.

This fixes <rdar://problem/16050719>

llvm-svn: 201291

1 files changed, 7 insertions, 3 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index 3d51e9ede95..a7c99849058 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -2996,9 +2996,13 @@ void SelectionDAGBuilder::visitBitCast(const User &I) {
   if (DestVT != N.getValueType())
     setValue(&I, DAG.getNode(ISD::BITCAST, getCurSDLoc(),
                              DestVT, N)); // convert types.
-  else if(ConstantSDNode *C = dyn_cast<ConstantSDNode>(N))
-    setValue(&I, DAG.getConstant(C->getAPIntValue(), C->getValueType(0),
-                                 /*isTarget=*/false, /*isOpaque*/true));
+  // Check if the original LLVM IR Operand was a ConstantInt, because getValue()
+  // might fold any kind of constant expression to an integer constant and that
+  // is not what we are looking for. Only regcognize a bitcast of a genuine
+  // constant integer as an opaque constant.
+  else if(ConstantInt *C = dyn_cast<ConstantInt>(I.getOperand(0)))
+    setValue(&I, DAG.getConstant(C->getValue(), DestVT, /*isTarget=*/false,
+                                 /*isOpaque*/true));
   else
     setValue(&I, N);            // noop cast.
 }