[DAG] Fix an assertion failure caused by an invalid cast in method 'BuildVectorSDNode::isConstantSplat'

This patch renames method 'isConstantSplat' as 'getConstantSplatValue'
(mainly for consistency reasons), and rewrites its logic to ensure
that we always perform a legal 'cast<ConstantSDNode>'.

Added test shift-combine-crash.ll to verify that DAGCombiner no longer crashes with an assertion failure in the attempt to simplify a vector shift by a vector of all undef counts.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@204536 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 5 insertions, 4 deletions

diff --git a/include/llvm/CodeGen/SelectionDAGNodes.h b/include/llvm/CodeGen/SelectionDAGNodes.h
index a6c72ca2d1..fd915b01d6 100644
--- a/include/llvm/CodeGen/SelectionDAGNodes.h
+++ b/include/llvm/CodeGen/SelectionDAGNodes.h
@@ -1522,10 +1522,11 @@ public:
                        unsigned MinSplatBits = 0,
                        bool isBigEndian = false) const;
 
-  /// isConstantSplat - Simpler form of isConstantSplat. Get the constant splat
-  /// when you only care about the value. Returns nullptr if this isn't a
-  /// constant splat vector.
-  ConstantSDNode *isConstantSplat() const;
+  /// getConstantSplatValue - Check if this is a constant splat, and if so,
+  /// return the splat value only if it is a ConstantSDNode. Otherwise
+  /// return nullptr. This is a simpler form of isConstantSplat.
+  /// Get the constant splat only if you care about the splat value.
+  ConstantSDNode *getConstantSplatValue() const;
 
   bool isConstant() const;