[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, 6 insertions, 7 deletions

diff --git a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index df8d423ab2..029011cffc 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -6573,15 +6573,14 @@ bool BuildVectorSDNode::isConstantSplat(APInt &SplatValue,
   return true;
 }
 
-ConstantSDNode *BuildVectorSDNode::isConstantSplat() const {
+ConstantSDNode *BuildVectorSDNode::getConstantSplatValue() const {
   SDValue Op0 = getOperand(0);
-  for (unsigned i = 0, e = getNumOperands(); i != e; ++i) {
-    SDValue Opi = getOperand(i);
-    unsigned Opc = Opi.getOpcode();
-    if ((Opc != ISD::UNDEF && Opc != ISD::Constant && Opc != ISD::ConstantFP) ||
-        Opi != Op0)
+  if (Op0.getOpcode() != ISD::Constant)
+    return nullptr;
+
+  for (unsigned i = 1, e = getNumOperands(); i != e; ++i)
+    if (getOperand(i) != Op0)
       return nullptr;
-  }
 
   return cast<ConstantSDNode>(Op0);
 }