LegalizeTypes: Handle shift by 0 in ExpandShiftByConstant.

Though such shifts are usually optimized away by combiner, we still can
encounter them after a vector shift is legalized.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@231443 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/CodeGen/SelectionDAG/LegalizeIntegerTypes.cpp b/lib/CodeGen/SelectionDAG/LegalizeIntegerTypes.cpp
index 68ddb9e..25e80b9 100644 (file)
--- a/lib/CodeGen/SelectionDAG/LegalizeIntegerTypes.cpp
+++ b/lib/CodeGen/SelectionDAG/LegalizeIntegerTypes.cpp
@@ -1333,12 +1333,19 @@ std::pair <SDValue, SDValue> DAGTypeLegalizer::ExpandAtomic(SDNode *Node) {
 /// and the shift amount is a constant 'Amt'.  Expand the operation.
 void DAGTypeLegalizer::ExpandShiftByConstant(SDNode *N, unsigned Amt,
                                              SDValue &Lo, SDValue &Hi) {
-  assert(Amt && "Expected zero shifts to be already optimized away.");
   SDLoc DL(N);
   // Expand the incoming operand to be shifted, so that we have its parts
   SDValue InL, InH;
   GetExpandedInteger(N->getOperand(0), InL, InH);
 
+  // Though Amt shouldn't usually be 0, it's possible. E.g. when legalization
+  // splitted a vector shift, like this: <op1, op2> SHL <0, 2>.
+  if (!Amt) {
+    Lo = InL;
+    Hi = InH;
+    return;
+  }
+
   EVT NVT = InL.getValueType();
   unsigned VTBits = N->getValueType(0).getSizeInBits();
   unsigned NVTBits = NVT.getSizeInBits();

diff --git a/test/CodeGen/X86/vec_shift7.ll b/test/CodeGen/X86/vec_shift7.ll
new file mode 100644 (file)
index 0000000..cdf8289
--- /dev/null
+++ b/test/CodeGen/X86/vec_shift7.ll
@@ -0,0 +1,12 @@
+; RUN: llc < %s -march=x86 -mcpu=yonah | FileCheck %s
+
+
+; Verify that we don't fail when shift by zero is encountered.
+
+define i64 @test1(<2 x i64> %a) {
+entry:
+ %c = shl <2 x i64> %a, <i64 0, i64 2>
+ %d = extractelement <2 x i64> %c, i32 0
+ ret i64 %d
+}
+; CHECK-LABEL: test1