[llvm] r231443 - LegalizeTypes: Handle shift by 0 in ExpandShiftByConstant.

[Michael Zolotukhin]

Author: mzolotukhin
Date: Thu Mar  5 19:13:01 2015
New Revision: 231443

URL: http://llvm.org/viewvc/llvm-project?rev=231443&view=rev
Log:
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.

Added:
    llvm/trunk/test/CodeGen/X86/vec_shift7.ll
Modified:
    llvm/trunk/lib/CodeGen/SelectionDAG/LegalizeIntegerTypes.cpp

Modified: llvm/trunk/lib/CodeGen/SelectionDAG/LegalizeIntegerTypes.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/SelectionDAG/LegalizeIntegerTypes.cpp?rev=231443&r1=231442&r2=231443&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/SelectionDAG/LegalizeIntegerTypes.cpp (original)
+++ llvm/trunk/lib/CodeGen/SelectionDAG/LegalizeIntegerTypes.cpp Thu Mar  5 19:13:01 2015
@@ -1333,12 +1333,19 @@ std::pair <SDValue, SDValue> DAGTypeLega
 /// 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();

Added: llvm/trunk/test/CodeGen/X86/vec_shift7.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/vec_shift7.ll?rev=231443&view=auto
==============================================================================
--- llvm/trunk/test/CodeGen/X86/vec_shift7.ll (added)
+++ llvm/trunk/test/CodeGen/X86/vec_shift7.ll Thu Mar  5 19:13:01 2015
@@ -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