[X86] Return UNDEF from LowerScalarImmediateShift when the shift amount is out of range.

I think we only turn out of range shiftss to undef when
all elements are out of range or the shift amount is a splat out
of range. I'm not sure which, I didn't check.

During lowering we can split a shift where some elements
are out of range into multiple shifts. This can create a
new shift with a splat shift amount that is out of range.

This patch returns undef for this case.

Fixes PR42615.

Differential Revision: https://reviews.llvm.org/D64699

llvm-svn: 366096

1 files changed, 5 insertions, 2 deletions

diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index c5bf3dcac45..47389f2df32 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -25033,8 +25033,11 @@ static SDValue LowerScalarImmediateShift(SDValue Op, SelectionDAG &DAG,
   APInt APIntShiftAmt;
   if (!isConstantSplat(Amt, APIntShiftAmt))
     return SDValue();
-  assert(APIntShiftAmt.ult(VT.getScalarSizeInBits()) &&
-         "Out of range shift amount");
+
+  // If the shift amount is out of range, return undef.
+  if (APIntShiftAmt.uge(VT.getScalarSizeInBits()))
+    return DAG.getUNDEF(VT);
+
   uint64_t ShiftAmt = APIntShiftAmt.getZExtValue();
 
   if (SupportedVectorShiftWithImm(VT, Subtarget, Op.getOpcode()))