[SelectionDAG] Fix incorrect fold condition in foldSetCCWithFunnelShift.

Author: Ruhung

llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp

@@ -4462,7 +4462,8 @@ static SDValue foldSetCCWithFunnelShift(EVT VT, SDValue N0, SDValue N1,
 
   unsigned BitWidth = N0.getScalarValueSizeInBits();
   auto *ShAmtC = isConstOrConstSplat(N0.getOperand(2));
-  if (!ShAmtC || ShAmtC->getAPIntValue().uge(BitWidth))
+  APInt AmtVal = ShAmtC->getAPIntValue();
+  if (!ShAmtC || AmtVal.uge(BitWidth) || AmtVal.isZero())
     return SDValue();
 
   // Canonicalize fshr as fshl to reduce pattern-matching.

llvm/test/CodeGen/AArch64/setcc-fsh.ll

@@ -252,7 +252,8 @@ define i1 @fshl_or_ne_2(i32 %x, i32 %y) {
 define i1 @fshr_0_or_eq_0(i16 %x, i16 %y) {
 ; CHECK-LABEL: fshr_0_or_eq_0:
 ; CHECK:       // %bb.0:
-; CHECK-NEXT:    mov w0, wzr
+; CHECK-NEXT:    tst w0, #0xffff
+; CHECK-NEXT:    cset w0, eq
 ; CHECK-NEXT:    ret
   %or = or i16 %x, %y
   %f = call i16 @llvm.fshr.i16(i16 %or, i16 %x, i16 0)