[AArch64ISelLowering] Fix null pointer access in performSVEAndCombine.

[huihuiz]

Summary

When combining 'and' of an unsigned unpack and shuffle instruction,
bail early if shuffle is not constructed from a constant integer.

llvm/lib/Target/AArch64/AArch64ISelLowering.cpp

if (Opc == AArch64ISD::UUNPKHI || Opc == AArch64ISD::UUNPKLO) {
     SDValue UnpkOp = Src->getOperand(0);
     SDValue Dup = N->getOperand(1);
 
     if (Dup.getOpcode() != AArch64ISD::DUP)
       return SDValue();
 
     SDLoc DL(N);
     ConstantSDNode *C = dyn_cast<ConstantSDNode>(Dup->getOperand(0));
+    if (!C)
+      return SDValue();
+
     uint64_t ExtVal = C->getZExtValue();
 
     // If the mask is fully covered by the unpack, we don't need to push
     // a new AND onto the operand
     EVT EltTy = UnpkOp->getValueType(0).getVectorElementType();
     if ((ExtVal == 0xFF && EltTy == MVT::i8) ||
         (ExtVal == 0xFFFF && EltTy == MVT::i16) ||
         (ExtVal == 0xFFFFFFFF && EltTy == MVT::i32))

llvm/test/CodeGen/AArch64/aarch64-sve-and-combine-crash.ll

+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc -mtriple=aarch64-linux-gnu -mattr=+sve < %s | FileCheck %s
+
+target datalayout = "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128"
+target triple = "aarch64-unknown-linux-gnu"
+
+; Check that this test does not crash at performSVEAndCombine.
+
+define <vscale x 4 x i32> @test(<vscale x 8 x i16> %in1, <vscale x 4 x i32> %in2) {
+; CHECK-LABEL: test:
+; CHECK:       // %bb.0: // %entry
+; CHECK-NEXT:    uunpkhi z0.s, z0.h
+; CHECK-NEXT:    mov z1.s, s1
+; CHECK-NEXT:    and z0.d, z0.d, z1.d
+; CHECK-NEXT:    ret
+entry:
+  %i1 = call <vscale x 4 x i32> @llvm.aarch64.sve.uunpkhi.nxv4i32(<vscale x 8 x i16> %in1)
+  %i2 = shufflevector <vscale x 4 x i32> %in2, <vscale x 4 x i32> undef, <vscale x 4 x i32> zeroinitializer
+  %i3 = and <vscale x 4 x i32> %i1, %i2
+  ret <vscale x 4 x i32> %i3
+}
+
+declare <vscale x 4 x i32> @llvm.aarch64.sve.uunpkhi.nxv4i32(<vscale x 8 x i16>)