[AArch64] Fix crash in LowerBUILD_VECTOR trying to create invalid EXTRACT_SUBVECTOR.

[aemerson]

Summary

This fixes and assertion and miscompile due to falling through to the code that tries to use EXTRACT_SUBVECTOR, even when we bailed out due to having a non-constant extract operand.

rdar://106096671

[dmgreen]

Sounds good to me.

llvm/lib/Target/AArch64/AArch64ISelLowering.cpp

if (AllLanesExtractElt) {
     SDNode *Vector = nullptr;
     bool Even = false;
     bool Odd = false;
     // Check whether the extract elements match the Even pattern <0,2,4,...> or
     // the Odd pattern <1,3,5,...>.
     for (unsigned i = 0; i < NumElts; ++i) {
       SDValue V = Op.getOperand(i);
       const SDNode *N = V.getNode();
-      if (!isa<ConstantSDNode>(N->getOperand(1)))
+      if (!isa<ConstantSDNode>(N->getOperand(1))) {
+        Even = false;
+        Odd = false;
         break;
+      }
       SDValue N0 = N->getOperand(0);
 
       // All elements are extracted from the same vector.
       if (!Vector) {
         Vector = N0.getNode();
         // Check that the type of EXTRACT_VECTOR_ELT matches the type of
         // BUILD_VECTOR.
         if (VT.getVectorElementType() !=

llvm/test/CodeGen/AArch64/build-vector-to-extract-subvec-crash.ll

+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc < %s -mtriple=aarch64-- | FileCheck %s
+
+target datalayout = "e-m:o-i64:64-i128:128-n32:64-S128"
+target triple = "arm64-apple-darwin"
+
+define i32 @widget(i64 %arg, <8 x i16> %arg1) {
+; CHECK-LABEL: widget:
+; CHECK:       // %bb.0: // %bb
+; CHECK-NEXT:    sub sp, sp, #16
+; CHECK-NEXT:    .cfi_def_cfa_offset 16
+; CHECK-NEXT:    umov w9, v0.h[0]
+; CHECK-NEXT:    mov x10, sp
+; CHECK-NEXT:    movi v0.2d, #0000000000000000
+; CHECK-NEXT:    bfi x10, x0, #1, #3
+; CHECK-NEXT:    mov x8, x0
+; CHECK-NEXT:    mov w0, wzr
+; CHECK-NEXT:    dup v1.8h, w9
+; CHECK-NEXT:    str q0, [sp]
+; CHECK-NEXT:    ld1 { v1.h }[1], [x10]
+; CHECK-NEXT:    str q1, [x8]
+; CHECK-NEXT:    add sp, sp, #16
+; CHECK-NEXT:    ret
+bb:
+  %inst = inttoptr i64 %arg to ptr
+  %inst2 = extractelement <8 x i16> %arg1, i64 0
+  store i16 %inst2, ptr %inst, align 2
+  %inst3 = getelementptr i16, ptr %inst, i64 1
+  %inst4 = getelementptr i16, ptr %inst, i64 2
+  %inst5 = extractelement <8 x i16> %arg1, i64 0
+  %inst6 = getelementptr i16, ptr %inst, i64 3
+  %inst7 = extractelement <8 x i16> zeroinitializer, i64 %arg
+  store i16 %inst7, ptr %inst3, align 2
+  %inst8 = extractelement <8 x i16> %arg1, i64 0
+  store i16 %inst8, ptr %inst4, align 2
+  store i16 %inst5, ptr %inst6, align 2
+  %inst9 = extractelement <8 x i16> %arg1, i64 0
+  %inst10 = getelementptr i16, ptr %inst, i64 4
+  store i16 %inst9, ptr %inst10, align 2
+  %inst11 = extractelement <8 x i16> %arg1, i64 0
+  %inst12 = getelementptr i16, ptr %inst, i64 5
+  store i16 %inst11, ptr %inst12, align 2
+  %inst13 = extractelement <8 x i16> %arg1, i64 0
+  %inst14 = getelementptr i16, ptr %inst, i64 6
+  store i16 %inst13, ptr %inst14, align 2
+  %inst15 = extractelement <8 x i16> %arg1, i64 0
+  %inst16 = getelementptr i16, ptr %inst, i64 7
+  store i16 %inst15, ptr %inst16, align 2
+  ret i32 0
+}
+