[AArch64] Fix legalization of i128 ctpop without neon

[nikic]

Summary

If neon is disabled, LowerCTPOP will return SDValue() to indicate that normal legalization will be used. However, ReplaceNodeResults does not check for this and pushes the empty SDValue() onto the result vector, which will subsequently result in a crash.

[dmgreen]

LGTM. Thanks.

llvm/lib/Target/AArch64/AArch64ISelLowering.cpp

void AArch64TargetLowering::ReplaceNodeResults(
   case ISD::VECREDUCE_SMAX:
   case ISD::VECREDUCE_SMIN:
   case ISD::VECREDUCE_UMAX:
   case ISD::VECREDUCE_UMIN:
     Results.push_back(LowerVECREDUCE(SDValue(N, 0), DAG));
     return;
 
   case ISD::CTPOP:
-    Results.push_back(LowerCTPOP(SDValue(N, 0), DAG));
+    if (SDValue Result = LowerCTPOP(SDValue(N, 0), DAG))
+      Results.push_back(Result);
     return;
   case AArch64ISD::SADDV:
     ReplaceReductionResults(N, Results, DAG, ISD::ADD, AArch64ISD::SADDV);
     return;
   case AArch64ISD::UADDV:
     ReplaceReductionResults(N, Results, DAG, ISD::ADD, AArch64ISD::UADDV);
     return;
   case AArch64ISD::SMINV:

llvm/test/CodeGen/AArch64/ctpop-nonean.ll

+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc -mtriple=aarch64-none-linux-gnu -mattr=-neon < %s | FileCheck %s
+
+declare i128 @llvm.ctpop.i128(i128)
+
+define i128 @ctpop_i128(i128 %i) {
+; CHECK-LABEL: ctpop_i128:
+; CHECK:       // %bb.0:
+; CHECK-NEXT:    lsr x8, x1, #1
+; CHECK-NEXT:    and x8, x8, #0x5555555555555555
+; CHECK-NEXT:    sub x8, x1, x8
+; CHECK-NEXT:    lsr x10, x0, #1
+; CHECK-NEXT:    and x10, x10, #0x5555555555555555
+; CHECK-NEXT:    and x11, x8, #0x3333333333333333
+; CHECK-NEXT:    lsr x8, x8, #2
+; CHECK-NEXT:    sub x10, x0, x10
+; CHECK-NEXT:    and x8, x8, #0x3333333333333333
+; CHECK-NEXT:    add x8, x11, x8
+; CHECK-NEXT:    and x11, x10, #0x3333333333333333
+; CHECK-NEXT:    lsr x10, x10, #2
+; CHECK-NEXT:    and x10, x10, #0x3333333333333333
+; CHECK-NEXT:    add x10, x11, x10
+; CHECK-NEXT:    add x8, x8, x8, lsr #4
+; CHECK-NEXT:    add x10, x10, x10, lsr #4
+; CHECK-NEXT:    mov x9, #72340172838076673
+; CHECK-NEXT:    and x8, x8, #0xf0f0f0f0f0f0f0f
+; CHECK-NEXT:    and x10, x10, #0xf0f0f0f0f0f0f0f
+; CHECK-NEXT:    mul x8, x8, x9
+; CHECK-NEXT:    mul x9, x10, x9
+; CHECK-NEXT:    lsr x9, x9, #56
+; CHECK-NEXT:    add x0, x9, x8, lsr #56
+; CHECK-NEXT:    mov x1, xzr
+; CHECK-NEXT:    ret
+  %c = call i128 @llvm.ctpop.i128(i128 %i)
+  ret i128 %c
+}