[ARM] Fix phi operand order issue in MVEGatherScatterLowering

[davemgreen]

With commuted operands on the phi node, the two old incoming values could be removed in the wrong order, removing newly added operand instead of the old one.

[llvmbot]

@llvm/pr-subscribers-backend-arm

Author: David Green (davemgreen)

Changes

With commuted operands on the phi node, the two old incoming values could be removed in the wrong order, removing newly added operand instead of the old one.

---

Full diff: https://github.com/llvm/llvm-project/pull/78208.diff

2 Files Affected:

• (modified) llvm/lib/Target/ARM/MVEGatherScatterLowering.cpp (+2-2)
• (modified) llvm/test/CodeGen/Thumb2/mve-gather-optimisation-deep.ll (+3-3)

diff --git a/llvm/lib/Target/ARM/MVEGatherScatterLowering.cpp b/llvm/lib/Target/ARM/MVEGatherScatterLowering.cpp
index 48e63e04b1197e..bcfedd3414253e 100644
--- a/llvm/lib/Target/ARM/MVEGatherScatterLowering.cpp
+++ b/llvm/lib/Target/ARM/MVEGatherScatterLowering.cpp
@@ -898,8 +898,8 @@ void MVEGatherScatterLowering::pushOutAdd(PHINode *&Phi,
   Phi->addIncoming(NewIndex, Phi->getIncomingBlock(StartIndex));
   Phi->addIncoming(Phi->getIncomingValue(IncrementIndex),
                    Phi->getIncomingBlock(IncrementIndex));
-  Phi->removeIncomingValue(IncrementIndex);
-  Phi->removeIncomingValue(StartIndex);
+  Phi->removeIncomingValue(1);
+  Phi->removeIncomingValue((unsigned)0);
 }
 
 void MVEGatherScatterLowering::pushOutMulShl(unsigned Opcode, PHINode *&Phi,
diff --git a/llvm/test/CodeGen/Thumb2/mve-gather-optimisation-deep.ll b/llvm/test/CodeGen/Thumb2/mve-gather-optimisation-deep.ll
index d14f2ddf325600..cdfd2c845b55ab 100644
--- a/llvm/test/CodeGen/Thumb2/mve-gather-optimisation-deep.ll
+++ b/llvm/test/CodeGen/Thumb2/mve-gather-optimisation-deep.ll
@@ -62,11 +62,11 @@ end:
   ret void;
 }
 
-define arm_aapcs_vfpcc void @push_out_add_sub_block_c(i32* noalias nocapture readonly %data, i32* noalias nocapture %dst, i32 %n.vec) {
-; CHECK-LABEL: @push_out_add_sub_block_c(
+define arm_aapcs_vfpcc void @push_out_add_sub_block_commutedphi(i32* noalias nocapture readonly %data, i32* noalias nocapture %dst, i32 %n.vec) {
+; CHECK-LABEL: @push_out_add_sub_block_commutedphi(
 ; CHECK-NEXT:  vector.ph:
 ; CHECK-NEXT:    [[PUSHEDOUTADD:%.*]] = add <4 x i32> <i32 0, i32 2, i32 4, i32 6>, <i32 6, i32 6, i32 6, i32 6>
-; CHECK-NEXT:    [[SCALEDINDEX:%.*]] = shl <4 x i32> <i32 0, i32 2, i32 4, i32 6>, <i32 2, i32 2, i32 2, i32 2>
+; CHECK-NEXT:    [[SCALEDINDEX:%.*]] = shl <4 x i32> [[PUSHEDOUTADD]], <i32 2, i32 2, i32 2, i32 2>
 ; CHECK-NEXT:    [[TMP0:%.*]] = ptrtoint ptr [[DATA:%.*]] to i32
 ; CHECK-NEXT:    [[DOTSPLATINSERT:%.*]] = insertelement <4 x i32> poison, i32 [[TMP0]], i64 0
 ; CHECK-NEXT:    [[DOTSPLAT:%.*]] = shufflevector <4 x i32> [[DOTSPLATINSERT]], <4 x i32> poison, <4 x i32> zeroinitializer

[ostannard]

LGTM

[davemgreen]

Thanks