[llvm] [ARM] Fix phi operand order issue in MVEGatherScatterLowering (PR #78208)

[David Green via llvm-commits]

https://github.com/davemgreen created https://github.com/llvm/llvm-project/pull/78208

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.

>From f947867d7db99986e6bd2438e74ae929946660cb Mon Sep 17 00:00:00 2001
From: David Green <david.green at arm.com>
Date: Mon, 15 Jan 2024 20:00:46 +0000
Subject: [PATCH] [ARM] Fix phi operand order issue in MVEGatherScatterLowering

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.
---
 llvm/lib/Target/ARM/MVEGatherScatterLowering.cpp         | 4 ++--
 llvm/test/CodeGen/Thumb2/mve-gather-optimisation-deep.ll | 6 +++---
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/llvm/lib/Target/ARM/MVEGatherScatterLowering.cpp b/llvm/lib/Target/ARM/MVEGatherScatterLowering.cpp
index 48e63e04b1197e7..bcfedd3414253ed 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 d14f2ddf325600d..cdfd2c845b55ab4 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