[llvm] [GlobalISel] Fix fewerElementsVectorPhi to insert after G_PHIs (PR #87927)

[Dávid Ferenc Szabó via llvm-commits]

https://github.com/dfszabo updated https://github.com/llvm/llvm-project/pull/87927

>From 642785e66d5f4436748dfc8f5c03cb357e024102 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?D=C3=A1vid=20Ferenc=20Szab=C3=B3?=
 <szabodavidferenc at gmail.com>
Date: Sun, 7 Apr 2024 17:59:17 +0200
Subject: [PATCH] [GlobalISel] Fix fewerElementsVectorPhi to insert after
 G_PHIs

Currently the inserted mergelike instructions will be inserted at the location of the G_PHI. Seems like the behaviour was correct before, but the rework done in https://reviews.llvm.org/D114198 forgot to include the part which makes sure the instructions will be inserted after all the G_PHIs.
---
 llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp           | 4 ++++
 llvm/unittests/CodeGen/GlobalISel/LegalizerHelperTest.cpp | 4 +---
 2 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp b/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
index 95c6a359e52ec6..9412fa85cd3856 100644
--- a/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
@@ -4265,6 +4265,10 @@ LegalizerHelper::fewerElementsVectorPhi(GenericMachineInstr &MI,
     }
   }
 
+  // Set the insert point after the existing PHIs
+  MachineBasicBlock &MBB = *MI.getParent();
+  MIRBuilder.setInsertPt(MBB, MBB.getFirstNonPHI());
+
   // Merge small outputs into MI's def.
   if (NumLeftovers) {
     mergeMixedSubvectors(MI.getReg(0), OutputRegs);
diff --git a/llvm/unittests/CodeGen/GlobalISel/LegalizerHelperTest.cpp b/llvm/unittests/CodeGen/GlobalISel/LegalizerHelperTest.cpp
index 33155d2c9a9642..fd1bfc3e63a39d 100644
--- a/llvm/unittests/CodeGen/GlobalISel/LegalizerHelperTest.cpp
+++ b/llvm/unittests/CodeGen/GlobalISel/LegalizerHelperTest.cpp
@@ -1556,12 +1556,10 @@ TEST_F(AArch64GISelMITest, FewerElementsPhi) {
   CHECK: [[PHI0:%[0-9]+]]:_(<2 x s32>) = G_PHI [[INITVAL_E01]]:_(<2 x s32>), %bb.0, [[MIDVAL_E01]]:_(<2 x s32>), %bb.1
   CHECK: [[PHI1:%[0-9]+]]:_(<2 x s32>) = G_PHI [[INITVAL_E23]]:_(<2 x s32>), %bb.0, [[MIDVAL_E23]]:_(<2 x s32>), %bb.1
   CHECK: [[PHI2:%[0-9]+]]:_(s32) = G_PHI [[INITVAL_E4]]:_(s32), %bb.0, [[MIDVAL_E4]]:_(s32), %bb.1
+  CHECK: [[OTHER_PHI:%[0-9]+]]:_(s64) = G_PHI
   CHECK: [[UNMERGE0:%[0-9]+]]:_(s32), [[UNMERGE1:%[0-9]+]]:_(s32) = G_UNMERGE_VALUES [[PHI0]]:_(<2 x s32>)
   CHECK: [[UNMERGE2:%[0-9]+]]:_(s32), [[UNMERGE3:%[0-9]+]]:_(s32) = G_UNMERGE_VALUES [[PHI1]]:_(<2 x s32>)
   CHECK: [[BV:%[0-9]+]]:_(<5 x s32>) = G_BUILD_VECTOR [[UNMERGE0]]:_(s32), [[UNMERGE1]]:_(s32), [[UNMERGE2]]:_(s32), [[UNMERGE3]]:_(s32), [[PHI2]]:_(s32)
-
-  CHECK: [[OTHER_PHI:%[0-9]+]]:_(s64) = G_PHI
-
   CHECK: [[USE_OP:%[0-9]+]]:_(<5 x s32>) = G_AND [[BV]]:_, [[BV]]:_
   )";