[llvm-branch-commits] [llvm] release/18.x: [GlobalISel] Fix fewerElementsVectorPhi to insert after G_PHIs (#87927) (PR #89240)

[via llvm-branch-commits]

https://github.com/AtariDreams created https://github.com/llvm/llvm-project/pull/89240

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.

(cherry picked from commit 2347020e4ce62ee7c7378824dc6ad2b94917a638)

>From 4b4805660e187ed58263e0e14038635d3303f074 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?D=C3=A1vid=20Ferenc=20Szab=C3=B3?=
 <30732159+dfszabo at users.noreply.github.com>
Date: Mon, 15 Apr 2024 11:01:55 +0200
Subject: [PATCH] [GlobalISel] Fix fewerElementsVectorPhi to insert after
 G_PHIs (#87927)

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.

(cherry picked from commit 2347020e4ce62ee7c7378824dc6ad2b94917a638)
---
 llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp           | 4 ++++
 llvm/unittests/CodeGen/GlobalISel/LegalizerHelperTest.cpp | 6 +++---
 2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp b/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
index c0c22e36004f72..47d045ac48171e 100644
--- a/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
@@ -4180,6 +4180,10 @@ 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 d7876b7ce87490..531360a697039c 100644
--- a/llvm/unittests/CodeGen/GlobalISel/LegalizerHelperTest.cpp
+++ b/llvm/unittests/CodeGen/GlobalISel/LegalizerHelperTest.cpp
@@ -1556,12 +1556,12 @@ 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: [[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: [[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: [[USE_OP:%[0-9]+]]:_(<5 x s32>) = G_AND [[BV]]:_, [[BV]]:_
   )";