From 6b96623dcb0cdb092eccf27b4d0fff25ed28f4b5 Mon Sep 17 00:00:00 2001
From: Dominik Montada <dominik.montada@hightec-rt.com>
Date: Thu, 12 Mar 2020 09:03:08 +0100
Subject: [PATCH] [GlobalISel] fix crash in narrowScalarExtract if DstRegs only
 has one register

Summary: When narrowing a scalar G_EXTRACT where the destination lines up perfectly with a single result of the emitted G_UNMERGE_VALUES a COPY should be emitted instead of unconditionally trying to emit a G_MERGE_VALUES.

Reviewers: arsenm, dsanders

Reviewed By: arsenm

Subscribers: wdng, rovka, hiraditya, volkan, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D75743
---
 .../CodeGen/GlobalISel/LegalizerHelper.cpp    |  6 ++-
 .../GlobalISel/LegalizerHelperTest.cpp        | 39 +++++++++++++++++++
 2 files changed, 43 insertions(+), 2 deletions(-)

diff --git a/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp b/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
index 6384cc9dc44f..d0a51ed03f00 100644
--- a/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
@@ -3703,10 +3703,12 @@ LegalizerHelper::narrowScalarExtract(MachineInstr &MI, unsigned TypeIdx,
   }
 
   Register DstReg = MI.getOperand(0).getReg();
-  if(MRI.getType(DstReg).isVector())
+  if (MRI.getType(DstReg).isVector())
     MIRBuilder.buildBuildVector(DstReg, DstRegs);
-  else
+  else if (DstRegs.size() > 1)
     MIRBuilder.buildMerge(DstReg, DstRegs);
+  else
+    MIRBuilder.buildCopy(DstReg, DstRegs[0]);
   MI.eraseFromParent();
   return Legalized;
 }
diff --git a/llvm/unittests/CodeGen/GlobalISel/LegalizerHelperTest.cpp b/llvm/unittests/CodeGen/GlobalISel/LegalizerHelperTest.cpp
index 130db7289dd6..d359ab203a78 100644
--- a/llvm/unittests/CodeGen/GlobalISel/LegalizerHelperTest.cpp
+++ b/llvm/unittests/CodeGen/GlobalISel/LegalizerHelperTest.cpp
@@ -2302,4 +2302,43 @@ TEST_F(GISelMITest, LibcallFNearbyInt) {
   // Check
   EXPECT_TRUE(CheckMachineFunction(*MF, CheckStr)) << *MF;
 }
+
+TEST_F(GISelMITest, NarrowScalarExtract) {
+  setUp();
+  if (!TM)
+    return;
+
+  // Declare your legalization info
+  DefineLegalizerInfo(A, {
+    getActionDefinitionsBuilder(G_UNMERGE_VALUES).legalFor({{s32, s64}});
+    getActionDefinitionsBuilder(G_EXTRACT).legalFor({{s16, s32}});
+  });
+
+  LLT S16{LLT::scalar(16)};
+  LLT S32{LLT::scalar(32)};
+
+  auto MIBExtractS32 = B.buildExtract(S32, Copies[1], 32);
+  auto MIBExtractS16 = B.buildExtract(S16, Copies[1], 0);
+
+  AInfo Info(MF->getSubtarget());
+  DummyGISelObserver Observer;
+  LegalizerHelper Helper(*MF, Info, Observer, B);
+
+  EXPECT_EQ(LegalizerHelper::LegalizeResult::Legalized,
+            Helper.narrowScalar(*MIBExtractS32, 1, S32));
+
+  EXPECT_EQ(LegalizerHelper::LegalizeResult::Legalized,
+            Helper.narrowScalar(*MIBExtractS16, 1, S32));
+
+  const auto *CheckStr = R"(
+  CHECK: [[UV:%[0-9]+]]:_(s32), [[UV1:%[0-9]+]]:_(s32) = G_UNMERGE_VALUES
+  CHECK: [[COPY:%[0-9]+]]:_(s32) = COPY [[UV1]]
+  CHECK: [[UV3:%[0-9]+]]:_(s32), [[UV4:%[0-9]+]]:_(s32) = G_UNMERGE_VALUES
+  CHECK: [[EXTR:%[0-9]+]]:_(s16) = G_EXTRACT [[UV3]]:_(s32), 0
+  CHECK: [[COPY:%[0-9]+]]:_(s16) = COPY [[EXTR]]
+  )";
+
+  // Check
+  EXPECT_TRUE(CheckMachineFunction(*MF, CheckStr)) << *MF;
+}
 } // namespace