From 3828242c7e6527aaacff32f0c42b0e0fd37a20a6 Mon Sep 17 00:00:00 2001
From: Alexander Timofeev <Alexander.Timofeev@amd.com>
Date: Mon, 16 Oct 2017 14:35:29 +0000
Subject: [PATCH] [AMDGPU] Prevent Machine Copy Propagation from replacing live
 copy with the dead one

Differential revision: https://reviews.llvm.org/D38754

llvm-svn: 315908
---
 llvm/lib/CodeGen/MachineCopyPropagation.cpp | 24 +++++++++---------
 llvm/test/CodeGen/AMDGPU/dead_copy.mir      | 27 +++++++++++++++++++++
 2 files changed, 40 insertions(+), 11 deletions(-)
 create mode 100644 llvm/test/CodeGen/AMDGPU/dead_copy.mir

diff --git a/llvm/lib/CodeGen/MachineCopyPropagation.cpp b/llvm/lib/CodeGen/MachineCopyPropagation.cpp
index 4655b5ba7044..030db4366e93 100644
--- a/llvm/lib/CodeGen/MachineCopyPropagation.cpp
+++ b/llvm/lib/CodeGen/MachineCopyPropagation.cpp
@@ -275,18 +275,20 @@ void MachineCopyPropagation::CopyPropagateBlock(MachineBasicBlock &MBB) {
         ClobberRegister(Reg);
       }
 
-      // Remember Def is defined by the copy.
-      for (MCSubRegIterator SR(Def, TRI, /*IncludeSelf=*/true); SR.isValid();
-           ++SR) {
-        CopyMap[*SR] = MI;
-        AvailCopyMap[*SR] = MI;
-      }
+      if (!MI->getOperand(0).isDead() && !MI->getOperand(1).isUndef()) {
+        // Remember Def is defined by the copy.
+        for (MCSubRegIterator SR(Def, TRI, /*IncludeSelf=*/true); SR.isValid();
+             ++SR) {
+          CopyMap[*SR] = MI;
+          AvailCopyMap[*SR] = MI;
+        }
 
-      // Remember source that's copied to Def. Once it's clobbered, then
-      // it's no longer available for copy propagation.
-      RegList &DestList = SrcMap[Src];
-      if (!is_contained(DestList, Def))
-        DestList.push_back(Def);
+        // Remember source that's copied to Def. Once it's clobbered, then
+        // it's no longer available for copy propagation.
+        RegList &DestList = SrcMap[Src];
+        if (!is_contained(DestList, Def))
+          DestList.push_back(Def);
+      }
 
       continue;
     }
diff --git a/llvm/test/CodeGen/AMDGPU/dead_copy.mir b/llvm/test/CodeGen/AMDGPU/dead_copy.mir
new file mode 100644
index 000000000000..76a25f2ba808
--- /dev/null
+++ b/llvm/test/CodeGen/AMDGPU/dead_copy.mir
@@ -0,0 +1,27 @@
+# RUN: llc -o - %s -march=amdgcn -mcpu=fiji  -run-pass=machine-cp -verify-machineinstrs | FileCheck -check-prefix=GCN %s
+
+# GCN-LABEL: dead_copy
+# GCN:       bb.0
+# GCN-NOT:   dead %vgpr5 = COPY undef %vgpr11, implicit %exec
+# GCN:       %vgpr5 = COPY %vgpr11, implicit %exec
+
+---
+name: dead_copy
+
+body:    |
+
+  bb.0:
+    liveins: %vgpr11, %sgpr0, %sgpr1, %vgpr6, %vgpr7, %vgpr4
+    
+    dead %vgpr5 = COPY undef %vgpr11, implicit %exec
+    
+    %vgpr5 = COPY %vgpr11, implicit %exec
+    
+    %sgpr14 = S_ADD_U32 %sgpr0, target-flags(amdgpu-gotprel) 1136, implicit-def %scc
+    %sgpr15 = S_ADDC_U32 %sgpr1, target-flags(amdgpu-gotprel32-lo) 0, implicit-def dead %scc, implicit %scc
+    
+    %vgpr10 = COPY killed %sgpr14, implicit %exec
+    %vgpr11 = COPY killed %sgpr15, implicit %exec
+    
+    FLAT_STORE_DWORDX4 %vgpr10_vgpr11, %vgpr4_vgpr5_vgpr6_vgpr7, 0, 0, 0, implicit %exec, implicit %flat_scr
+...
-- 
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