[llvm] r302877 - Handle a COPY with undef source operand in LowerCopy()

[Jonas Paulsson via llvm-commits]

Author: jonpa
Date: Fri May 12 01:32:03 2017
New Revision: 302877

URL: http://llvm.org/viewvc/llvm-project?rev=302877&view=rev
Log:
Handle a COPY with undef source operand in LowerCopy()

Llvm-stress discovered that a COPY may end up in ExpandPostRA::LowerCopy()
with an undef source operand. It is not possible for the target to handle
this, as this flag is not passed to TII->copyPhysReg().

This patch solves this by treating such a COPY as an identity COPY.

Review: Matthias Braun
https://reviews.llvm.org/D32892

Added:
    llvm/trunk/test/CodeGen/SystemZ/lower-copy-undef-src.mir
Modified:
    llvm/trunk/lib/CodeGen/ExpandPostRAPseudos.cpp

Modified: llvm/trunk/lib/CodeGen/ExpandPostRAPseudos.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/ExpandPostRAPseudos.cpp?rev=302877&r1=302876&r2=302877&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/ExpandPostRAPseudos.cpp (original)
+++ llvm/trunk/lib/CodeGen/ExpandPostRAPseudos.cpp Fri May 12 01:32:03 2017
@@ -142,8 +142,9 @@ bool ExpandPostRA::LowerCopy(MachineInst
   MachineOperand &DstMO = MI->getOperand(0);
   MachineOperand &SrcMO = MI->getOperand(1);
 
-  if (SrcMO.getReg() == DstMO.getReg()) {
-    DEBUG(dbgs() << "identity copy: " << *MI);
+  bool IdentityCopy = (SrcMO.getReg() == DstMO.getReg());
+  if (IdentityCopy || SrcMO.isUndef()) {
+    DEBUG(dbgs() << (IdentityCopy ? "identity copy: " : "undef copy:    ") << *MI);
     // No need to insert an identity copy instruction, but replace with a KILL
     // if liveness is changed.
     if (SrcMO.isUndef() || MI->getNumOperands() > 2) {

Added: llvm/trunk/test/CodeGen/SystemZ/lower-copy-undef-src.mir
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/SystemZ/lower-copy-undef-src.mir?rev=302877&view=auto
==============================================================================
--- llvm/trunk/test/CodeGen/SystemZ/lower-copy-undef-src.mir (added)
+++ llvm/trunk/test/CodeGen/SystemZ/lower-copy-undef-src.mir Fri May 12 01:32:03 2017
@@ -0,0 +1,14 @@
+# RUN: llc -mtriple=s390x-linux-gnu -mcpu=z13 -run-pass=postrapseudos -o - %s | FileCheck %s
+#
+# Test that a COPY with an undef source operand gets handled like an identity
+# copy rather than lowered into a target instruction with the undef flag
+# dropped.
+---
+# CHECK-LABEL: name: undef_copy
+# CHECK: %r13d = KILL undef %r0d, implicit killed %r12q, implicit-def %r12q
+name: undef_copy
+tracksRegLiveness: true
+body: |
+  bb.0:
+    liveins: %r12q
+    %r13d = COPY undef %r0d, implicit killed %r12q, implicit-def %r12q