From 57d315b7c18c4e56f6d20ff8f497e1e9c2ba1a9b Mon Sep 17 00:00:00 2001
From: Patrik Hagglund <patrik.h.hagglund@ericsson.com>
Date: Tue, 9 Sep 2014 07:47:00 +0000
Subject: [PATCH] [MachineSinking] Conservatively clear kill flags after
 coalescing.

This solves the problem of having a kill flag inside a loop
with a definition of the register prior to the loop:

%vreg368<def> ...

Inside loop:

        %vreg520<def> = COPY %vreg368
        %vreg568<def,tied1> = add %vreg341<tied0>, %vreg520<kill>

=> was coalesced into =>

        %vreg568<def,tied1> = add %vreg341<tied0>, %vreg368<kill>

MachineVerifier then complained:
*** Bad machine code: Virtual register killed in block, but needed live out. ***

The kill flag for %vreg368 is incorrect, and is cleared by this patch.

This is similar to the clearing done at the end of
MachineSinking::SinkInstruction().

Patch provided by Jonas Paulsson.

Reviewed by Quentin Colombet and Juergen Ributzka.

llvm-svn: 217427
---
 llvm/lib/CodeGen/MachineSink.cpp | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/llvm/lib/CodeGen/MachineSink.cpp b/llvm/lib/CodeGen/MachineSink.cpp
index 77820010cef0..261af546d726 100644
--- a/llvm/lib/CodeGen/MachineSink.cpp
+++ b/llvm/lib/CodeGen/MachineSink.cpp
@@ -157,6 +157,11 @@ bool MachineSinking::PerformTrivialForwardCoalescing(MachineInstr *MI,
   DEBUG(dbgs() << "*** to: " << *MI);
   MRI->replaceRegWith(DstReg, SrcReg);
   MI->eraseFromParent();
+
+  // Conservatively, clear any kill flags, since it's possible that they are no
+  // longer correct.
+  MRI->clearKillFlags(SrcReg);
+
   ++NumCoalesces;
   return true;
 }