[llvm-commits] [llvm] r141138 - /llvm/trunk/lib/CodeGen/RegisterCoalescer.cpp

[Jakob Stoklund Olesen]

Author: stoklund
Date: Tue Oct  4 19:01:46 2011
New Revision: 141138

URL: http://llvm.org/viewvc/llvm-project?rev=141138&view=rev
Log:
Also add <def,undef> flags when coalescing sub-registers.

RegisterCoalescer can create sub-register defs when it is joining a
register with a sub-register.  Add <undef> flags to these new
sub-register defs where appropriate.

Modified:
    llvm/trunk/lib/CodeGen/RegisterCoalescer.cpp

Modified: llvm/trunk/lib/CodeGen/RegisterCoalescer.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/RegisterCoalescer.cpp?rev=141138&r1=141137&r2=141138&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/RegisterCoalescer.cpp (original)
+++ llvm/trunk/lib/CodeGen/RegisterCoalescer.cpp Tue Oct  4 19:01:46 2011
@@ -967,6 +967,14 @@
       Kills |= MO.isKill();
       Deads |= MO.isDead();
 
+      // Make sure we don't create read-modify-write defs accidentally.  We
+      // assume here that a SrcReg def cannot be joined into a live DstReg.  If
+      // RegisterCoalescer starts tracking partially live registers, we will
+      // need to check the actual LiveInterval to determine if DstReg is live
+      // here.
+      if (SubIdx && !Reads)
+        MO.setIsUndef();
+
       if (DstIsPhys)
         MO.substPhysReg(DstReg, *TRI);
       else