[llvm] r225416 - RegisterCoalescer: Do not remove IMPLICIT_DEFS if they are required for subranges.

[Matthias Braun]

Author: matze
Date: Wed Jan  7 18:21:23 2015
New Revision: 225416

URL: http://llvm.org/viewvc/llvm-project?rev=225416&view=rev
Log:
RegisterCoalescer: Do not remove IMPLICIT_DEFS if they are required for subranges.

The register coalescer used to remove implicit_defs when they are
covered by the main range anyway. With subreg liveness tracking we can't
do that anymore in places where the IMPLICIT_DEF is required as begin of
a subregister liverange.

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=225416&r1=225415&r2=225416&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/RegisterCoalescer.cpp (original)
+++ llvm/trunk/lib/CodeGen/RegisterCoalescer.cpp Wed Jan  7 18:21:23 2015
@@ -1912,8 +1912,14 @@ JoinVals::analyzeValue(unsigned ValNo, J
     return CR_Replace;
 
   // Check for simple erasable conflicts.
-  if (DefMI->isImplicitDef())
+  if (DefMI->isImplicitDef()) {
+    // We need the def for the subregister if there is nothing else live at the
+    // subrange at this point.
+    if (TrackSubRegLiveness
+        && (V.WriteLanes & (OtherV.ValidLanes | OtherV.WriteLanes)) == 0)
+      return CR_Replace;
     return CR_Erase;
+  }
 
   // Include the non-conflict where DefMI is a coalescable copy that kills
   // OtherVNI. We still want the copy erased and value numbers merged.