Revert to RA_Assign when a virtreg separates into components.

When dead code elimination deletes a PHI value, the virtual register may
split into multiple connected components. In that case, revert each
component to the RS_Assign stage.

The new components are guaranteed to be smaller (the original value
numbers are distributed among the components), so this will always be
making progress. The components are now allowed to evict other live
ranges or be split again.

llvm-svn: 136034

1 files changed, 3 insertions, 1 deletions

diff --git a/llvm/lib/CodeGen/RegAllocGreedy.cpp b/llvm/lib/CodeGen/RegAllocGreedy.cpp
index 147e8035340..d0b40dd113d 100644
--- a/llvm/lib/CodeGen/RegAllocGreedy.cpp
+++ b/llvm/lib/CodeGen/RegAllocGreedy.cpp
@@ -341,8 +341,10 @@ void RAGreedy::LRE_WillShrinkVirtReg(unsigned VirtReg) {
 
 void RAGreedy::LRE_DidCloneVirtReg(unsigned New, unsigned Old) {
   // LRE may clone a virtual register because dead code elimination causes it to
-  // be split into connected components. Ensure that the new register gets the
+  // be split into connected components. The new components are much smaller
+  // than the original, so they should get a new chance at being assigned.
   // same stage as the parent.
+  ExtraRegInfo[Old].Stage = RS_Assign;
   ExtraRegInfo.grow(New);
   ExtraRegInfo[New] = ExtraRegInfo[Old];
 }