Be more conservative when forming compact regions.

Apply twice the negative bias on transparent blocks when computing the
compact regions. This excludes loop backedges from the region when only
one of the loop blocks uses the register.

Previously, we would include the backedge in the region if the loop
preheader and the loop latch both used the register, but the loop header
didn't.

When both the header and latch blocks use the register, we still keep it
live on the backedge.

llvm-svn: 136832

1 files changed, 2 insertions, 1 deletions

diff --git a/llvm/lib/CodeGen/SpillPlacement.h b/llvm/lib/CodeGen/SpillPlacement.h
index 9d1d676c54a..fc412f817cd 100644
--- a/llvm/lib/CodeGen/SpillPlacement.h
+++ b/llvm/lib/CodeGen/SpillPlacement.h
@@ -107,7 +107,8 @@ public:
   /// Entry = Exit = PrefSpill, and ChangesValue = false.
   ///
   /// @param Blocks Array of block numbers that prefer to spill in and out.
-  void addPrefSpill(ArrayRef<unsigned> Blocks);
+  /// @param Strong When true, double the negative bias for these blocks.
+  void addPrefSpill(ArrayRef<unsigned> Blocks, bool Strong);
 
   /// addLinks - Add transparent blocks with the given numbers.
   void addLinks(ArrayRef<unsigned> Links);