Split around single instructions to enable register class inflation.

Normally, we don't create a live range for a single instruction in a
basic block, the spiller does that anyway. However, when splitting a
live range that belongs to a proper register sub-class, inserting these
extra COPY instructions completely remove the constraints from the
remainder interval, and it may be allocated from the larger super-class.

The spiller will mop up these small live ranges if we end up spilling
anyway. It calls them snippets.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@136989 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 10 insertions, 0 deletions

diff --git a/lib/CodeGen/SplitKit.h b/lib/CodeGen/SplitKit.h
index 33c3c07eb4..8bed2a0fb6 100644
--- a/lib/CodeGen/SplitKit.h
+++ b/lib/CodeGen/SplitKit.h
@@ -185,6 +185,16 @@ public:
 
   typedef SmallPtrSet<const MachineBasicBlock*, 16> BlockPtrSet;
 
+  /// shouldSplitSingleBlock - Returns true if it would help to create a local
+  /// live range for the instructions in BI. There is normally no benefit to
+  /// creating a live range for a single instruction, but it does enable
+  /// register class inflation if the instruction has a restricted register
+  /// class.
+  ///
+  /// @param BI           The block to be isolated.
+  /// @param SingleInstrs True when single instructions should be isolated.
+  bool shouldSplitSingleBlock(const BlockInfo &BI, bool SingleInstrs) const;
+
   /// getMultiUseBlocks - Add basic blocks to Blocks that may benefit from
   /// having CurLI split to a new live interval. Return true if Blocks can be
   /// passed to SplitEditor::splitSingleBlocks.