Break the spill placement algorithm into three parts: prepare, addConstraints, and finish.

This will allow us to abort the algorithm early if it is determined to be futile.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@129020 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 22 insertions, 15 deletions

diff --git a/lib/CodeGen/SpillPlacement.h b/lib/CodeGen/SpillPlacement.h
index b0135cbc36..d1c6ceb785 100644
--- a/lib/CodeGen/SpillPlacement.h
+++ b/lib/CodeGen/SpillPlacement.h
@@ -10,8 +10,8 @@
 // This analysis computes the optimal spill code placement between basic blocks.
 //
 // The runOnMachineFunction() method only precomputes some profiling information
-// about the CFG. The real work is done by placeSpills() which is called by the
-// register allocator.
+// about the CFG. The real work is done by prepare(), addConstraints(), and
+// finish() which are called by the register allocator.
 //
 // Given a variable that is live across multiple basic blocks, and given
 // constraints on the basic blocks where the variable is live, determine which
@@ -27,6 +27,7 @@
 #ifndef LLVM_CODEGEN_SPILLPLACEMENT_H
 #define LLVM_CODEGEN_SPILLPLACEMENT_H
 
+#include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/CodeGen/MachineFunctionPass.h"
 
@@ -44,7 +45,7 @@ class SpillPlacement  : public MachineFunctionPass {
   const MachineLoopInfo *loops;
   Node *nodes;
 
-  // Nodes that are active in the current computation. Owned by the placeSpills
+  // Nodes that are active in the current computation. Owned by the prepare()
   // caller.
   BitVector *ActiveNodes;
 
@@ -73,24 +74,31 @@ public:
     BorderConstraint Exit : 8;  ///< Constraint on block exit.
   };
 
-  /// placeSpills - Compute the optimal spill code placement given the
-  /// constraints. No MustSpill constraints will be violated, and the smallest
-  /// possible number of PrefX constraints will be violated, weighted by
-  /// expected execution frequencies.
-  /// @param LiveBlocks Constraints for blocks that have the variable live in or
-  ///                   live out. DontCare/DontCare means the variable is live
-  ///                   through the block. DontCare/X means the variable is live
-  ///                   out, but not live in.
+  /// prepare - Reset state and prepare for a new spill placement computation.
   /// @param RegBundles Bit vector to receive the edge bundles where the
   ///                   variable should be kept in a register. Each bit
   ///                   corresponds to an edge bundle, a set bit means the
   ///                   variable should be kept in a register through the
   ///                   bundle. A clear bit means the variable should be
-  ///                   spilled.
+  ///                   spilled. This vector is retained.
+  void prepare(BitVector &RegBundles);
+
+  /// addConstraints - Add constraints and biases. This method may be called
+  /// more than once to accumulate constraints.
+  /// @param LiveBlocks Constraints for blocks that have the variable live in or
+  ///                   live out. DontCare/DontCare means the variable is live
+  ///                   through the block. DontCare/X means the variable is live
+  ///                   out, but not live in.
+  void addConstraints(ArrayRef<BlockConstraint> LiveBlocks);
+
+  /// finish - Compute the optimal spill code placement given the
+  /// constraints. No MustSpill constraints will be violated, and the smallest
+  /// possible number of PrefX constraints will be violated, weighted by
+  /// expected execution frequencies.
+  /// The selected bundles are returned in the bitvector passed to prepare().
   /// @return True if a perfect solution was found, allowing the variable to be
   ///         in a register through all relevant bundles.
-  bool placeSpills(const SmallVectorImpl<BlockConstraint> &LiveBlocks,
-                   BitVector &RegBundles);
+  bool finish();
 
   /// getBlockFrequency - Return the estimated block execution frequency per
   /// function invocation.
@@ -104,7 +112,6 @@ private:
   virtual void releaseMemory();
 
   void activate(unsigned);
-  void prepareNodes(const SmallVectorImpl<BlockConstraint>&);
   void iterate(const SmallVectorImpl<unsigned>&);
 };