Reapply r185393.

Original commit message:

Remove floating point computations from SpillPlacement.cpp.

Patch by Benjamin Kramer!

Use the BlockFrequency class instead of floats in the Hopfield network
computations. This rescales the node Bias field from a [-2;2] float
range to two block frequencies BiasN and BiasP pulling in opposite
directions. This construct has a more predictable behavior when block
frequencies saturate.

The per-node scaling factors are no longer necessary, assuming the block
frequencies around a bundle are consistent.

This patch can cause the register allocator to make different spilling
decisions. The differences should be small.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@186434 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 5 insertions, 2 deletions

diff --git a/lib/CodeGen/SpillPlacement.h b/lib/CodeGen/SpillPlacement.h
index fc412f817c..a0480d587d 100644
--- a/lib/CodeGen/SpillPlacement.h
+++ b/lib/CodeGen/SpillPlacement.h
@@ -30,6 +30,7 @@
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/CodeGen/MachineFunctionPass.h"
+#include "llvm/Support/BlockFrequency.h"
 
 namespace llvm {
 
@@ -57,7 +58,7 @@ class SpillPlacement  : public MachineFunctionPass {
   SmallVector<unsigned, 8> RecentPositive;
 
   // Block frequencies are computed once. Indexed by block number.
-  SmallVector<float, 4> BlockFrequency;
+  SmallVector<BlockFrequency, 4> BlockFrequencies;
 
 public:
   static char ID; // Pass identification, replacement for typeid.
@@ -140,7 +141,9 @@ public:
   /// getBlockFrequency - Return the estimated block execution frequency per
   /// function invocation.
   float getBlockFrequency(unsigned Number) const {
-    return BlockFrequency[Number];
+    // FIXME: Return the BlockFrequency directly.
+    const float Scale = 1.0f / BlockFrequency::getEntryFrequency();
+    return BlockFrequencies[Number].getFrequency() * Scale;
   }
 
 private: