Introduce MachineBranchProbabilityInfo class, which has similar API to

BranchProbabilityInfo (expect setEdgeWeight which is not available here).
Branch Weights are kept in MachineBasicBlocks. To turn off this analysis
set -use-mbpi=false.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@133184 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 77 insertions, 0 deletions

diff --git a/include/llvm/CodeGen/MachineBranchProbabilityInfo.h b/include/llvm/CodeGen/MachineBranchProbabilityInfo.h
new file mode 100644
index 0000000000..f3b3e0e687
--- /dev/null
+++ b/include/llvm/CodeGen/MachineBranchProbabilityInfo.h
@@ -0,0 +1,77 @@
+
+//==- MachineBranchProbabilityInfo.h - Machine Branch Probability Analysis -==//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This pass is used to evaluate branch probabilties on machine basic blocks.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CODEGEN_MACHINEBRANCHPROBABILITYINFO_H
+#define LLVM_CODEGEN_MACHINEBRANCHPROBABILITYINFO_H
+
+#include "llvm/Pass.h"
+#include "llvm/Support/BranchProbability.h"
+#include <climits>
+
+namespace llvm {
+
+class raw_ostream;
+
+class MachineBranchProbabilityInfo : public ImmutablePass {
+
+  // Default weight value. Used when we don't have information about the edge.
+  // TODO: DEFAULT_WEIGHT makes sense during static predication, when none of
+  // the successors have a weight yet. But it doesn't make sense when providing
+  // weight to an edge that may have siblings with non-zero weights. This can
+  // be handled various ways, but it's probably fine for an edge with unknown
+  // weight to just "inherit" the non-zero weight of an adjacent successor.
+  static const uint32_t DEFAULT_WEIGHT = 16;
+
+  // Get sum of the block successors' weights.
+  uint32_t getSumForBlock(MachineBasicBlock *MBB) const;
+
+public:
+  static char ID;
+
+  MachineBranchProbabilityInfo() : ImmutablePass(ID) {
+    PassRegistry &Registry = *PassRegistry::getPassRegistry();
+    initializeMachineBranchProbabilityInfoPass(Registry);
+  }
+
+  void getAnalysisUsage(AnalysisUsage &AU) const {
+    AU.setPreservesAll();
+  }
+
+  // Return edge weight. If we don't have any informations about it - return
+  // DEFAULT_WEIGHT.
+  uint32_t getEdgeWeight(MachineBasicBlock *Src, MachineBasicBlock *Dst) const;
+
+  // A 'Hot' edge is an edge which probability is >= 80%.
+  bool isEdgeHot(MachineBasicBlock *Src, MachineBasicBlock *Dst) const;
+
+  // Return a hot successor for the block BB or null if there isn't one.
+  MachineBasicBlock *getHotSucc(MachineBasicBlock *MBB) const;
+
+  // Return a probability as a fraction between 0 (0% probability) and
+  // 1 (100% probability), however the value is never equal to 0, and can be 1
+  // only iff SRC block has only one successor.
+  BranchProbability getEdgeProbability(MachineBasicBlock *Src,
+                                       MachineBasicBlock *Dst) const;
+
+  // Print value between 0 (0% probability) and 1 (100% probability),
+  // however the value is never equal to 0, and can be 1 only iff SRC block
+  // has only one successor.
+  raw_ostream &printEdgeProbability(raw_ostream &OS, MachineBasicBlock *Src,
+                                    MachineBasicBlock *Dst) const;
+};
+
+}
+
+
+#endif