From 341473c86d19cad5f3be432533ecdb42d9e07044 Mon Sep 17 00:00:00 2001
From: Benjamin Kramer <benny.kra@googlemail.com>
Date: Sun, 23 Oct 2011 11:19:14 +0000
Subject: [PATCH] Add compare operators to BranchProbability and use it to
 determine if an edge is hot.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@142751 91177308-0d34-0410-b5e6-96231b3b80d8
---
 include/llvm/Support/BranchProbability.h | 18 ++++++++++++++++--
 lib/Analysis/BranchProbabilityInfo.cpp   | 12 ++++--------
 lib/Support/BranchProbability.cpp        |  7 -------
 unittests/Support/BlockFrequencyTest.cpp | 20 ++++++++++++++++++++
 4 files changed, 40 insertions(+), 17 deletions(-)

diff --git a/include/llvm/Support/BranchProbability.h b/include/llvm/Support/BranchProbability.h
index 05c24d4fcfc..a1e5ceb6255 100644
--- a/include/llvm/Support/BranchProbability.h
+++ b/include/llvm/Support/BranchProbability.h
@@ -15,6 +15,7 @@
 #define LLVM_SUPPORT_BRANCHPROBABILITY_H
 
 #include "llvm/Support/DataTypes.h"
+#include <cassert>
 
 namespace llvm {
 
@@ -22,15 +23,21 @@ class raw_ostream;
 
 // This class represents Branch Probability as a non-negative fraction.
 class BranchProbability {
-
   // Numerator
   uint32_t N;
 
   // Denominator
   uint32_t D;
 
+  int64_t compare(BranchProbability RHS) const {
+    return (uint64_t)N * RHS.D - (uint64_t)D * RHS.N;
+  }
+
 public:
-  BranchProbability(uint32_t n, uint32_t d);
+  BranchProbability(uint32_t n, uint32_t d) : N(n), D(d) {
+    assert(d > 0 && "Denomiator cannot be 0!");
+    assert(n <= d && "Probability cannot be bigger than 1!");
+  }
 
   uint32_t getNumerator() const { return N; }
   uint32_t getDenominator() const { return D; }
@@ -43,6 +50,13 @@ public:
   void print(raw_ostream &OS) const;
 
   void dump() const;
+
+  bool operator==(BranchProbability RHS) const { return compare(RHS) == 0; }
+  bool operator!=(BranchProbability RHS) const { return compare(RHS) != 0; }
+  bool operator< (BranchProbability RHS) const { return compare(RHS) <  0; }
+  bool operator> (BranchProbability RHS) const { return compare(RHS) >  0; }
+  bool operator<=(BranchProbability RHS) const { return compare(RHS) <= 0; }
+  bool operator>=(BranchProbability RHS) const { return compare(RHS) >= 0; }
 };
 
 raw_ostream &operator<<(raw_ostream &OS, const BranchProbability &Prob);
diff --git a/lib/Analysis/BranchProbabilityInfo.cpp b/lib/Analysis/BranchProbabilityInfo.cpp
index fc69da9e672..4f15858aa34 100644
--- a/lib/Analysis/BranchProbabilityInfo.cpp
+++ b/lib/Analysis/BranchProbabilityInfo.cpp
@@ -476,12 +476,8 @@ uint32_t BranchProbabilityInfo::getSumForBlock(const BasicBlock *BB) const {
 bool BranchProbabilityInfo::
 isEdgeHot(const BasicBlock *Src, const BasicBlock *Dst) const {
   // Hot probability is at least 4/5 = 80%
-  uint32_t Weight = getEdgeWeight(Src, Dst);
-  uint32_t Sum = getSumForBlock(Src);
-
-  // FIXME: Implement BranchProbability::compare then change this code to
-  // compare this BranchProbability against a static "hot" BranchProbability.
-  return (uint64_t)Weight * 5 > (uint64_t)Sum * 4;
+  // FIXME: Compare against a static "hot" BranchProbability.
+  return getEdgeProbability(Src, Dst) > BranchProbability(4, 5);
 }
 
 BasicBlock *BranchProbabilityInfo::getHotSucc(BasicBlock *BB) const {
@@ -503,8 +499,8 @@ BasicBlock *BranchProbabilityInfo::getHotSucc(BasicBlock *BB) const {
     }
   }
 
-  // FIXME: Use BranchProbability::compare.
-  if ((uint64_t)MaxWeight * 5 > (uint64_t)Sum * 4)
+  // Hot probability is at least 4/5 = 80%
+  if (BranchProbability(MaxWeight, Sum) > BranchProbability(4, 5))
     return MaxSucc;
 
   return 0;
diff --git a/lib/Support/BranchProbability.cpp b/lib/Support/BranchProbability.cpp
index 49d04ed8365..5a5e07583d9 100644
--- a/lib/Support/BranchProbability.cpp
+++ b/lib/Support/BranchProbability.cpp
@@ -17,13 +17,6 @@
 
 using namespace llvm;
 
-BranchProbability::BranchProbability(uint32_t n, uint32_t d) {
-  assert(d > 0 && "Denomiator cannot be 0!");
-  assert(n <= d && "Probability cannot be bigger than 1!");
-  N = n;
-  D = d;
-}
-
 void BranchProbability::print(raw_ostream &OS) const {
   OS << N << " / " << D << " = " << ((double)N / D);
 }
diff --git a/unittests/Support/BlockFrequencyTest.cpp b/unittests/Support/BlockFrequencyTest.cpp
index edeea9b357f..ac3cedf1869 100644
--- a/unittests/Support/BlockFrequencyTest.cpp
+++ b/unittests/Support/BlockFrequencyTest.cpp
@@ -53,4 +53,24 @@ TEST(BlockFrequencyTest, MaxToMax) {
   EXPECT_EQ(Freq.getFrequency(), UINT64_MAX);
 }
 
+TEST(BlockFrequencyTest, ProbabilityCompare) {
+  BranchProbability A(4, 5);
+  BranchProbability B(4U << 29, 5U << 29);
+  BranchProbability C(3, 4);
+
+  EXPECT_TRUE(A == B);
+  EXPECT_FALSE(A != B);
+  EXPECT_FALSE(A < B);
+  EXPECT_FALSE(A > B);
+  EXPECT_TRUE(A <= B);
+  EXPECT_TRUE(A >= B);
+
+  EXPECT_FALSE(B == C);
+  EXPECT_TRUE(B != C);
+  EXPECT_FALSE(B < C);
+  EXPECT_TRUE(B > C);
+  EXPECT_FALSE(B <= C);
+  EXPECT_TRUE(B >= C);
+}
+
 }