[BPI] Add multiplication by scalar operators to BranchProbability

[skatkov]

Summary

This patch just adds two operators to BranchProbability class:
(BP * scalar) and (BP *= scalar).

[skatkov]

This patch is actually reviewed as part of https://reviews.llvm.org/D32124

[chandlerc]

Yeah, still LGTM. =D Tiny nit pick though...

unittests/Support/BranchProbabilityTest.cpp

160

Call it 'Min' to fit with our naming convensions.

include/llvm/Support/BranchProbability.h

public:
 
   BranchProbability &operator*=(BranchProbability RHS) {
     assert(N != UnknownN && RHS.N != UnknownN &&
            "Unknown probability cannot participate in arithmetics.");
     N = (static_cast<uint64_t>(N) * RHS.N + D / 2) / D;
     return *this;
   }
 
+  BranchProbability &operator*=(uint32_t RHS) {
+    assert(N != UnknownN &&
+           "Unknown probability cannot participate in arithmetics.");
+    N = (uint64_t(N) * RHS > D) ? D : N * RHS;
+    return *this;
+  }
+
   BranchProbability &operator/=(uint32_t RHS) {
     assert(N != UnknownN &&
            "Unknown probability cannot participate in arithmetics.");
     assert(RHS > 0 && "The divider cannot be zero.");
     N /= RHS;
     return *this;
   }
 
   BranchProbability operator+(BranchProbability RHS) const {
     BranchProbability Prob(*this);
     return Prob += RHS;
   }
 
   BranchProbability operator-(BranchProbability RHS) const {
     BranchProbability Prob(*this);
     return Prob -= RHS;
   }
 
   BranchProbability operator*(BranchProbability RHS) const {
     BranchProbability Prob(*this);
     return Prob *= RHS;
   }
 
+  BranchProbability operator*(uint32_t RHS) const {
+    BranchProbability Prob(*this);
+    return Prob *= RHS;
+  }
+
   BranchProbability operator/(uint32_t RHS) const {
     BranchProbability Prob(*this);
     return Prob /= RHS;
   }
 
   bool operator==(BranchProbability RHS) const { return N == RHS.N; }
   bool operator!=(BranchProbability RHS) const { return !(*this == RHS); }
 

unittests/Support/BranchProbabilityTest.cpp

TEST(BranchProbabilityTest, MoreOperators) {
   EXPECT_FALSE(BigZero == BigOne);
   EXPECT_TRUE(BigZero != BigOne);
   EXPECT_TRUE(BigZero < BigOne);
   EXPECT_FALSE(BigZero > BigOne);
   EXPECT_TRUE(BigZero <= BigOne);
   EXPECT_FALSE(BigZero >= BigOne);
 }
 
+TEST(BranchProbabilityTest, ArithmeticOperators) {
+  BP Z(0, 1);
+  BP O(1, 1);
+  BP H(1, 2);
+  BP Q(1, 4);
+  BP Q3(3, 4);
+
+  EXPECT_EQ(Z + O, O);
+  EXPECT_EQ(H + Z, H);
+  EXPECT_EQ(H + H, O);
+  EXPECT_EQ(Q + H, Q3);
+  EXPECT_EQ(Q + Q3, O);
+  EXPECT_EQ(H + Q3, O);
+  EXPECT_EQ(Q3 + Q3, O);
+
+  EXPECT_EQ(Z - O, Z);
+  EXPECT_EQ(O - Z, O);
+  EXPECT_EQ(O - H, H);
+  EXPECT_EQ(O - Q, Q3);
+  EXPECT_EQ(Q3 - H, Q);
+  EXPECT_EQ(Q - H, Z);
+  EXPECT_EQ(Q - Q3, Z);
+
+  EXPECT_EQ(Z * O, Z);
+  EXPECT_EQ(H * H, Q);
+  EXPECT_EQ(Q * O, Q);
+  EXPECT_EQ(O * O, O);
+  EXPECT_EQ(Z * Z, Z);
+
+  EXPECT_EQ(Z * 3, Z);
+  EXPECT_EQ(Q * 3, Q3);
+  EXPECT_EQ(H * 3, O);
+  EXPECT_EQ(Q3 * 2, O);
+  EXPECT_EQ(O * UINT32_MAX, O);
+
+  EXPECT_EQ(Z / 4, Z);
+  EXPECT_EQ(O / 4, Q);
+  EXPECT_EQ(Q3 / 3, Q);
+  EXPECT_EQ(H / 2, Q);
+  EXPECT_EQ(O / 2, H);
+  EXPECT_EQ(H / UINT32_MAX, Z);
+
+  BP MIN(1, 1u << 31);
+
+  EXPECT_EQ(O / UINT32_MAX, Z);
+  EXPECT_EQ(MIN * UINT32_MAX, O);
+}
+
 TEST(BranchProbabilityTest, getCompl) {
   EXPECT_EQ(BP(5, 7), BP(2, 7).getCompl());
   EXPECT_EQ(BP(2, 7), BP(5, 7).getCompl());
   EXPECT_EQ(BP::getZero(), BP(7, 7).getCompl());
   EXPECT_EQ(BP::getOne(), BP(0, 7).getCompl());
 }
 
 TEST(BranchProbabilityTest, scale) {