Support: Add BranchProbability::scale() and ::scaleByInverse()

Add API to `BranchProbability` for scaling big integers.  Next job is to
rip the logic out of `BlockMass` and `BlockFrequency`.

llvm-svn: 207544

1 files changed, 68 insertions, 0 deletions

diff --git a/llvm/unittests/Support/BranchProbabilityTest.cpp b/llvm/unittests/Support/BranchProbabilityTest.cpp
index 56ab22334ca..b528728e8ae 100644
--- a/llvm/unittests/Support/BranchProbabilityTest.cpp
+++ b/llvm/unittests/Support/BranchProbabilityTest.cpp
@@ -87,4 +87,72 @@ TEST(BranchProbabilityTest, getCompl) {
   EXPECT_EQ(BP::getOne(), BP(0, 7).getCompl());
 }
 
+TEST(BranchProbabilityTest, scale) {
+  // Multiply by 1.0.
+  EXPECT_EQ(UINT64_MAX, BP(1, 1).scale(UINT64_MAX));
+  EXPECT_EQ(UINT64_MAX, BP(7, 7).scale(UINT64_MAX));
+  EXPECT_EQ(UINT32_MAX, BP(1, 1).scale(UINT32_MAX));
+  EXPECT_EQ(UINT32_MAX, BP(7, 7).scale(UINT32_MAX));
+  EXPECT_EQ(0u, BP(1, 1).scale(0));
+  EXPECT_EQ(0u, BP(7, 7).scale(0));
+
+  // Multiply by 0.0.
+  EXPECT_EQ(0u, BP(0, 1).scale(UINT64_MAX));
+  EXPECT_EQ(0u, BP(0, 1).scale(UINT64_MAX));
+  EXPECT_EQ(0u, BP(0, 1).scale(0));
+
+  auto Two63 = UINT64_C(1) << 63;
+  auto Two31 = UINT64_C(1) << 31;
+
+  // Multiply by 0.5.
+  EXPECT_EQ(Two63 - 1, BP(1, 2).scale(UINT64_MAX));
+
+  // Big fractions.
+  EXPECT_EQ(1u, BP(Two31, UINT32_MAX).scale(2));
+  EXPECT_EQ(Two31, BP(Two31, UINT32_MAX).scale(Two31 * 2));
+  EXPECT_EQ(Two63 + Two31, BP(Two31, UINT32_MAX).scale(UINT64_MAX));
+
+  // High precision.
+  EXPECT_EQ(UINT64_C(9223372047592194055),
+            BP(Two31 + 1, UINT32_MAX - 2).scale(UINT64_MAX));
+}
+
+TEST(BranchProbabilityTest, scaleByInverse) {
+  // Divide by 1.0.
+  EXPECT_EQ(UINT64_MAX, BP(1, 1).scaleByInverse(UINT64_MAX));
+  EXPECT_EQ(UINT64_MAX, BP(7, 7).scaleByInverse(UINT64_MAX));
+  EXPECT_EQ(UINT32_MAX, BP(1, 1).scaleByInverse(UINT32_MAX));
+  EXPECT_EQ(UINT32_MAX, BP(7, 7).scaleByInverse(UINT32_MAX));
+  EXPECT_EQ(0u, BP(1, 1).scaleByInverse(0));
+  EXPECT_EQ(0u, BP(7, 7).scaleByInverse(0));
+
+  // Divide by something very small.
+  EXPECT_EQ(UINT64_MAX, BP(1, UINT32_MAX).scaleByInverse(UINT64_MAX));
+  EXPECT_EQ(uint64_t(UINT32_MAX) * UINT32_MAX,
+            BP(1, UINT32_MAX).scaleByInverse(UINT32_MAX));
+  EXPECT_EQ(UINT32_MAX, BP(1, UINT32_MAX).scaleByInverse(1));
+
+  auto Two63 = UINT64_C(1) << 63;
+  auto Two31 = UINT64_C(1) << 31;
+
+  // Divide by 0.5.
+  EXPECT_EQ(UINT64_MAX - 1, BP(1, 2).scaleByInverse(Two63 - 1));
+  EXPECT_EQ(UINT64_MAX, BP(1, 2).scaleByInverse(Two63));
+
+  // Big fractions.
+  EXPECT_EQ(1u, BP(Two31, UINT32_MAX).scaleByInverse(1));
+  EXPECT_EQ(2u, BP(Two31 - 1, UINT32_MAX).scaleByInverse(1));
+  EXPECT_EQ(Two31 * 2 - 1, BP(Two31, UINT32_MAX).scaleByInverse(Two31));
+  EXPECT_EQ(Two31 * 2 + 1, BP(Two31 - 1, UINT32_MAX).scaleByInverse(Two31));
+  EXPECT_EQ(UINT64_MAX, BP(Two31, UINT32_MAX).scaleByInverse(Two63 + Two31));
+
+  // High precision.  The exact answers to these are close to the successors of
+  // the floor.  If we were rounding, these would round up.
+  EXPECT_EQ(UINT64_C(18446744065119617030),
+            BP(Two31 + 2, UINT32_MAX - 2)
+                .scaleByInverse(UINT64_C(9223372047592194055)));
+  EXPECT_EQ(UINT64_C(18446744065119617026),
+            BP(Two31 + 1, UINT32_MAX).scaleByInverse(Two63 + Two31));
+}
+
 }