BlockFrequency: Saturate at 1 instead of 0 when multiplying a frequency with a branch probability.
Zero is used by BlockFrequencyInfo as a special "don't know" value. It also
causes a sink for frequencies as you can't ever get off a zero frequency with
more multiplies.
This recovers a 10% regression on MultiSource/Benchmarks/7zip. A zero frequency
was propagated into an inner loop causing excessive spilling.
PR16402.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@184584 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/unittests/Support/BlockFrequencyTest.cpp b/unittests/Support/BlockFrequencyTest.cpp
index ff66bc4..bcb88c8 100644
--- a/unittests/Support/BlockFrequencyTest.cpp
+++ b/unittests/Support/BlockFrequencyTest.cpp
@@ -8,11 +8,22 @@
namespace {
+TEST(BlockFrequencyTest, ZeroToZero) {
+ BlockFrequency Freq(0);
+ BranchProbability Prob(UINT32_MAX - 1, UINT32_MAX);
+ Freq *= Prob;
+ EXPECT_EQ(Freq.getFrequency(), 0u);
+
+ Freq = 1;
+ Freq *= BranchProbability::getZero();
+ EXPECT_EQ(Freq.getFrequency(), 0u);
+}
+
TEST(BlockFrequencyTest, OneToZero) {
BlockFrequency Freq(1);
BranchProbability Prob(UINT32_MAX - 1, UINT32_MAX);
Freq *= Prob;
- EXPECT_EQ(Freq.getFrequency(), 0u);
+ EXPECT_EQ(Freq.getFrequency(), 1u);
}
TEST(BlockFrequencyTest, OneToOne) {