Add a test

Author: chapuni

llvm/unittests/ProfileData/CoverageMappingTest.cpp

@@ -291,6 +291,45 @@ struct CoverageMappingTest : ::testing::TestWithParam<std::tuple<bool, bool>> {
   }
 };
 
+TEST(CoverageMappingTest, expression_subst) {
+  CounterExpressionBuilder Builder;
+  CounterExpressionBuilder::SubstMap MapToExpand;
+
+  auto C = [](unsigned ID) { return Counter::getCounter(ID); };
+  auto A = [&](Counter LHS, Counter RHS) { return Builder.add(LHS, RHS); };
+  // returns {E, N} in clangCodeGen
+  auto getBranchCounterPair = [&](Counter E, Counter P, Counter N) {
+    auto Skipped = Builder.subtract(P, E);
+    MapToExpand[N] = Builder.subst(Skipped, MapToExpand);
+  };
+
+  auto E18 = C(5);
+  auto P18 = C(2);
+  auto S18 = C(18);
+  // #18 => (#2 - #5)
+  getBranchCounterPair(E18, P18, S18);
+
+  auto E22 = S18;
+  auto P22 = C(0);
+  auto S22 = C(22);
+  // #22 => #0 - (#2 - #5)
+  getBranchCounterPair(E22, P22, S22);
+
+  auto E28 = A(A(C(9), C(11)), C(14));
+  auto P28 = S22;
+  auto S28 = C(28);
+  // #28 => (((((#0 + #5) - #2) - #9) - #11) - #14)
+  getBranchCounterPair(E28, P28, S28);
+
+  auto LHS = A(E28, A(S28, S18));
+  auto RHS = C(0);
+
+  // W/o subst, LHS cannot be reduced.
+  ASSERT_FALSE(Builder.subtract(LHS, RHS).isZero());
+  // W/ subst, C(18) and C(28) in LHS will be reduced.
+  ASSERT_TRUE(Builder.subst(Builder.subtract(LHS, RHS), MapToExpand).isZero());
+}
+
 TEST_P(CoverageMappingTest, basic_write_read) {
   startFunction("func", 0x1234);
   addCMR(Counter::getCounter(0), "foo", 1, 1, 1, 1);