[ADT] Add set_intersects to check if there is any intersection

[teresajohnson]

Add a facility to check if there is any intersection between 2 sets.
This will be used in some follow on changes to MemProf.

[llvmbot]

@llvm/pr-subscribers-llvm-adt

Author: Teresa Johnson (teresajohnson)

Changes

Add a facility to check if there is any intersection between 2 sets.
This will be used in some follow on changes to MemProf.

---

Full diff: https://github.com/llvm/llvm-project/pull/127907.diff

2 Files Affected:

• (modified) llvm/include/llvm/ADT/SetOperations.h (+17)
• (modified) llvm/unittests/ADT/SetOperationsTest.cpp (+11)

diff --git a/llvm/include/llvm/ADT/SetOperations.h b/llvm/include/llvm/ADT/SetOperations.h
index 86a27b683ebc1..4eef3727a97bb 100644
--- a/llvm/include/llvm/ADT/SetOperations.h
+++ b/llvm/include/llvm/ADT/SetOperations.h
@@ -157,6 +157,23 @@ bool set_is_subset(const S1Ty &S1, const S2Ty &S2) {
   return true;
 }
 
+template <class S1Ty, class S2Ty>
+bool set_intersects_impl(const S1Ty &S1, const S2Ty &S2) {
+  for (const auto &E : S1)
+    if (S2.count(E))
+      return true;
+  return false;
+}
+
+/// set_intersects(A, B) - Return true iff A ^ B is non empty
+template <class S1Ty, class S2Ty>
+bool set_intersects(const S1Ty &S1, const S2Ty &S2) {
+  if (S1.size() < S2.size())
+    return set_intersects_impl(S1, S2);
+  else
+    return set_intersects_impl(S2, S1);
+}
+
 } // namespace llvm
 
 #endif
diff --git a/llvm/unittests/ADT/SetOperationsTest.cpp b/llvm/unittests/ADT/SetOperationsTest.cpp
index f99f5c9b2af10..84691b08dd4f4 100644
--- a/llvm/unittests/ADT/SetOperationsTest.cpp
+++ b/llvm/unittests/ADT/SetOperationsTest.cpp
@@ -273,4 +273,15 @@ TEST(SetOperationsTest, SetIsSubset) {
   EXPECT_FALSE(set_is_subset(Set1, Set2));
 }
 
+TEST(SetOperationsTest, SetIntersects) {
+  std::set<int> Set1 = {1, 2, 3, 4};
+  std::set<int> Set2 = {3, 4, 5};
+  EXPECT_TRUE(set_intersects(Set1, Set2));
+  EXPECT_TRUE(set_intersects(Set2, Set1));
+
+  Set2 = {5, 6, 7};
+  EXPECT_FALSE(set_intersects(Set1, Set2));
+  EXPECT_FALSE(set_intersects(Set2, Set1));
+}
+
 } // namespace

[snehasish]

lgtm

[kuhar]

nit: no else after return https://llvm.org/docs/CodingStandards.html#don-t-use-else-after-a-return (unless with if constexpr)

[teresajohnson]

done

[kuhar]

Could you also add a testcase with empty sets (the usual source of edge cases)?

[teresajohnson]

done

[kuhar]

Consider putting this in a detail namespace

[teresajohnson]

done

[teresajohnson]

Thanks for the review

[teresajohnson]

done

[teresajohnson]

done

[teresajohnson]

done