[llvm] [ADT] Teach set_intersect to erase with iterators (PR #99569)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-adt

Author: Kazu Hirata (kazutakahirata)

<details>
<summary>Changes</summary>

Without this patch, we erase an element in S1 by value even though we
have an interator pointing to it.  This patch tries to use erase(iter)
to avoid redundant lookups.

Existing tests cover the new code path.  Somewhat worrying is that the
existing "erase-by-value" code path is no longer covered.  I am not
aware of any container that has erase(value) but not remove_if or
erase(iter).


---
Full diff: https://github.com/llvm/llvm-project/pull/99569.diff


1 Files Affected:

- (modified) llvm/include/llvm/ADT/SetOperations.h (+7) 


``````````diff
diff --git a/llvm/include/llvm/ADT/SetOperations.h b/llvm/include/llvm/ADT/SetOperations.h
index 2b1a103565f7d..feb3561aca61f 100644
--- a/llvm/include/llvm/ADT/SetOperations.h
+++ b/llvm/include/llvm/ADT/SetOperations.h
@@ -60,6 +60,13 @@ template <class S1Ty, class S2Ty> void set_intersect(S1Ty &S1, const S2Ty &S2) {
   auto Pred = [&S2](const auto &E) { return !S2.count(E); };
   if constexpr (detail::HasMemberRemoveIf<S1Ty, decltype(Pred)>) {
     S1.remove_if(Pred);
+  } else if constexpr (detail::HasMemberEraseIter<S1Ty>) {
+    typename S1Ty::iterator Next;
+    for (typename S1Ty::iterator I = S1.begin(); I != S1.end(); I = Next) {
+      Next = std::next(I);
+      if (!S2.count(*I))
+        S1.erase(I); // Erase element if not in S2
+    }
   } else {
     for (typename S1Ty::iterator I = S1.begin(); I != S1.end();) {
       const auto &E = *I;

``````````

</details>


https://github.com/llvm/llvm-project/pull/99569