[llvm] [NFC][RemoveDIs] Switch constant-hoisting to insert with iterators (PR #84738)

[Scott Todd via llvm-commits]

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@@ -774,6 +774,32 @@ BasicBlock::iterator skipDebugIntrinsics(BasicBlock::iterator It);
 inline void BasicBlock::validateInstrOrdering() const {}
 #endif
 
+// Specialize DenseMapInfo for iterators, so that ththey can be installed into
+// maps and sets. The iterator is made up of its node pointer, and the
+// debug-info "head" bit.
+template <> struct DenseMapInfo<BasicBlock::iterator> {
+  static inline BasicBlock::iterator getEmptyKey() {
+    return BasicBlock::iterator(nullptr);
+  }
+
+  static inline BasicBlock::iterator getTombstoneKey() {
+    BasicBlock::iterator It(nullptr);
+    It.setHeadBit(true);
+    return It;
+  }
+
+  static unsigned getHashValue(const BasicBlock::iterator &It) {
+    return DenseMapInfo<void *>::getHashValue(
+               reinterpret_cast<void *>(It.getNodePtr())) ^
+           It.getHeadBit();
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ScottTodd wrote:

Ah, there are PRs for that already.

https://github.com/llvm/llvm-project/pull/84738