[llvm] [SimplifyCFG] Simplify switch instruction that has duplicate arms (PR #114262)

[Nikita Popov via llvm-commits]

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@@ -7436,6 +7437,140 @@ static bool simplifySwitchOfCmpIntrinsic(SwitchInst *SI, IRBuilderBase &Builder,
   return true;
 }
 
+namespace llvm {
+template <> struct DenseMapInfo<const SwitchInst::CaseHandle *> {
+  static const SwitchInst::CaseHandle *getEmptyKey() {
+    return reinterpret_cast<const SwitchInst::CaseHandle *>(
+        DenseMapInfo<void *>::getEmptyKey());
+  }
+  static const SwitchInst::CaseHandle *getTombstoneKey() {
+    return reinterpret_cast<const SwitchInst::CaseHandle *>(
+        DenseMapInfo<void *>::getTombstoneKey());
+  }
+  static unsigned getHashValue(const SwitchInst::CaseHandle *Case) {
+    BasicBlock *Succ = Case->getCaseSuccessor();
+    BranchInst *BI = cast<BranchInst>(Succ->getTerminator());
+
+    auto It = BI->successors();
+    return hash_combine(Succ->size(), hash_combine_range(It.begin(), It.end()));
+  }
+  static bool isEqual(const SwitchInst::CaseHandle *LHS,
+                      const SwitchInst::CaseHandle *RHS) {
+
+    auto EKey = DenseMapInfo<const SwitchInst::CaseHandle *>::getEmptyKey();
+    auto TKey = DenseMapInfo<const SwitchInst::CaseHandle *>::getTombstoneKey();
+    if (LHS == EKey || RHS == EKey || LHS == TKey || RHS == TKey)
+      return LHS == RHS;
+
+    auto IsBranchEq = [](BranchInst *A, BranchInst *B) {
+      if (A->isConditional() != B->isConditional())
+        return false;
+
+      if (A->isConditional()) {
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nikic wrote:

Why is this code handling conditional branches? As far as I can tell, your motivating case and all test cases use unconditional branches.

https://github.com/llvm/llvm-project/pull/114262