[clang] [CIR] Fix lost catch clauses on EH landing pads (PR #205638)

[via cfe-commits]

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@@ -325,19 +374,47 @@ mlir::LogicalResult ItaniumEHLowering::lowerFunc(cir::FuncOp funcOp) {
   if (!funcOp.getPersonality())
     funcOp.setPersonality(kGxxPersonality);
 
-  // Lower each initiate and all EH ops connected to it. The token map is
-  // shared across all initiate operations. Multiple initiates may flow into the
-  // same dispatch block, and the map ensures the arguments are registered
-  // only once. Dispatch ops are scheduled for deferred removal so that sibling
-  // initiates can still read catch types from a shared dispatch.
+  // Compute, read-only and before any destructive lowering, the dispatches each
+  // initiate's exception can reach (innermost first; more than one for nested
+  // try/catch).  A landing pad's catch types are a property of the EH graph, so
+  // deriving them here keeps them independent of the order in which the
+  // destructive per-initiate traversal in lowerEhInitiate tears down shared
+  // token-graph edges.  Otherwise a sibling or outer dispatch could be missed,
+  // leaving a landing pad without its catch clause (it would resume past the
+  // handler to std::terminate) or an un-lowered leftover dispatch.
+  llvm::DenseMap<mlir::Operation *, SmallVector<cir::EhDispatchOp>>
+      reachedDispatches;
+  llvm::DenseMap<mlir::Operation *, bool> reachesCleanup;
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adams381 wrote:

Combined into one `InitiateEHInfo` map keyed by the initiate op.

https://github.com/llvm/llvm-project/pull/205638