================
@@ -0,0 +1,1243 @@
+=============================================
+ClangIR Cleanup and Exception Handling Design
+=============================================
+
+.. contents::
+ :local:
+
+Overview
+========
+
+This document describes the proposed new design for C++ cleanups and exception
+handling representation and lowering in the CIR dialect. The initial CIR
+generation will follow the general structure of the cleanup and exception
+handling code in Clang's LLVM IR generation. In particular, we will continue
+to use the ``EHScopeStack`` with pushing and popping of
``EHScopeStack::Cleanup``
+objects to drive the creation of cleanup scopes within CIR.
+
+However, the LLVM IR generated by Clang is fundamentally unstructured and
+therefore isn't well suited to the goals of CIR. Therefore, we are proposing
+a high-level representation that follows MLIR's structured control flow model.
+
+The ``cir::LowerCFG`` pass will lower this high-level representation to a
+different form where control flow is block-based and explicit. This form will
+more closely resemble the LLVM IR used when Clang is generating LLVM IR
+directly. However, this form will still be ABI-agnostic.
+
+An additional pass will be introduced to lower the flattened form to an
+ABI-specific representation. This ABI-specific form will have a direct
+correspondence to the LLVM IR exception handling representation for a given
+target.
+
+High-level CIR representation
+==============================
+
+Normal and EH cleanups
+----------------------
+Scopes that require normal or EH cleanup will be represented using a new
+operation, ``cir.cleanup.scope``.
+
+.. code-block::
+
+ cir.cleanup.scope {
+ // body region
+ } cleanup [eh_only] {
+ // cleanup instructions
+ }
+
+Execution begins with the first operation in the body region and continues
+according to normal control flow semantics until a terminating operation
+(``cir.yield``, ``cir.break``, ``cir.return``) is encountered or an exception
is
----------------
rnk wrote:
How does CIR model the other non-local control flow operations, `goto` and
computed `goto` / `indirectbr`? Does the CIR verifier reject erroneous cases
like jumping into a cleanup scope, or jumping into a statement expression?
I guess what should happen here is that the frontend rejects such cases, and
the verifier should reject such cases as well.
https://github.com/llvm/llvm-project/pull/177625
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