[clang] [CIR] Fix remaining (part 2) FlattenCFG rewriter contract violations (PR #192503)

[Erich Keane via cfe-commits]

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@@ -228,13 +228,19 @@ class CIRSwitchOpFlattening : public mlir::OpRewritePattern<cir::SwitchOp> {
   mlir::LogicalResult
   matchAndRewrite(cir::SwitchOp op,
                   mlir::PatternRewriter &rewriter) const override {
-    // Cleanup scopes must be lowered before the enclosing switch so that
-    // break inside them is properly routed through cleanup.
-    // Fail the match so the pattern rewriter will process cleanup scopes first.
-    bool hasNestedCleanup = op->walk([&](cir::CleanupScopeOp) {
-                                return mlir::WalkResult::interrupt();
-                              }).wasInterrupted();
-    if (hasNestedCleanup)
+    // All nested structured CIR ops must be flattened before the switch.
+    // Break statements inside nested structured ops (scopes, ifs, ternaries,
+    // cleanup scopes) would create branches to blocks outside those ops'
+    // regions, which is invalid. Fail the match so the pattern rewriter will
+    // process them first.
+    bool hasNestedStructuredOps =
+        op->walk([&](mlir::Operation *nestedOp) {
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erichkeane wrote:

Should this be its own function?  I'd hate for these scopes to get out of sync.

https://github.com/llvm/llvm-project/pull/192503