[mono][interp] Disable inlining of methods that always throw #122587
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When inlining, we create a placeholder exit_bb that is branched to whenever the inlined method returns. When this bblock was not reachable, it was leading to some inconsistent CFG state. This is relatively easy to fix but, if exit_bb is dead, it means that the method is always throwing an exception. We shouldn't bother inlining such methods in the first place, since they are not part of hot code paths.
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Tagging subscribers to this area: @BrzVlad, @kotlarmilos |
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Pull request overview
This PR improves the Mono interpreter's inlining logic by preventing the inlining of methods that always throw exceptions. Previously, when a method's exit basic block was unreachable (indicated by exit_bb->in_count == 0), it was simply marked as dead, which could lead to inconsistent CFG (control flow graph) state. The fix recognizes that such methods are not performance-sensitive and should not be inlined in the first place.
- Changed behavior from marking unreachable exit blocks as dead to failing the inline attempt for methods that always throw
- Updated comment to clarify the rationale: methods that always throw are not performance-sensitive code paths
kotlarmilos
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Dec 16, 2025
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/backport to release/10.0 |
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Started backporting to |
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jeffhandley
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Jan 8, 2026
… throw (#122594) Backport of #122587 to release/10.0 /cc @BrzVlad ## Customer Impact - [x] Customer reported - [ ] Found internally Customer reported that app on blazor wasm hangs. Compiling methods that call throw helper methods (methods that always throw) with mono interpreter can lead to hangs in the runtime. MAUI ios can also be impacted in theory. ## Regression - [x] Yes - [ ] No This a regression from .NET9. Seems like the issue started happening after #108731. ## Testing Verified with sample repro provided by customer. ## Risk Low. The fix aborts inlining in methods that throw unconditionally. The common mechanism of inline abort is reused so there is no added risk here. Co-authored-by: Vlad Brezae <brezaevlad@gmail.com>
This was referenced Jan 9, 2026
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When inlining, we create a placeholder exit_bb that is branched to whenever the inlined method returns. When this bblock was not reachable, it was leading to some inconsistent CFG state. This is relatively easy to fix but, if exit_bb is dead, it means that the method is always throwing an exception. We shouldn't bother inlining such methods in the first place, since they are not part of hot code paths.
Fixes #122529