[Wasm RyuJit] eh flow by AndyAyersMS · Pull Request #125594 · dotnet/runtime

AndyAyersMS · 2026-03-16T00:28:04Z

Implements much of the control flow needed to support resuming control in a method after an exception is caught.

See #121178 (comment) for a sketch of the approach implemented here.

Overview of the changes:

a new phase fgWasmEhFlow that runs before Lower that makes the "continuation flow" for try/catch explicit in the method flow graph and IR.
a "lightweight" abstraction over the try regions in the method that enables walking the try region body in RPO
updates to the core layout algorithm to keep try regions that will inspire Wasm try_table protection contiguous in the block order. For cases where a try region begins in a loop but extends outside the loop, we extend the end of the Wasm loop to encompass the try.
codegen for try_table, still a bit incomplete; it currently catches all exceptions and does not do proper rethrow.
introduction of a control variable to steer execution to the proper continuation on catch resumption. This will likely evolve into the Virtual IP in some way. It is also ultimately going to be settable by the runtime to signal that particular stack frames will not catch the current exception.

…ol variable yet

…ter on

…ethrow...)

…lid tag index

…ed loop

Copilot

Pull request overview

This PR extends the WASM JIT pipeline to start modeling WebAssembly exception-handling (EH) control flow explicitly, including new wasm instruction/value types and new IR/control-flow structures needed to emit try_table/catch_ref patterns.

Changes:

Add wasm EH surface area: exnref value type, try_table/catch_ref/throw_ref instructions, and emitter support for encoding try_table and catch clauses.
Introduce wasm-specific IR nodes/flags (GT_WASM_IF_EXCEPT, GT_WASM_THROW_REF, GTF_JTRUE_WASM_EH) and integrate them into core GenTree helpers.
Add a new WASM phase (PHASE_WASM_EH_FLOW) plus try-region enumeration and a try-aware+loop-aware RPO walk to support structured wasm codegen.

Reviewed changes

Copilot reviewed 20 out of 20 changed files in this pull request and generated 9 comments.

Show a summary per file

File	Description
src/coreclr/jit/registeropswasm.h / .cpp	Add `ExnRef` wasm value type + name mapping
src/coreclr/jit/instrswasm.h	Add wasm EH opcodes (`try_table`, `catch_ref`, `throw_ref`)
src/coreclr/jit/emitfmtswasm.h	Add new instruction formats for `TRY_TABLE` / `CATCH_DECL`
src/coreclr/jit/emit.h	Add `instrDescValTypeImm` and format query for `try_table` encoding
src/coreclr/jit/emitwasm.h / .cpp	Add `emitIns_Ty_I` and encoder support for `try_table` + catch decls
src/coreclr/jit/gtlist.h	Add wasm-specific IR nodes
src/coreclr/jit/gentree.h / .cpp	Add wasm JTRUE flag + plumb new nodes through GenTree infrastructure
src/coreclr/jit/jiteh.cpp	Add helper to find outermost mutual-protect try region
src/coreclr/jit/flowgraph.cpp	Adjust throw-helper placement for wasm; add try-region data structures
src/coreclr/jit/compiler.h / compiler.hpp	Declare try-region APIs + add try-aware loop-aware RPO visitor
src/coreclr/jit/fgwasm.h / .cpp	Add try intervals and new `fgWasmEhFlow()` phase building explicit post-catch dispatch
src/coreclr/jit/compiler.cpp / compphases.h	Wire in the new WASM EH flow phase
src/coreclr/jit/codegenwasm.cpp	Emit `try_table`/`catch_ref` at block start; suppress codegen for wasm-EH-marked JTRUE
src/coreclr/jit/fgopt.cpp	Minor preprocessor consistency tweak

You can also share your feedback on Copilot code review. Take the survey.

src/coreclr/jit/fgwasm.cpp

src/coreclr/jit/emitwasm.cpp

src/coreclr/jit/jiteh.cpp

src/coreclr/jit/compiler.hpp

src/coreclr/jit/emitwasm.cpp

src/coreclr/jit/codegenwasm.cpp

src/coreclr/jit/fgwasm.cpp

…atch

…low processing

Copilot

Pull request overview

This PR adds initial infrastructure for explicit exception-handling (EH) continuation flow in the Wasm JIT pipeline, including new IR nodes and Wasm instruction/emitter support to enable try_table-based dispatch for catch continuations.

Changes:

Introduces Wasm-specific IR nodes (GT_WASM_JEXCEPT, GT_WASM_THROW_REF) and wires them into liveness/IR utilities.
Adds a new Wasm EH flow phase (PHASE_WASM_EH_FLOW) that materializes post-catch continuation dispatch via conditional entry blocks, switches, and rethrow blocks.
Extends Wasm codegen/emitter/instruction metadata with try_table, catch_ref, throw_ref, and exnref support.

Reviewed changes

Copilot reviewed 21 out of 21 changed files in this pull request and generated 11 comments.

Show a summary per file

File	Description
src/coreclr/jit/registeropswasm.h	Adds `WasmValueType::ExnRef`.
src/coreclr/jit/registeropswasm.cpp	Adds `"exnref"` name mapping.
src/coreclr/jit/liveness.cpp	Treats `GT_WASM_JEXCEPT` as always side-effecting (non-removable).
src/coreclr/jit/instrswasm.h	Adds Wasm EH-related pseudo/real instructions (`catch_ref`, `try_table`, `throw_ref`).
src/coreclr/jit/gtlist.h	Adds new Wasm-specific GT node kinds.
src/coreclr/jit/gentree.h	Treats `GT_WASM_JEXCEPT` as a conditional-jump-like node.
src/coreclr/jit/gentree.cpp	Wires new GT nodes into comparison/use/exception/clone/dump paths.
src/coreclr/jit/flowgraph.cpp	Alters throw-helper placement for Wasm; adds `FlowGraphTryRegions` implementation.
src/coreclr/jit/fgwasm.h	Extends `WasmInterval` to support Try intervals (in addition to Block/Loop).
src/coreclr/jit/fgwasm.cpp	Adds `fgWasmEhFlow` + try-aware traversal and interval creation for try regions.
src/coreclr/jit/fgstmt.cpp	Marks `GT_WASM_JEXCEPT` as control-flow.
src/coreclr/jit/fgopt.cpp	Minor preprocessor consistency fix for Wasm switch assertion.
src/coreclr/jit/emitwasm.h	Adds emitter APIs for (type, imm) encoding used by `try_table`.
src/coreclr/jit/emitwasm.cpp	Implements encoding/size/printing for `try_table` and catch declarations; adds `exnref` type code.
src/coreclr/jit/emitfmtswasm.h	Adds new Wasm instruction formats (`IF_TRY_TABLE`, `IF_CATCH_DECL`).
src/coreclr/jit/emit.h	Adds a new instrDesc type to carry (valtype, imm) for `try_table`.
src/coreclr/jit/compphases.h	Adds new phase name `PHASE_WASM_EH_FLOW`.
src/coreclr/jit/compiler.hpp	Adds try-aware loop-aware RPO walker and try-region block visitor.
src/coreclr/jit/compiler.h	Declares `FlowGraphTryRegions` APIs and Wasm EH flow entry points.
src/coreclr/jit/compiler.cpp	Inserts Wasm EH flow phase before unreachable removal and SCC transforms.
src/coreclr/jit/codegenwasm.cpp	Emits `try_table`/`catch_ref` for Try intervals; adds handling stubs for new GT nodes.

You can also share your feedback on Copilot code review. Take the survey.

src/coreclr/jit/codegenwasm.cpp

src/coreclr/jit/fgwasm.cpp

AndyAyersMS · 2026-03-17T21:58:10Z

@dotnet/jit-contrib FYI

Not sure will wants to review this one. Any volunteers?

This runs through a cross-crossgen of an x86 crossgen SPMI without asserting but is otherwise difficult to test (eg the Wasm cannot be validated yet as funclet codegen is mixed in with the main function).

jakobbotsch · 2026-03-17T22:05:10Z

Not sure will wants to review this one. Any volunteers?

I can take a look.

Copilot

Pull request overview

Implements the initial end-to-end plumbing for Wasm exception resumption control flow in RyuJIT by making post-catch continuation dispatch explicit in the CFG/IR, and extending Wasm control-flow interval/layout + emission to support try_table-based protection/dispatch.

Changes:

Add fgWasmEhFlow phase to materialize catch-resumption dispatch (control var + per-try switch/rethrow blocks + special GT_WASM_JEXCEPT/GT_WASM_THROW_REF nodes).
Introduce FlowGraphTryRegions / FlowGraphTryRegion and use them to build try-aware + loop-aware RPO and to create Wasm Try intervals.
Extend Wasm emitter/instruction tables/value types and codegen to start emitting try_table + catch_ref scaffolding.

Reviewed changes

Copilot reviewed 21 out of 21 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
src/coreclr/jit/registeropswasm.h	Add `WasmValueType::ExnRef`.
src/coreclr/jit/registeropswasm.cpp	Add name mapping for `exnref`.
src/coreclr/jit/liveness.cpp	Treat `GT_WASM_JEXCEPT` as non-removable side-effecting node.
src/coreclr/jit/instrswasm.h	Add `catch_ref`, `throw_ref`, and `try_table` pseudo/real instructions.
src/coreclr/jit/gtlist.h	Introduce `GT_WASM_JEXCEPT` and `GT_WASM_THROW_REF` nodes.
src/coreclr/jit/gentree.h	Treat `GT_WASM_JEXCEPT` as a conditional-jump operator.
src/coreclr/jit/gentree.cpp	Wire new Wasm nodes into comparison/use-iteration/exceptions/cloning/printing helpers.
src/coreclr/jit/flowgraph.cpp	Wasm-specific throw-helper placement tweak; add `FlowGraphTryRegions` implementation.
src/coreclr/jit/fgwasm.h	Extend Wasm intervals with `Kind::{Block,Loop,Try}`.
src/coreclr/jit/fgwasm.cpp	Add `fgWasmEhFlow`; build try regions; create `Try` intervals; try-aware loop-aware RPO.
src/coreclr/jit/fgstmt.cpp	Treat `GT_WASM_JEXCEPT` as control-flow for statement removal logic.
src/coreclr/jit/fgopt.cpp	Minor wasm-specific assert guard cleanup.
src/coreclr/jit/emitwasm.h	Add emitter APIs for `<valtype, imm>` encoding (for `try_table`).
src/coreclr/jit/emitwasm.cpp	Implement `try_table`/`catch_ref` sizing + output + disasm plumbing; add `exnref` type code.
src/coreclr/jit/emitfmtswasm.h	Add `TRY_TABLE` and `CATCH_DECL` formats.
src/coreclr/jit/emit.h	Add `instrDescValTypeImm` and helper predicate for wasm `try_table` descriptor.
src/coreclr/jit/compphases.h	Add `PHASE_WASM_EH_FLOW`.
src/coreclr/jit/compiler.hpp	Implement try-aware loop-aware RPO; implement `VisitTryRegionBlocksReversePostOrder`.
src/coreclr/jit/compiler.h	Declare try-region types + new wasm phase helpers.
src/coreclr/jit/compiler.cpp	Insert `PHASE_WASM_EH_FLOW` before wasm DFS cleanup/SCC transform.
src/coreclr/jit/codegenwasm.cpp	Begin emitting `try_table`/`catch_ref` for `Try` intervals; stub wasm EH catchret; add node handling.

You can also share your feedback on Copilot code review. Take the survey.

src/coreclr/jit/fgwasm.cpp

src/coreclr/jit/codegenwasm.cpp

src/coreclr/jit/fgwasm.cpp

src/coreclr/jit/flowgraph.cpp

jakobbotsch

This looks good to me on a first pass.... I'll probably give it another look over on Friday to try to internalize some of the EH concepts a little bit more.

…umption

Copilot

Pull request overview

Adds initial Wasm-specific exception-handling continuation control-flow support in the CoreCLR JIT, making catch-resumption paths explicit in the CFG/IR and extending Wasm control-flow layout + emission to begin representing EH using try_table.

Changes:

Introduces fgWasmEhFlow to materialize post-catch resumption dispatch via a control variable, switch blocks, and a Wasm-specific conditional jump marker node.
Adds FlowGraphTryRegions and integrates a try-aware + loop-aware RPO visitation, plus interval kinds for Try in Wasm CFG lowering.
Extends Wasm emitter/instruction set to support try_table / catch declarations and updates Wasm codegen to emit them.

Reviewed changes

Copilot reviewed 21 out of 21 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
src/coreclr/jit/registeropswasm.h	Adds `ExnRef` value type for Wasm emission.
src/coreclr/jit/registeropswasm.cpp	Adds string name mapping for `exnref`.
src/coreclr/jit/liveness.cpp	Marks `GT_WASM_JEXCEPT` as side-effecting to prevent removal.
src/coreclr/jit/instrswasm.h	Adds Wasm instructions/pseudo-instructions for `try_table`, catch decls, and `throw_ref`.
src/coreclr/jit/gtlist.h	Introduces Wasm-specific IR nodes (`GT_WASM_JEXCEPT`, `GT_WASM_THROW_REF`).
src/coreclr/jit/gentree.h	Treats `GT_WASM_JEXCEPT` as a conditional jump opcode.
src/coreclr/jit/gentree.cpp	Hooks new Wasm IR nodes into core GenTree utilities (compare/clone/iterator/exceptions/display).
src/coreclr/jit/flowgraph.cpp	Adjusts throw-helper placement for Wasm; adds `FlowGraphTryRegions` implementation.
src/coreclr/jit/fgwasm.h	Extends `WasmInterval` to include `Try` kind and related helpers.
src/coreclr/jit/fgwasm.cpp	Adds try-aware layout/interval handling and implements `fgWasmEhFlow` + dispatch block generation.
src/coreclr/jit/fgstmt.cpp	Treats `GT_WASM_JEXCEPT` as control flow.
src/coreclr/jit/fgopt.cpp	Fixes `TARGET_WASM` preprocessor usage for switch assertion.
src/coreclr/jit/emitwasm.h	Adds emitter APIs for value-type+immediate instruction descriptors.
src/coreclr/jit/emitwasm.cpp	Implements encoding/size/printing for `try_table` and catch decl pseudo-instructions.
src/coreclr/jit/emitfmtswasm.h	Adds new Wasm instruction formats for `TRY_TABLE` and `CATCH_DECL`.
src/coreclr/jit/emit.h	Adds `instrDescValTypeImm` and helpers for Wasm emission.
src/coreclr/jit/compphases.h	Adds the new `PHASE_WASM_EH_FLOW` phase.
src/coreclr/jit/compiler.hpp	Adds try-aware+loop-aware RPO visitor and try-region block visitation helper.
src/coreclr/jit/compiler.h	Declares try-region types and Wasm EH flow entry points.
src/coreclr/jit/compiler.cpp	Wires `fgWasmEhFlow` into the Wasm compilation pipeline before unreachable-block removal.
src/coreclr/jit/codegenwasm.cpp	Emits `try_table`/catch decls on interval start; adds Wasm EH IR handling and no-op catchret codegen.

You can also share your feedback on Copilot code review. Take the survey.

src/coreclr/jit/emitwasm.cpp

src/coreclr/jit/codegenwasm.cpp

src/coreclr/jit/fgwasm.cpp

src/coreclr/jit/flowgraph.cpp

jakobbotsch

LGTM again. Simplification really helps.
A few clarifying questions.

AndyAyersMS · 2026-03-20T15:01:27Z

/ba-g unrelated build failures

AndyAyersMS added 18 commits March 9, 2026 18:30

checkpoint -- have the control flow bit in, but not setting the contr…

b36762c

…ol variable yet

don't optimize these switches; assert if we see unreachable via EH la…

7ece6c7

…ter on

revise to be try-relative; local continuation numbers (0 normal, -1 r…

0e93714

…ethrow...)

try aware + loop aware RPO

6b40408

slightly better dumping; start thinking of how to find the loop ends

5fc8e64

handle deferred loop end; don't optimize away the eh switch

538eb51

Merge branch 'main' into WasmEHFlow

c1d74e6

checkpoint, working on emitter

20d589a

not totally broken

9b84d4f

new ir nodes; rethrow

c136719

wrapping block sig, temporarily use catch_all_ref to avoid needing va…

218b167

…lid tag index

cleanup

4123192

fixes

9817830

fix switch codegen

356cd48

fix switch block region

b410fb7

fix try region nesting

29c78b9

for a try region, exclude blocks that are in handlers within the try

2160be7

really skip funclet entries; last block in loop must not be in a nest…

a7dc48a

…ed loop

Copilot AI review requested due to automatic review settings March 16, 2026 00:28

github-actions bot added the area-CodeGen-coreclr CLR JIT compiler in src/coreclr/src/jit and related components such as SuperPMI label Mar 16, 2026

dotnet-policy-service bot assigned AndyAyersMS Mar 16, 2026

Copilot started reviewing on behalf of AndyAyersMS March 16, 2026 00:29 View session

Copilot AI reviewed Mar 16, 2026

View reviewed changes

jkotas added the arch-wasm WebAssembly architecture label Mar 16, 2026

AndyAyersMS added 2 commits March 16, 2026 11:32

fix linux build; review feedback; start to handle non-resumable try/c…

12d5895

…atch

handle try/catch that cannot resume in the method

f6583d6

This was referenced Mar 17, 2026

XHarness package install failure on iOS due to devicectl NSPOSIXErrorDomain error 49 #123796

Open

MsQuic fails with QUIC_STATUS_OUT_OF_MEMORY on AzureLinux #123216

Open

AndyAyersMS added 2 commits March 16, 2026 19:56

handle resumptions in other handler regions

bcc36a7

handle case where we have a one-block try that gets split during eh f…

f76c887

…low processing

Copilot AI review requested due to automatic review settings March 17, 2026 21:12

Copilot started reviewing on behalf of AndyAyersMS March 17, 2026 21:13 View session

Copilot AI reviewed Mar 17, 2026

View reviewed changes

fix spelling issues

c5d970f

AndyAyersMS marked this pull request as ready for review March 17, 2026 21:57

Copilot AI review requested due to automatic review settings March 17, 2026 21:57

Copilot started reviewing on behalf of AndyAyersMS March 17, 2026 21:58 View session

jakobbotsch self-requested a review March 17, 2026 22:04

Copilot AI reviewed Mar 17, 2026

View reviewed changes

review feedback

8b5aa99

jakobbotsch reviewed Mar 18, 2026

View reviewed changes

src/coreclr/jit/fgwasm.cpp Show resolved Hide resolved

jakobbotsch reviewed Mar 18, 2026

View reviewed changes

src/coreclr/jit/fgwasm.cpp Outdated Show resolved Hide resolved

jakobbotsch reviewed Mar 18, 2026

View reviewed changes

src/coreclr/jit/fgwasm.cpp Outdated Show resolved Hide resolved

jakobbotsch reviewed Mar 18, 2026

View reviewed changes

src/coreclr/jit/flowgraph.cpp Show resolved Hide resolved

jakobbotsch approved these changes Mar 18, 2026

View reviewed changes

AndyAyersMS added 3 commits March 18, 2026 09:26

make phases LIR only; simplify accordingly

f34a6e8

step blocks ensure continuation is in same handler region as the try

84d59aa

likewise we can simplify marking try regions as requiring runtime res…

ebe2f2b

…umption

Copilot AI review requested due to automatic review settings March 18, 2026 17:01

Copilot started reviewing on behalf of AndyAyersMS March 18, 2026 17:03 View session

Copilot AI reviewed Mar 18, 2026

View reviewed changes

src/coreclr/jit/emitwasm.cpp Show resolved Hide resolved

src/coreclr/jit/codegenwasm.cpp Show resolved Hide resolved

src/coreclr/jit/codegenwasm.cpp Show resolved Hide resolved

src/coreclr/jit/codegenwasm.cpp Show resolved Hide resolved

AndyAyersMS mentioned this pull request Mar 18, 2026

[Wasm RyuJIT] Basic Control Flow #121178

Open

jakobbotsch reviewed Mar 20, 2026

View reviewed changes

src/coreclr/jit/fgwasm.cpp Show resolved Hide resolved

jakobbotsch reviewed Mar 20, 2026

View reviewed changes

src/coreclr/jit/flowgraph.cpp Show resolved Hide resolved

jakobbotsch approved these changes Mar 20, 2026

View reviewed changes

AndyAyersMS merged commit 16c2ce3 into dotnet:main Mar 20, 2026
127 of 135 checks passed

dotnet-maestro bot mentioned this pull request Mar 21, 2026

[main] Source code updates from dotnet/runtime dotnet/dotnet#5588

Open

Conversation

AndyAyersMS commented Mar 16, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

Copilot AI left a comment

Choose a reason for hiding this comment

Pull request overview

Reviewed changes

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Copilot AI left a comment

Choose a reason for hiding this comment

Pull request overview

Reviewed changes

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

AndyAyersMS commented Mar 17, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

jakobbotsch commented Mar 17, 2026

Uh oh!

Copilot AI left a comment

Choose a reason for hiding this comment

Pull request overview

Reviewed changes

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

jakobbotsch left a comment

Choose a reason for hiding this comment

Uh oh!

Copilot AI left a comment

Choose a reason for hiding this comment

Pull request overview

Reviewed changes

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

jakobbotsch left a comment

Choose a reason for hiding this comment

Uh oh!

AndyAyersMS commented Mar 20, 2026

Uh oh!

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

4 participants

AndyAyersMS commented Mar 16, 2026 •

edited

Loading

AndyAyersMS commented Mar 17, 2026 •

edited

Loading