Effect analysis for indirect call expressions by stevenfontanella · Pull Request #8625 · WebAssembly/binaryen

stevenfontanella · 2026-04-19T08:51:38Z

Part of #8615. After #8609, we compute effects for indirect call expressions, but only reflect this in the call-site via the effects of the Function that contains the indirect call. That let us reason about effects only one layer of indirection away, for example in the following module:

(func $a
  (call_ref $t (...))
)

(func $b
  (call $a)
)

If we know that an indirect call to $t can't possibly have any effects (e.g. its only potential target is a nop), we'd be able to optimize away (call $a) but not the (call_ref) itself, since the effects only got stored in the effects of $a.

This PR lets us reason about indirect call effects at the expression level within function bodies by adding a map from HeapType to effects typeEffects in wasm::Module. As a result we can completely optimize out the call_ref in the above example.

Drive-by fixes:

Set an unconditional trap effect on call_indirect when the call type doesn't match the target table.
Correctly set branchesOut for return_call on call.without.effects. Previously this would not have a branchesOut effect which may have allowed incorrect reorderings (we shouldn't move an effectful expression above a return_call but we would have allowed this). Will follow up in return_call with call.without.effects optimizes incorrectly #8693.

stevenfontanella · 2026-04-23T23:17:06Z

Seems like JJ + Github don't play well when I'm on a branch based on another branch that had a merge commit. Will fix this after merging the other branch.

When running in --closed-world, compute effects for indirect calls by unioning the effects of all potential functions of that type. In --closed-world, we assume that all references originate in our module, so the only possible functions that we don't know about are imports. Previously [we gave up on effects analysis](https://github.com/WebAssembly/binaryen/blob/29b2d42e8a748fbe1095696d58a52b7bf83e2253/src/passes/GlobalEffects.cpp#L83-L87) for indirect calls. Yields a very small byte count reduction in calcworker (3799354 - 3799297 = 57 bytes). Also shows no significant difference in Binaryen runtime: (0.1346069 -> 0.13375045 = <1% improvement, probably within noise). We expect more benefits after we're able to share indirect call effects with other passes, since currently they're only seen one layer up for callers of functions that indirectly call functions (see the newly-added tests for examples). Followups: * Share effect information per type with other passes besides just via Function::effects (#8625) * Exclude functions that don't have an address (i.e. functions that aren't the target of ref.func) from effect analysis () * Compute effects more precisely for exact + nullable/non-nullable references Part of #8615.

Gemini WIP Try changing call effects

stevenfontanella · 2026-05-15T19:28:48Z

Will run the fuzzer for a few hours.

stevenfontanella · 2026-05-15T22:06:22Z

Ran 3900 iterations with no issues.

kripken · 2026-05-18T22:42:46Z

+  // When types are rewritten globally, the target type inherits the effects of
+  // source type (see type-updating.cpp). If the type of just one function is
+  // rewritten, we don't update this, because such a rewrite is only valid
+  // if the function is not the target of an indirect call (otherwise the
+  // indirect call would have to be rewritten too).


I don't understand the second paragraph here.

It sounds like it might be an optimization (we save an update we don't need) - if so, it doesn't need to be in the header. But it sounds like it also might be an invariant, in which case I am confused?

stevenfontanella · 2026-05-19T00:12:21Z

(Sorry for the force-push, I thought it would be fine to force-push changes to the latest commit that hasn't been looked at yet, but it seems that that still messed with the comment history)

kripken · 2026-05-19T16:41:56Z

Hmm, yeah, the force-push is making it hard to read the diff here. This is all I see from github's "compare changes" button, one comment changed:

https://github.com/WebAssembly/binaryen/compare/70194ce48cae852404641f5af1ad5320cd918d72..038480b8103aeb4f91a8c9d783480a9a3217d740

Not shown there is your new comment with Also, we can filter out throws for return calls because they are, which looks good, thanks.

Were there other changes?

(In general I always recommend not force-pushing, but this is something I've had no success in convincing anyone about 😄 )

aheejin · 2026-05-19T17:01:34Z

(In general I always recommend not force-pushing, but this is something I've had no success in convincing anyone about 😄 )

I have been endorsing this too. You can see changes with the "Compare" button, AFAIK it only compares one commit; when several changes have been pushed since you last reviewed a PR, Github doesn't show them as aggregate changes. (And worse if one of them is a force-push)

kripken

Some testing comments (but I haven't read them all yet).

kripken

Nice!

Thanks for your patience with my comments.

kripken · 2026-05-21T22:40:56Z

+;; RUN: foreach %s %t wasm-opt -all --closed-world --ignore-implicit-traps --generate-global-effects --vacuum -S -o - | filecheck %s
+
+;; Tests for aggregating effects from indirect calls in GlobalEffects when
+;; --closed-world is true. Continued from global-effects-closed-world.wast.


Suggested change

;; --closed-world is true. Continued from global-effects-closed-world.wast.

;; --closed-world is true. Continued from global-effects-closed-world.wast,

;; but adding --ignore-implicit-traps.

stevenfontanella force-pushed the expression-effects branch from 690ee8d to 75481a7 Compare April 19, 2026 08:56

tlively reviewed Apr 20, 2026

View reviewed changes

Comment thread src/ir/effects.h Outdated

stevenfontanella force-pushed the indirect-effects-scc branch from 189d543 to 2630eff Compare April 21, 2026 20:15

stevenfontanella mentioned this pull request Apr 23, 2026

Compute effects for indirect calls in GlobalEffects #8609

Merged

stevenfontanella force-pushed the expression-effects branch from 75481a7 to 36a4fb5 Compare April 23, 2026 23:07

Base automatically changed from indirect-effects-scc to main April 24, 2026 21:36

stevenfontanella force-pushed the expression-effects branch from 36a4fb5 to e65a243 Compare April 24, 2026 22:16

stevenfontanella added 2 commits May 6, 2026 18:05

Use effects for indirect call expressions

58eb5c2

PR updates

253c092

stevenfontanella force-pushed the expression-effects branch 3 times, most recently from 30a31e1 to 60665f3 Compare May 7, 2026 20:33

WIP

2156d99

Gemini WIP Try changing call effects

stevenfontanella force-pushed the expression-effects branch from 60665f3 to 2156d99 Compare May 7, 2026 20:44

stevenfontanella marked this pull request as ready for review May 7, 2026 21:33

stevenfontanella requested a review from a team as a code owner May 7, 2026 21:33

stevenfontanella requested review from aheejin and removed request for a team May 7, 2026 21:33

aheejin reviewed May 12, 2026

View reviewed changes

Comment thread test/lit/passes/global-effects-closed-world-tnh.wast Outdated

Comment thread test/lit/passes/global-effects-closed-world.wast

Comment thread src/ir/effects.h Outdated

Comment thread src/ir/effects.h

stevenfontanella added 2 commits May 12, 2026 16:29

PR updates

7facc2a

Extract a common function for setting effects for function calls

5aac82a

kripken reviewed May 12, 2026

View reviewed changes

Comment thread src/ir/effects.h Outdated

Extract out fix for future PR

63d5515

stevenfontanella requested a review from aheejin May 12, 2026 20:45

kripken reviewed May 12, 2026

View reviewed changes

Comment thread src/ir/effects.h Outdated

Comment thread src/ir/effects.h

Comment thread src/wasm.h Outdated

kripken reviewed May 12, 2026

View reviewed changes

Comment thread src/ir/effects.h Outdated

Comment thread src/ir/effects.h

Comment thread src/ir/effects.h

Comment thread src/support/utilities.h Outdated

Comment thread src/ir/effects.h

aheejin reviewed May 12, 2026

View reviewed changes

Comment thread src/ir/effects.h Outdated

Comment thread src/ir/effects.h Outdated

stevenfontanella mentioned this pull request May 13, 2026

Account for unaddressed funcs in GlobalEffects #8644

Open

kripken reviewed May 14, 2026

View reviewed changes

Comment thread src/ir/effects.h Outdated

kripken reviewed May 14, 2026

View reviewed changes

Comment thread src/ir/effects.h

PR updates

979db05

stevenfontanella force-pushed the expression-effects branch from 7eed45c to 979db05 Compare May 15, 2026 04:19

Bring back trap logic for call_indirect

cae5353

stevenfontanella requested review from aheejin and kripken May 18, 2026 18:08

kripken reviewed May 18, 2026

View reviewed changes

PR updates

038480b

stevenfontanella force-pushed the expression-effects branch from 70194ce to 038480b Compare May 19, 2026 00:08

Add deduction guide to fix build on macos 14 after #8721

acb16ad

Rename bodyEffects -> callTargetEffects

4633c60

kripken reviewed May 19, 2026

View reviewed changes

Comment thread src/wasm.h Outdated

aheejin reviewed May 19, 2026

View reviewed changes

Comment thread src/ir/effects.h Outdated

stevenfontanella added 2 commits May 20, 2026 18:26

Rename and update comment

1d75c25

Remove unneeded/incorrect TODO

ae3235e

kripken reviewed May 20, 2026

View reviewed changes

Comment thread src/wasm.h

aheejin mentioned this pull request May 21, 2026

[Fuzzer] Make Split's exports a list of strings #8731

Merged

Fix unneeded copies of EffectAnalyzer

bdc4533

stevenfontanella changed the title ~~Use effects for indirect call expressions~~ Effect analysis for indirect call expressions May 21, 2026

kripken reviewed May 21, 2026

View reviewed changes

stevenfontanella added 3 commits May 21, 2026 17:13

Add comments about shared_ptr

cc7b76d

Comment updates

ea627e5

Give calls to uninhabited types trap effect

653aa22

kripken approved these changes May 21, 2026

View reviewed changes

	;; --closed-world is true. Continued from global-effects-closed-world.wast.
	;; --closed-world is true. Continued from global-effects-closed-world.wast,
	;; but adding --ignore-implicit-traps.

Conversation

stevenfontanella commented Apr 19, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

Uh oh!

stevenfontanella commented Apr 23, 2026

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

stevenfontanella commented May 15, 2026

Uh oh!

stevenfontanella commented May 15, 2026

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

kripken May 18, 2026

Choose a reason for hiding this comment

Uh oh!

stevenfontanella commented May 19, 2026

Uh oh!

kripken commented May 19, 2026

Uh oh!

aheejin commented May 19, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

kripken left a comment

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

kripken left a comment

Choose a reason for hiding this comment

Uh oh!

kripken May 21, 2026

Choose a reason for hiding this comment

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

4 participants

stevenfontanella commented Apr 19, 2026 •

edited

Loading

aheejin commented May 19, 2026 •

edited

Loading