compiler: bound aggregate call signatures by jakebailey · Pull Request #5625 · tinygo-org/tinygo

jakebailey · 2026-08-29T00:28:06Z

This is a sort-of more involved alternative to #5618; the gist is that we ensure we limit everything to up to 1000 scalar elements across the board. Back when I did #5526, I had something like this, but scaled it back because I didn't think exactness would matter too much so long as we didn't overload LLVM. But, I guess it does matter.

Copilot

Pull request overview

This PR limits scalarized aggregate function signatures to 1,000 parameters.

Changes:

Selects aggregate parameters for indirect passing.
Handles calls, interfaces, defers, goroutines, and exported ABI validation.
Adds ABI and global-reference tests.

Reviewed changes

Copilot reviewed 15 out of 15 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
`builder/build.go`	Validates WebAssembly signatures.
`compiler/calls.go`	Centralizes ABI argument handling.
`compiler/compiler.go`	Applies ABI choices to calls and functions.
`compiler/compiler_test.go`	Tests aggregate ABI limits.
`compiler/defer.go`	Applies the ABI to deferred calls.
`compiler/func.go`	Calculates and validates function ABIs.
`compiler/goroutine.go`	Applies the ABI to goroutine arguments.
`compiler/interface.go`	Handles interface invoke wrappers.
`compiler/llvmutil/llvm.go`	Removes temporary global references.
`compiler/llvmutil/llvm_test.go`	Tests global-reference removal.
`compiler/symbol.go`	Protects indirect signatures during optimization.
`compiler/testdata/aggregate-abi.go`	Adds internal ABI fixtures.
`compiler/testdata/aggregate-export-abi.go`	Adds exported ABI fixtures.
`transform/interface-lowering.go`	Reports incompatible interface ABIs.
`transform/optimizer.go`	Removes temporary ABI roots.

Suppressed comments (2)

compiler/compiler.go:2326

This ABI calculation omits the synthetic typecode parameter that is appended below. At the 1000 parameter boundary, the invoke function spills an aggregate but this call passes it directly, which gives the callee a different ABI.

		abi = b.getInterfaceFunctionABI(instr.Signature())

compiler/interface.go:1350

This uses the concrete receiver when it selects indirect parameters. The interface invoke ABI replaces that receiver with a pointer, so it can select different nonreceiver parameters and the wrapper then forwards values with the wrong ABI.

	receiverType := abi.params[0].llvmType
	var expandedReceiverType []llvm.Type
	receiverIndirect := abi.params[0].indirect
	var receiverInfos []paramInfo
	if receiverIndirect {
		receiverInfos = []paramInfo{{llvmType: c.dataPtrType}}
	} else {
		receiverInfos = c.expandDirectFormalParamType(receiverType, "", nil)

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Copilot

Pull request overview

Copilot reviewed 15 out of 15 changed files in this pull request and generated no new comments.

Suppressed comments (1)

Previously missed (1) — in code that hasn't changed since the last review.

compiler/compiler_test.go:249

This test checks only that the compiler emits the marker. It does not run LowerInterfaces, so the new diagnostic path is not tested. Add a transform or build test that checks the expected error and a compatible exported interface call.

	if markedWrappers != 1 {

deadprogram · 2026-09-12T12:50:21Z

Thank you for this work @jakebailey. Here are the edited results from an automated review.

Findings

Dead code and stale text

compiler/func.go:198 - aggregateValueCount now has only one caller, compiler_test.go:505. No production code uses it.
compiler/calls.go:175 - the comment refers to expandFormalParamType, which this PR removes.

Unrelated behavior change

transform/optimizer.go - the second commit moves the config.Scheduler() == "none" goroutine check from before the ThinLTO pre-link pipeline to after it. Only RemoveGlobalReferences and the new globaldce must move. The check now runs after dead code elimination, so a goroutine start that the optimizer removes no longer reports attempted to start a goroutine without a scheduler. The commit message does not mention this. Is the move necessary?

Polish

transform/optimizer.go - the added globaldce runs on every build, also when no tinygo.indirect-abi global exists. A guard prevents the unnecessary pass.
transform/interface-lowering.go:279 - fmt.Errorf("%s", ...) gives an error with no source position. The other code in this pass uses errorAt. The loop also returns at the first error, so the user sees one diagnostic at a time.
compiler/compiler.go:1446 - SetInsertPointBefore in the phi loop leaves the insert point in a predecessor block after the loop ends. This is correct now, but it can break later changes.
The validation message function bigExport has more than 1000 WebAssembly parameters after ABI lowering does not tell the user that //export prevented the lowering, or what to change.

Process

The branch is 36 commits behind dev. Please rebase before merge.

jakebailey · 2026-09-12T13:49:53Z

Debased and updated, PTAL

Plan internal aggregate parameter lowering from each complete function signature. Count scalar leaves, the context parameter, and any hidden aggregate-result pointer, then pass the largest aggregates indirectly until the signature fits within the 1,000-parameter limit. This keeps the ABI policy target-independent and leaves fitting signatures unchanged. Preserve exported ABIs, validate final WebAssembly signatures that cannot be rewritten, release temporary roots before final dead-code elimination, and diagnose incompatible exported methods.

Include the interface typecode when budgeting invoke signatures and keep method parameter lowering consistent between concrete and interface calls. Preserve valid exported methods with large receivers. Materialize indirect aggregate phi inputs in their predecessor blocks, and retain temporary argument-promotion guards through the ThinLTO pre-link pipeline before final dead-code elimination.

dgryski · 2026-09-15T17:55:11Z

Passes my test corpus.

jakebailey requested a balanced review from Copilot August 29, 2026 00:28

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jakebailey commented Aug 29, 2026

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Comment thread builder/build.go

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Comment thread transform/optimizer.go Outdated

jakebailey requested a balanced review from Copilot August 29, 2026 01:00

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jakebailey marked this pull request as ready for review August 29, 2026 16:07

jakebailey mentioned this pull request Aug 29, 2026

wasm: struct-by-value parameters scalarize into >1000-param function types, rejected by browsers and wasm-tools #5615

Open

jakebailey requested review from deadprogram and dgryski September 11, 2026 14:36

jakebailey force-pushed the fix/aggregate-lowering branch from 8af9cfd to 04564c7 Compare September 12, 2026 13:42

jakebailey added 2 commits September 15, 2026 07:53

jakebailey force-pushed the fix/aggregate-lowering branch from 04564c7 to 4637038 Compare September 15, 2026 14:53

dgryski mentioned this pull request Sep 15, 2026

compiler: pass large aggregate parameters indirectly (#5615) #5618

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compiler: bound aggregate call signatures - #5625

compiler: bound aggregate call signatures#5625
jakebailey wants to merge 2 commits into
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jakebailey:fix/aggregate-lowering

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deadprogram commented Sep 12, 2026

Findings

Dead code and stale text

Unrelated behavior change

Polish

Process

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jakebailey commented Sep 12, 2026

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dgryski commented Sep 15, 2026

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