optimiser: transform calls to imported functions also when optimisation is disabled

[melsman]

No description provided.

[Copilot]

Pull request overview

Updates the Lambda optimiser pipeline so that argument-transformation/flattening of calls to imported (already-transformed) functions still happens even when optimisation is disabled (-no_opt / noopt). This prevents mismatches between call sites and imported function calling conventions in “no optimisation” builds.

Changes:

• Extend FixFlatten.flatten to also rewrite CHECK_REML nodes when a referenced lvar has a FIXphi transformation.
• When optimise_p() is false, run a “noopt” flattening pass (FixFlatten.flattening_noopt) instead of returning the input lambda unchanged.
• Add a regression test (stringconcat.sml) executed with noopt.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
src/Compiler/Lambda/OptLambda.sml	Runs flattening even with optimiser disabled; updates flatten traversal for CHECK_REML.
test/all.tst	Documents noopt and runs the new regression test with optimisation disabled.
test/stringconcat.sml	New regression program to exercise imported-function call transformation under noopt.
test/stringconcat.sml.out.ok	Expected output for the new regression test.

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[Copilot]

The token name for disabling the optimiser is updated to noopt here, but other .tst files still document nooptimiser (e.g. test/parallelism/all.tst). To avoid confusion for contributors and to keep the test-suite documentation consistent, update those headers too (or make the tester accept nooptimiser as an alias if that’s intended).