support methods with the VM backend
#775
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Summary ======= Enable dispatcher generation for the VM backend, which makes `method` (including multi-methods) available for the standalone VM target. Note that this doesn't apply to compile-time execution, where using `method`s is still unsupported. Details ======= * move the `chckNilDisp` compilerproc into the `system` module and replace the `== nil` with `isNil` (more on that later) * only report errors on method usage from `vmgne` when not in the `standalone` mode * generate the method dispatcher prior to generating code in `vmbackend` The VM code generator (`vmgen`) previously checked for whether a procedure returns something by testing for the presence of a procedure's `result` AST slot. For methods - where the AST always has a `result` slot, regardless of whether they have a return value - this test is no longer enough, and is replaced with inspecting the return type. Regarding the `== nil` -> `isNil` change: the VM comparison operator for pointer-like types (which `==` maps to) requires both operands to be of same dynamic type, but in `chckNilDisp`, this is not necessarily the case (for example, when the dispatched-through type is a `ref` type). The proper solution would be for `cgmeth.genDispatcher` to wrap the argument in a `cast[pointer]`, but the VM doesn't yet support casting references to pointers.
zerbina
added
enhancement
saem
approved these changes
Jun 27, 2023
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/merge |
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Merge requested by: @saem Contents after the first section break of the PR description has been removed and preserved below:
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Summary
Enable dispatcher generation for the VM backend, which makes
method(including multi-methods) available for the standalone VM target. Note
that this doesn't apply to compile-time execution, where using
methodsis still unsupported.
Details
chckNilDispcompilerproc into thesystemmodule andreplace the
== nilwithisNil(more on that later)vmgnewhen not in thestandalonemoderealTypeprocedure toroutineSignaturevmbackendmethodtests for the VM targetThe VM code generator (
vmgen) previously checked for whether aprocedure returns something by testing for the presence of a procedure's
resultAST slot. For methods - where the AST always has aresultslot, regardless of whether they have a return value - this test is
no longer enough, and is replaced with inspecting the return type.
Regarding the
== nil->isNilchange: the VM comparison operator forpointer-like types (which
==maps to) requires both operands to be ofsame dynamic type, but in
chckNilDisp, this is not necessarily thecase (for example, when the dispatched-through type is a
reftype).The proper solution would be for
cgmeth.genDispatcherto wrap theargument in a
cast[pointer], but the VM doesn't yet support castingreferences to pointers.