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[dev.typeparams] cmd/compile: add documentation for unified IR pipeline
While at it, also rename "useUnifiedIR" to "unified", to be consistent with "-d=unified" and "GOEXPERIMENT=unified". Change-Id: I48ffdb4b36368343893b74f174608f5f59278249 Reviewed-on: https://go-review.googlesource.com/c/go/+/328989 Trust: Cuong Manh Le <cuong.manhle.vn@gmail.com> Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com> TryBot-Result: Go Bot <gobot@golang.org> Reviewed-by: Matthew Dempsky <mdempsky@google.com>
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@ -77,7 +77,7 @@ func LoadPackage(filenames []string) {
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base.Timer.AddEvent(int64(lines), "lines")
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base.Timer.AddEvent(int64(lines), "lines")
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if base.Debug.Unified != 0 {
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if base.Debug.Unified != 0 {
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useUnifiedIR(noders)
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unified(noders)
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return
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return
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}
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}
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@ -20,7 +20,7 @@ import (
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// -cmp when compared against the legacy frontend behavior, but can be
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// -cmp when compared against the legacy frontend behavior, but can be
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// removed after that's no longer a concern.
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// removed after that's no longer a concern.
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// quirksMode controls whether behavior specific to satsifying
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// quirksMode controls whether behavior specific to satisfying
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// toolstash -cmp is used.
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// toolstash -cmp is used.
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func quirksMode() bool {
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func quirksMode() bool {
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// Currently, unified IR doesn't try to be compatible with
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// Currently, unified IR doesn't try to be compatible with
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@ -28,9 +28,48 @@ import (
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// later.
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// later.
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var localPkgReader *pkgReader
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var localPkgReader *pkgReader
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// useUnifiedIR reports whether the unified IR frontend should be
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// unified construct the local package's IR from syntax's AST.
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// used; and if so, uses it to construct the local package's IR.
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//
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func useUnifiedIR(noders []*noder) {
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// The pipeline contains 2 steps:
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//
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// (1) Generate package export data "stub".
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//
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// (2) Generate package IR from package export data.
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//
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// The package data "stub" at step (1) contains everything from the local package,
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// but nothing that have been imported. When we're actually writing out export data
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// to the output files (see writeNewExport function), we run the "linker", which does
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// a few things:
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//
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// + Updates compiler extensions data (e.g., inlining cost, escape analysis results).
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//
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// + Handles re-exporting any transitive dependencies.
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//
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// + Prunes out any unnecessary details (e.g., non-inlineable functions, because any
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// downstream importers only care about inlinable functions).
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//
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// The source files are typechecked twice, once before writing export data
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// using types2 checker, once after read export data using gc/typecheck.
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// This duplication of work will go away once we always use types2 checker,
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// we can remove the gc/typecheck pass. The reason it is still here:
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//
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// + It reduces engineering costs in maintaining a fork of typecheck
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// (e.g., no need to backport fixes like CL 327651).
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//
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// + It makes it easier to pass toolstash -cmp.
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//
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// + Historically, we would always re-run the typechecker after import, even though
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// we know the imported data is valid. It's not ideal, but also not causing any
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// problem either.
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//
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// + There's still transformation that being done during gc/typecheck, like rewriting
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// multi-valued function call, or transform ir.OINDEX -> ir.OINDEXMAP.
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//
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// Using syntax+types2 tree, which already has a complete representation of generics,
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// the unified IR has the full typed AST for doing introspection during step (1).
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// In other words, we have all necessary information to build the generic IR form
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// (see writer.captureVars for an example).
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func unified(noders []*noder) {
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inline.NewInline = InlineCall
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inline.NewInline = InlineCall
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if !quirksMode() {
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if !quirksMode() {
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@ -111,8 +150,9 @@ func useUnifiedIR(noders []*noder) {
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base.ExitIfErrors() // just in case
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base.ExitIfErrors() // just in case
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}
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}
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// writePkgStub type checks the given parsed source files and then
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// writePkgStub type checks the given parsed source files,
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// returns
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// writes an export data package stub representing them,
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// and returns the result.
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func writePkgStub(noders []*noder) string {
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func writePkgStub(noders []*noder) string {
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m, pkg, info := checkFiles(noders)
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m, pkg, info := checkFiles(noders)
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