src/cmd/compile/internal/gc/compile.go

// Copyright 2011 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package gc

import (
	"cmp"
	"internal/race"
	"math/rand"
	"slices"
	"sync"

	"cmd/compile/internal/base"
	"cmd/compile/internal/ir"
	"cmd/compile/internal/liveness"
	"cmd/compile/internal/objw"
	"cmd/compile/internal/pgoir"
	"cmd/compile/internal/ssagen"
	"cmd/compile/internal/staticinit"
	"cmd/compile/internal/types"
	"cmd/compile/internal/walk"
	"cmd/internal/obj"
)

// "Portable" code generation.

var (
	compilequeue []*ir.Func // functions waiting to be compiled
)

func enqueueFunc(fn *ir.Func, symABIs *ssagen.SymABIs) {
	if ir.CurFunc != nil {
		base.FatalfAt(fn.Pos(), "enqueueFunc %v inside %v", fn, ir.CurFunc)
	}

	if ir.FuncName(fn) == "_" {
		// Skip compiling blank functions.
		// Frontend already reported any spec-mandated errors (#29870).
		return
	}

	if fn.IsClosure() {
		return // we'll get this as part of its enclosing function
	}

	if ssagen.CreateWasmImportWrapper(fn) {
		return
	}

	if len(fn.Body) == 0 {
		if ir.IsIntrinsicSym(fn.Sym()) && fn.Sym().Linkname == "" && !symABIs.HasDef(fn.Sym()) {
			// Generate the function body for a bodyless intrinsic, in case it
			// is used in a non-call context (e.g. as a function pointer).
			// We skip functions defined in assembly, or has a linkname (which
			// could be defined in another package).
			ssagen.GenIntrinsicBody(fn)
		} else {
			// Initialize ABI wrappers if necessary.
			ir.InitLSym(fn, false)
			types.CalcSize(fn.Type())
			a := ssagen.AbiForBodylessFuncStackMap(fn)
			abiInfo := a.ABIAnalyzeFuncType(fn.Type()) // abiInfo has spill/home locations for wrapper
			if fn.ABI == obj.ABI0 {
				// The current args_stackmap generation assumes the function
				// is ABI0, and only ABI0 assembly function can have a FUNCDATA
				// reference to args_stackmap (see cmd/internal/obj/plist.go:Flushplist).
				// So avoid introducing an args_stackmap if the func is not ABI0.
				liveness.WriteFuncMap(fn, abiInfo)

				x := ssagen.EmitArgInfo(fn, abiInfo)
				objw.Global(x, int32(len(x.P)), obj.RODATA|obj.LOCAL)
			}
			return
		}
	}

	errorsBefore := base.Errors()

	todo := []*ir.Func{fn}
	for len(todo) > 0 {
		next := todo[len(todo)-1]
		todo = todo[:len(todo)-1]

		prepareFunc(next)
		todo = append(todo, next.Closures...)
	}

	if base.Errors() > errorsBefore {
		return
	}

	// Enqueue just fn itself. compileFunctions will handle
	// scheduling compilation of its closures after it's done.
	compilequeue = append(compilequeue, fn)
}

// prepareFunc handles any remaining frontend compilation tasks that
// aren't yet safe to perform concurrently.
func prepareFunc(fn *ir.Func) {
	// Set up the function's LSym early to avoid data races with the assemblers.
	// Do this before walk, as walk needs the LSym to set attributes/relocations
	// (e.g. in MarkTypeUsedInInterface).
	ir.InitLSym(fn, true)

	// If this function is a compiler-generated outlined global map
	// initializer function, register its LSym for later processing.
	if staticinit.MapInitToVar != nil {
		if _, ok := staticinit.MapInitToVar[fn]; ok {
			ssagen.RegisterMapInitLsym(fn.Linksym())
		}
	}

	// Calculate parameter offsets.
	types.CalcSize(fn.Type())

	// Generate wrappers between Go ABI and Wasm ABI, for a wasmexport
	// function.
	// Must be done after InitLSym and CalcSize.
	ssagen.GenWasmExportWrapper(fn)

	ir.CurFunc = fn
	walk.Walk(fn)
	if ir.MatchAstDump(fn, "walk") {
		ir.AstDump(fn, "walk, "+ir.FuncName(fn))
	}
	ir.CurFunc = nil // enforce no further uses of CurFunc

	base.Ctxt.DwTextCount++
}

// compileFunctions compiles all functions in compilequeue.
// It fans out nBackendWorkers to do the work
// and waits for them to complete.
func compileFunctions(profile *pgoir.Profile) {
	if race.Enabled {
		// Randomize compilation order to try to shake out races.
		tmp := make([]*ir.Func, len(compilequeue))
		perm := rand.Perm(len(compilequeue))
		for i, v := range perm {
			tmp[v] = compilequeue[i]
		}
		copy(compilequeue, tmp)
	} else {
		// Compile the longest functions first,
		// since they're most likely to be the slowest.
		// This helps avoid stragglers.
		// Since we remove from the end of the slice queue,
		// that means shortest to longest.
		slices.SortFunc(compilequeue, func(a, b *ir.Func) int {
			return cmp.Compare(len(a.Body), len(b.Body))
		})
	}

	var mu sync.Mutex
	var wg sync.WaitGroup
	mu.Lock()

	for workerId := range base.Flag.LowerC {
		// TODO: replace with wg.Go when the oldest bootstrap has it.
		// With the current policy, that'd be go1.27.
		wg.Add(1)
		go func() {
			defer wg.Done()
			var closures []*ir.Func
			for {
				mu.Lock()
				compilequeue = append(compilequeue, closures...)
				remaining := len(compilequeue)
				if remaining == 0 {
					mu.Unlock()
					return
				}
				fn := compilequeue[len(compilequeue)-1]
				compilequeue = compilequeue[:len(compilequeue)-1]
				mu.Unlock()
				ssagen.Compile(fn, workerId, profile)
				closures = fn.Closures
			}
		}()
	}

	types.CalcSizeDisabled = true // not safe to calculate sizes concurrently
	base.Ctxt.InParallel = true

	mu.Unlock()
	wg.Wait()
	compilequeue = nil

	base.Ctxt.InParallel = false
	types.CalcSizeDisabled = false
}