src/cmd/compile/internal/ssa/cache.go

// Copyright 2017 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 ssa

import (
	"cmd/internal/obj"
	"sort"
)

// A Cache holds reusable compiler state.
// It is intended to be re-used for multiple Func compilations.
type Cache struct {
	// Storage for low-numbered values and blocks.
	values [2000]Value
	blocks [200]Block
	locs   [2000]Location

	// Reusable stackAllocState.
	// See stackalloc.go's {new,put}StackAllocState.
	stackAllocState *stackAllocState

	domblockstore []ID         // scratch space for computing dominators
	scrSparseSet  []*sparseSet // scratch sparse sets to be re-used.
	scrSparseMap  []*sparseMap // scratch sparse maps to be re-used.
	scrPoset      []*poset     // scratch poset to be reused
	// deadcode contains reusable slices specifically for the deadcode pass.
	// It gets special treatment because of the frequency with which it is run.
	deadcode struct {
		liveOrderStmts []*Value
		live           []bool
		q              []*Value
	}
	// Reusable regalloc state.
	regallocValues []valState

	ValueToProgAfter []*obj.Prog
	debugState       debugState

	Liveness interface{} // *gc.livenessFuncCache
}

func (c *Cache) Reset() {
	nv := sort.Search(len(c.values), func(i int) bool { return c.values[i].ID == 0 })
	xv := c.values[:nv]
	for i := range xv {
		xv[i] = Value{}
	}
	nb := sort.Search(len(c.blocks), func(i int) bool { return c.blocks[i].ID == 0 })
	xb := c.blocks[:nb]
	for i := range xb {
		xb[i] = Block{}
	}
	nl := sort.Search(len(c.locs), func(i int) bool { return c.locs[i] == nil })
	xl := c.locs[:nl]
	for i := range xl {
		xl[i] = nil
	}

	// regalloc sets the length of c.regallocValues to whatever it may use,
	// so clear according to length.
	for i := range c.regallocValues {
		c.regallocValues[i] = valState{}
	}

	// liveOrderStmts gets used multiple times during compilation of a function.
	// We don't know where the high water mark was, so reslice to cap and search.
	c.deadcode.liveOrderStmts = c.deadcode.liveOrderStmts[:cap(c.deadcode.liveOrderStmts)]
	no := sort.Search(len(c.deadcode.liveOrderStmts), func(i int) bool { return c.deadcode.liveOrderStmts[i] == nil })
	xo := c.deadcode.liveOrderStmts[:no]
	for i := range xo {
		xo[i] = nil
	}
	c.deadcode.q = c.deadcode.q[:cap(c.deadcode.q)]
	nq := sort.Search(len(c.deadcode.q), func(i int) bool { return c.deadcode.q[i] == nil })
	xq := c.deadcode.q[:nq]
	for i := range xq {
		xq[i] = nil
	}
}