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📁 ..
📄 README.md(8.14 KB)
📄 TODO(950 B)
📄 addressingmodes.go(23.64 KB)
📄 bench_test.go(531 B)
📄 biasedsparsemap.go(2.71 KB)
📄 block.go(11.1 KB)
📄 branchelim.go(11.98 KB)
📄 branchelim_test.go(5.21 KB)
📄 cache.go(2.46 KB)
📄 check.go(16.59 KB)
📄 checkbce.go(956 B)
📄 compile.go(18.19 KB)
📄 config.go(11.7 KB)
📄 copyelim.go(1.83 KB)
📄 copyelim_test.go(1.29 KB)
📄 critical.go(3.19 KB)
📄 cse.go(9.43 KB)
📄 cse_test.go(4.25 KB)
📄 deadcode.go(9.61 KB)
📄 deadcode_test.go(3.49 KB)
📄 deadstore.go(9.08 KB)
📄 deadstore_test.go(4.09 KB)
📄 debug.go(56.34 KB)
📄 debug_lines_test.go(8.29 KB)
📄 debug_test.go(28.75 KB)
📄 decompose.go(13.41 KB)
📄 dom.go(7.98 KB)
📄 dom_test.go(13.34 KB)
📄 expand_calls.go(63.5 KB)
📄 export_test.go(3.23 KB)
📄 flagalloc.go(6.68 KB)
📄 flags_amd64_test.s(533 B)
📄 flags_arm64_test.s(699 B)
📄 flags_test.go(2.49 KB)
📄 func.go(27.08 KB)
📄 func_test.go(13.07 KB)
📄 fuse.go(6.5 KB)
📄 fuse_branchredirect.go(3.24 KB)
📄 fuse_comparisons.go(4.04 KB)
📄 fuse_test.go(7.21 KB)
📁 gen
📄 html.go(34.72 KB)
📄 id.go(576 B)
📄 layout.go(4.82 KB)
📄 lca.go(3.77 KB)
📄 lca_test.go(1.65 KB)
📄 likelyadjust.go(15.24 KB)
📄 location.go(3.06 KB)
📄 loopbce.go(10.54 KB)
📄 loopreschedchecks.go(15.86 KB)
📄 looprotate.go(2.61 KB)
📄 lower.go(1.36 KB)
📄 magic.go(15.77 KB)
📄 magic_test.go(9.1 KB)
📄 nilcheck.go(11.06 KB)
📄 nilcheck_test.go(12.17 KB)
📄 numberlines.go(7.83 KB)
📄 op.go(18.65 KB)
📄 opGen.go(1.01 MB)
📄 opt.go(308 B)
📄 passbm_test.go(3.14 KB)
📄 phielim.go(1.48 KB)
📄 phiopt.go(8.08 KB)
📄 poset.go(37.2 KB)
📄 poset_test.go(18.14 KB)
📄 print.go(3.85 KB)
📄 prove.go(41.82 KB)
📄 regalloc.go(83.69 KB)
📄 regalloc_test.go(6.49 KB)
📄 rewrite.go(53.49 KB)
📄 rewrite386.go(289.01 KB)
📄 rewrite386splitload.go(4.05 KB)
📄 rewriteAMD64.go(888.95 KB)
📄 rewriteAMD64splitload.go(21.41 KB)
📄 rewriteARM.go(487.7 KB)
📄 rewriteARM64.go(751.84 KB)
📄 rewriteCond_test.go(10.62 KB)
📄 rewriteLOONG64.go(193.44 KB)
📄 rewriteMIPS.go(174.44 KB)
📄 rewriteMIPS64.go(195.55 KB)
📄 rewritePPC64.go(431.6 KB)
📄 rewriteRISCV64.go(159.66 KB)
📄 rewriteS390X.go(433.4 KB)
📄 rewriteWasm.go(109.86 KB)
📄 rewrite_test.go(6.91 KB)
📄 rewritedec.go(10.16 KB)
📄 rewritedec64.go(63.77 KB)
📄 rewritegeneric.go(617.96 KB)
📄 schedule.go(18.23 KB)
📄 schedule_test.go(2.91 KB)
📄 shift_test.go(4.05 KB)
📄 shortcircuit.go(12.63 KB)
📄 shortcircuit_test.go(1.31 KB)
📄 sizeof_test.go(855 B)
📄 softfloat.go(1.99 KB)
📄 sparsemap.go(1.98 KB)
📄 sparseset.go(1.54 KB)
📄 sparsetree.go(8.05 KB)
📄 stackalloc.go(12.79 KB)
📄 stackframe.go(290 B)
📄 stmtlines_test.go(2.96 KB)
📁 testdata
📄 tighten.go(4.3 KB)
📄 trim.go(4.24 KB)
📄 tuple.go(1.97 KB)
📄 value.go(15.21 KB)
📄 writebarrier.go(19.29 KB)
📄 writebarrier_test.go(1.75 KB)
📄 xposmap.go(3.29 KB)
📄 zcse.go(2.07 KB)
📄 zeroextension_test.go(1.66 KB)

Editing: cse.go

// Copyright 2015 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/compile/internal/types"
	"cmd/internal/src"
	"fmt"
	"sort"
)

// cse does common-subexpression elimination on the Function.
// Values are just relinked, nothing is deleted. A subsequent deadcode
// pass is required to actually remove duplicate expressions.
func cse(f *Func) {
	// Two values are equivalent if they satisfy the following definition:
	// equivalent(v, w):
	//   v.op == w.op
	//   v.type == w.type
	//   v.aux == w.aux
	//   v.auxint == w.auxint
	//   len(v.args) == len(w.args)
	//   v.block == w.block if v.op == OpPhi
	//   equivalent(v.args[i], w.args[i]) for i in 0..len(v.args)-1

// The algorithm searches for a partition of f's values into
	// equivalence classes using the above definition.
	// It starts with a coarse partition and iteratively refines it
	// until it reaches a fixed point.

// Make initial coarse partitions by using a subset of the conditions above.
	a := make([]*Value, 0, f.NumValues())
	if f.auxmap == nil {
		f.auxmap = auxmap{}
	}
	for _, b := range f.Blocks {
		for _, v := range b.Values {
			if v.Type.IsMemory() {
				continue // memory values can never cse
			}
			if f.auxmap[v.Aux] == 0 {
				f.auxmap[v.Aux] = int32(len(f.auxmap)) + 1
			}
			a = append(a, v)
		}
	}
	partition := partitionValues(a, f.auxmap)

// map from value id back to eqclass id
	valueEqClass := make([]ID, f.NumValues())
	for _, b := range f.Blocks {
		for _, v := range b.Values {
			// Use negative equivalence class #s for unique values.
			valueEqClass[v.ID] = -v.ID
		}
	}
	var pNum ID = 1
	for _, e := range partition {
		if f.pass.debug > 1 && len(e) > 500 {
			fmt.Printf("CSE.large partition (%d): ", len(e))
			for j := 0; j < 3; j++ {
				fmt.Printf("%s ", e[j].LongString())
			}
			fmt.Println()
		}

for _, v := range e {
			valueEqClass[v.ID] = pNum
		}
		if f.pass.debug > 2 && len(e) > 1 {
			fmt.Printf("CSE.partition #%d:", pNum)
			for _, v := range e {
				fmt.Printf(" %s", v.String())
			}
			fmt.Printf("\n")
		}
		pNum++
	}

// Split equivalence classes at points where they have
	// non-equivalent arguments.  Repeat until we can't find any
	// more splits.
	var splitPoints []int
	byArgClass := new(partitionByArgClass) // reusable partitionByArgClass to reduce allocations
	for {
		changed := false

// partition can grow in the loop. By not using a range loop here,
		// we process new additions as they arrive, avoiding O(n^2) behavior.
		for i := 0; i < len(partition); i++ {
			e := partition[i]

if opcodeTable[e[0].Op].commutative {
				// Order the first two args before comparison.
				for _, v := range e {
					if valueEqClass[v.Args[0].ID] > valueEqClass[v.Args[1].ID] {
						v.Args[0], v.Args[1] = v.Args[1], v.Args[0]
					}
				}
			}

// Sort by eq class of arguments.
			byArgClass.a = e
			byArgClass.eqClass = valueEqClass
			sort.Sort(byArgClass)

// Find split points.
			splitPoints = append(splitPoints[:0], 0)
			for j := 1; j < len(e); j++ {
				v, w := e[j-1], e[j]
				// Note: commutative args already correctly ordered by byArgClass.
				eqArgs := true
				for k, a := range v.Args {
					b := w.Args[k]
					if valueEqClass[a.ID] != valueEqClass[b.ID] {
						eqArgs = false
						break
					}
				}
				if !eqArgs {
					splitPoints = append(splitPoints, j)
				}
			}
			if len(splitPoints) == 1 {
				continue // no splits, leave equivalence class alone.
			}

// Move another equivalence class down in place of e.
			partition[i] = partition[len(partition)-1]
			partition = partition[:len(partition)-1]
			i--

// Add new equivalence classes for the parts of e we found.
			splitPoints = append(splitPoints, len(e))
			for j := 0; j < len(splitPoints)-1; j++ {
				f := e[splitPoints[j]:splitPoints[j+1]]
				if len(f) == 1 {
					// Don't add singletons.
					valueEqClass[f[0].ID] = -f[0].ID
					continue
				}
				for _, v := range f {
					valueEqClass[v.ID] = pNum
				}
				pNum++
				partition = append(partition, f)
			}
			changed = true
		}

if !changed {
			break
		}
	}

sdom := f.Sdom()

// Compute substitutions we would like to do. We substitute v for w
	// if v and w are in the same equivalence class and v dominates w.
	rewrite := make([]*Value, f.NumValues())
	byDom := new(partitionByDom) // reusable partitionByDom to reduce allocs
	for _, e := range partition {
		byDom.a = e
		byDom.sdom = sdom
		sort.Sort(byDom)
		for i := 0; i < len(e)-1; i++ {
			// e is sorted by domorder, so a maximal dominant element is first in the slice
			v := e[i]
			if v == nil {
				continue
			}

e[i] = nil
			// Replace all elements of e which v dominates
			for j := i + 1; j < len(e); j++ {
				w := e[j]
				if w == nil {
					continue
				}
				if sdom.IsAncestorEq(v.Block, w.Block) {
					rewrite[w.ID] = v
					e[j] = nil
				} else {
					// e is sorted by domorder, so v.Block doesn't dominate any subsequent blocks in e
					break
				}
			}
		}
	}

rewrites := int64(0)

// Apply substitutions
	for _, b := range f.Blocks {
		for _, v := range b.Values {
			for i, w := range v.Args {
				if x := rewrite[w.ID]; x != nil {
					if w.Pos.IsStmt() == src.PosIsStmt {
						// about to lose a statement marker, w
						// w is an input to v; if they're in the same block
						// and the same line, v is a good-enough new statement boundary.
						if w.Block == v.Block && w.Pos.Line() == v.Pos.Line() {
							v.Pos = v.Pos.WithIsStmt()
							w.Pos = w.Pos.WithNotStmt()
						} // TODO and if this fails?
					}
					v.SetArg(i, x)
					rewrites++
				}
			}
		}
		for i, v := range b.ControlValues() {
			if x := rewrite[v.ID]; x != nil {
				if v.Op == OpNilCheck {
					// nilcheck pass will remove the nil checks and log
					// them appropriately, so don't mess with them here.
					continue
				}
				b.ReplaceControl(i, x)
			}
		}
	}

if f.pass.stats > 0 {
		f.LogStat("CSE REWRITES", rewrites)
	}
}

// An eqclass approximates an equivalence class. During the
// algorithm it may represent the union of several of the
// final equivalence classes.
type eqclass []*Value

// partitionValues partitions the values into equivalence classes
// based on having all the following features match:
//   - opcode
//   - type
//   - auxint
//   - aux
//   - nargs
//   - block # if a phi op
//   - first two arg's opcodes and auxint
//   - NOT first two arg's aux; that can break CSE.
//
// partitionValues returns a list of equivalence classes, each
// being a sorted by ID list of *Values. The eqclass slices are
// backed by the same storage as the input slice.
// Equivalence classes of size 1 are ignored.
func partitionValues(a []*Value, auxIDs auxmap) []eqclass {
	sort.Sort(sortvalues{a, auxIDs})

var partition []eqclass
	for len(a) > 0 {
		v := a[0]
		j := 1
		for ; j < len(a); j++ {
			w := a[j]
			if cmpVal(v, w, auxIDs) != types.CMPeq {
				break
			}
		}
		if j > 1 {
			partition = append(partition, a[:j])
		}
		a = a[j:]
	}

return partition
}
func lt2Cmp(isLt bool) types.Cmp {
	if isLt {
		return types.CMPlt
	}
	return types.CMPgt
}

type auxmap map[Aux]int32

func cmpVal(v, w *Value, auxIDs auxmap) types.Cmp {
	// Try to order these comparison by cost (cheaper first)
	if v.Op != w.Op {
		return lt2Cmp(v.Op < w.Op)
	}
	if v.AuxInt != w.AuxInt {
		return lt2Cmp(v.AuxInt < w.AuxInt)
	}
	if len(v.Args) != len(w.Args) {
		return lt2Cmp(len(v.Args) < len(w.Args))
	}
	if v.Op == OpPhi && v.Block != w.Block {
		return lt2Cmp(v.Block.ID < w.Block.ID)
	}
	if v.Type.IsMemory() {
		// We will never be able to CSE two values
		// that generate memory.
		return lt2Cmp(v.ID < w.ID)
	}
	// OpSelect is a pseudo-op. We need to be more aggressive
	// regarding CSE to keep multiple OpSelect's of the same
	// argument from existing.
	if v.Op != OpSelect0 && v.Op != OpSelect1 && v.Op != OpSelectN {
		if tc := v.Type.Compare(w.Type); tc != types.CMPeq {
			return tc
		}
	}

if v.Aux != w.Aux {
		if v.Aux == nil {
			return types.CMPlt
		}
		if w.Aux == nil {
			return types.CMPgt
		}
		return lt2Cmp(auxIDs[v.Aux] < auxIDs[w.Aux])
	}

return types.CMPeq
}

// Sort values to make the initial partition.
type sortvalues struct {
	a      []*Value // array of values
	auxIDs auxmap   // aux -> aux ID map
}

func (sv sortvalues) Len() int      { return len(sv.a) }
func (sv sortvalues) Swap(i, j int) { sv.a[i], sv.a[j] = sv.a[j], sv.a[i] }
func (sv sortvalues) Less(i, j int) bool {
	v := sv.a[i]
	w := sv.a[j]
	if cmp := cmpVal(v, w, sv.auxIDs); cmp != types.CMPeq {
		return cmp == types.CMPlt
	}

// Sort by value ID last to keep the sort result deterministic.
	return v.ID < w.ID
}

type partitionByDom struct {
	a    []*Value // array of values
	sdom SparseTree
}

func (sv partitionByDom) Len() int      { return len(sv.a) }
func (sv partitionByDom) Swap(i, j int) { sv.a[i], sv.a[j] = sv.a[j], sv.a[i] }
func (sv partitionByDom) Less(i, j int) bool {
	v := sv.a[i]
	w := sv.a[j]
	return sv.sdom.domorder(v.Block) < sv.sdom.domorder(w.Block)
}

type partitionByArgClass struct {
	a       []*Value // array of values
	eqClass []ID     // equivalence class IDs of values
}

func (sv partitionByArgClass) Len() int      { return len(sv.a) }
func (sv partitionByArgClass) Swap(i, j int) { sv.a[i], sv.a[j] = sv.a[j], sv.a[i] }
func (sv partitionByArgClass) Less(i, j int) bool {
	v := sv.a[i]
	w := sv.a[j]
	for i, a := range v.Args {
		b := w.Args[i]
		if sv.eqClass[a.ID] < sv.eqClass[b.ID] {
			return true
		}
		if sv.eqClass[a.ID] > sv.eqClass[b.ID] {
			return false
		}
	}
	return false
}

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Editing: cse.go

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