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compiler: rename named unused global vars to "_"

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So that (*codegen).Visit is able to omit code generation for these
unused global vars. The most tricky part is to detect unused global
variables, it is done in several steps:
1. Collect the set of named used/unused global vars.
2. Collect the set of globally declared expressions that contain
function calls.
3. Pick up global vars from the set made at step 2.
4. Traverse used functions and puck up those global vars that are used
from these functions.
5. Rename all globals that are presented in the set made at step 1
but are not presented in the set made on step 3 or step 4.
This commit is contained in:
Anna Shaleva 2022-08-04 17:47:32 +03:00
parent 1e6b70d570
commit 800321db06
10 changed files with 903 additions and 22 deletions
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241
pkg/compiler/analysis.go
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@ -89,13 +89,10 @@ func (c *codegen) traverseGlobals() bool {
lastCnt, maxCnt := -1, -1
c.ForEachPackage(func(pkg *packages.Package) {
// TODO: @optimizeme: it could happen that we don't need the whole set of globals to be emitted.
// We don't need the code for unused var at all, but at the same time we need to emit code for those
// vars that have function call inside. Thus convertGlobals should be able to distinguish these cases.
if n+nConst > 0 || hasUnusedCall {
for _, f := range pkg.Syntax {
c.fillImportMap(f, pkg)
c.convertGlobals(f, pkg.Types)
c.convertGlobals(f)
}
}
for _, f := range pkg.Syntax {
@ -169,7 +166,7 @@ func countGlobals(f ast.Node, checkUnusedCalls bool) (int, int, bool) {
valueSpec := s.(*ast.ValueSpec)
multiRet := len(valueSpec.Values) != 0 && len(valueSpec.Names) != len(valueSpec.Values) // e.g. var A, B = f() where func f() (int, int)
for j, id := range valueSpec.Names {
if id.Name != "_" {
if id.Name != "_" { // If variable has name, then it's treated as used - that's countGlobals' caller responsibility to guarantee that.
if isVar {
numVar++
} else {
@ -284,21 +281,45 @@ func (c *codegen) fillDocumentInfo() {
})
}
// analyzeFuncUsage traverses all code and returns a map with functions
// analyzeFuncAndGlobalVarUsage traverses all code and returns a map with functions
// which should be present in the emitted code.
// This is done using BFS starting from exported functions or
// the function used in variable declarations (graph edge corresponds to
// the function being called in declaration).
func (c *codegen) analyzeFuncUsage() funcUsage {
// the function being called in declaration). It also analyzes global variables
// usage preserving the same traversal strategy and rules. Unused global variables
// are renamed to "_" in the end. Global variable is treated as "used" iff:
// 1. It belongs either to main or to exported package AND is used directly from the exported (or _init\_deploy) method of the main package.
// 2. It belongs either to main or to exported package AND is used non-directly from the exported (or _init\_deploy) method of the main package
// (e.g. via series of function calls or in some expression that is "used").
// 3. It belongs either to main or to exported package AND contains function call inside its value definition.
func (c *codegen) analyzeFuncAndGlobalVarUsage() funcUsage {
type declPair struct {
decl *ast.FuncDecl
importMap map[string]string
path string
}
// nodeCache contains top-level function declarations .
// globalVar represents a global variable declaration node with the corresponding package context.
type globalVar struct {
decl *ast.GenDecl // decl contains global variables declaration node (there can be multiple declarations in a single node).
specIdx int // specIdx is the index of variable specification in the list of GenDecl specifications.
varIdx int // varIdx is the index of variable name in the specification names.
ident *ast.Ident // ident is a named global variable identifier got from the specified node.
importMap map[string]string
path string
}
// nodeCache contains top-level function declarations.
nodeCache := make(map[string]declPair)
// globalVarsCache contains both used and unused declared named global vars.
globalVarsCache := make(map[string]globalVar)
// diff contains used functions that are not yet marked as "used" and those definition
// requires traversal in the subsequent stages.
diff := funcUsage{}
// globalVarsDiff contains used named global variables that are not yet marked as "used"
// and those declaration requires traversal in the subsequent stages.
globalVarsDiff := funcUsage{}
// usedExpressions contains a set of ast.Nodes that are used in the program and need to be evaluated
// (either they are used from the used functions OR belong to global variable declaration and surrounded by a function call)
var usedExpressions []nodeContext
c.ForEachFile(func(f *ast.File, pkg *types.Package) {
var pkgPath string
isMain := pkg == c.mainPkg.Types
@ -350,6 +371,44 @@ func (c *codegen) analyzeFuncUsage() funcUsage {
}
nodeCache[name] = declPair{n, c.importMap, pkgPath}
return false // will be processed in the next stage
case *ast.GenDecl:
// After skipping all funcDecls, we are sure that each value spec
// is a globally declared variable or constant. We need to gather global
// vars from both main and imported packages.
if n.Tok == token.VAR {
for i, s := range n.Specs {
valSpec := s.(*ast.ValueSpec)
for j, id := range valSpec.Names {
if id.Name != "_" {
name := c.getIdentName(pkgPath, id.Name)
globalVarsCache[name] = globalVar{
decl: n,
specIdx: i,
varIdx: j,
ident: id,
importMap: c.importMap,
path: pkgPath,
}
}
// Traverse both named/unnamed global variables, check whether function/method call
// is present inside variable value and if so, mark all its children as "used" for
// further traversal and evaluation.
if len(valSpec.Values) == 0 {
continue
}
multiRet := len(valSpec.Values) != len(valSpec.Names)
if (j == 0 || !multiRet) && containsCall(valSpec.Values[j]) {
usedExpressions = append(usedExpressions, nodeContext{
node: valSpec.Values[j],
path: pkgPath,
importMap: c.importMap,
typeInfo: c.typeInfo,
currPkg: c.currPkg,
})
}
}
}
}
}
return true
})
@ -358,9 +417,24 @@ func (c *codegen) analyzeFuncUsage() funcUsage {
return nil
}
// Handle nodes that contain (or surrounded by) function calls and are a part
// of global variable declaration.
c.pickVarsFromNodes(usedExpressions, func(name string) {
if _, gOK := globalVarsCache[name]; gOK {
globalVarsDiff[name] = true
}
})
// Traverse the set of upper-layered used functions and construct the functions' usage map.
// At the same time, go through the whole set of used functions and mark global vars used
// from these functions as "used". Also mark the global variables from the previous step
// and their children as "used".
usage := funcUsage{}
for len(diff) != 0 {
globalVarsUsage := funcUsage{}
for len(diff) != 0 || len(globalVarsDiff) != 0 {
nextDiff := funcUsage{}
nextGlobalVarsDiff := funcUsage{}
usedExpressions = usedExpressions[:0]
for name := range diff {
fd, ok := nodeCache[name]
if !ok || usage[name] {
@ -388,12 +462,157 @@ func (c *codegen) analyzeFuncUsage() funcUsage {
}
return true
})
usedExpressions = append(usedExpressions, nodeContext{
node: fd.decl.Body,
path: fd.path,
importMap: c.importMap,
typeInfo: c.typeInfo,
currPkg: c.currPkg,
})
}
// Traverse used global vars in a separate cycle so that we're sure there's no other unrelated vars.
// Mark their children as "used".
for name := range globalVarsDiff {
fd, ok := globalVarsCache[name]
if !ok || globalVarsUsage[name] {
continue
}
globalVarsUsage[name] = true
pkg := c.mainPkg
if fd.path != "" {
pkg = c.packageCache[fd.path]
}
valSpec := fd.decl.Specs[fd.specIdx].(*ast.ValueSpec)
if len(valSpec.Values) == 0 {
continue
}
multiRet := len(valSpec.Values) != len(valSpec.Names)
if fd.varIdx == 0 || !multiRet {
usedExpressions = append(usedExpressions, nodeContext{
node: valSpec.Values[fd.varIdx],
path: fd.path,
importMap: fd.importMap,
typeInfo: pkg.TypesInfo,
currPkg: pkg,
})
}
}
c.pickVarsFromNodes(usedExpressions, func(name string) {
if _, gOK := globalVarsCache[name]; gOK {
nextGlobalVarsDiff[name] = true
}
})
diff = nextDiff
globalVarsDiff = nextGlobalVarsDiff
}
// Tiny hack: rename all remaining unused global vars. After that these unused
// vars will be handled as any other unnamed unused variables, i.e.
// c.traverseGlobals() won't take them into account during static slot creation
// and the code won't be emitted for them.
for name, node := range globalVarsCache {
if _, ok := globalVarsUsage[name]; !ok {
node.ident.Name = "_"
}
}
return usage
}
// nodeContext contains ast node with the corresponding import map, type info and package information
// required to retrieve fully qualified node name (if so).
type nodeContext struct {
node ast.Node
path string
importMap map[string]string
typeInfo *types.Info
currPkg *packages.Package
}
// derive returns provided node with the parent's context.
func (c nodeContext) derive(n ast.Node) nodeContext {
return nodeContext{
node: n,
path: c.path,
importMap: c.importMap,
typeInfo: c.typeInfo,
currPkg: c.currPkg,
}
}
// pickVarsFromNodes searches for variables used in the given set of nodes
// calling markAsUsed for each variable. Be careful while using codegen after
// pickVarsFromNodes, it changes importMap, currPkg and typeInfo.
func (c *codegen) pickVarsFromNodes(nodes []nodeContext, markAsUsed func(name string)) {
for len(nodes) != 0 {
var nextExprToCheck []nodeContext
for _, val := range nodes {
// Set variable context for proper name extraction.
c.importMap = val.importMap
c.currPkg = val.currPkg
c.typeInfo = val.typeInfo
ast.Inspect(val.node, func(node ast.Node) bool {
switch n := node.(type) {
case *ast.KeyValueExpr: // var _ = f() + CustomInt{Int: Unused}.Int + 3 => mark Unused as "used".
nextExprToCheck = append(nextExprToCheck, val.derive(n.Value))
return false
case *ast.CallExpr:
switch t := n.Fun.(type) {
case *ast.Ident:
// Do nothing, used functions are handled in a separate cycle.
case *ast.SelectorExpr:
nextExprToCheck = append(nextExprToCheck, val.derive(t))
}
for _, arg := range n.Args {
switch arg.(type) {
case *ast.BasicLit:
default:
nextExprToCheck = append(nextExprToCheck, val.derive(arg))
}
}
return false
case *ast.SelectorExpr:
if c.typeInfo.Selections[n] != nil {
switch t := n.X.(type) {
case *ast.Ident:
nextExprToCheck = append(nextExprToCheck, val.derive(t))
case *ast.CompositeLit:
nextExprToCheck = append(nextExprToCheck, val.derive(t))
case *ast.SelectorExpr: // imp_pkg.Anna.GetAge() => mark Anna (exported global struct) as used.
nextExprToCheck = append(nextExprToCheck, val.derive(t))
}
} else {
ident := n.X.(*ast.Ident)
name := c.getIdentName(ident.Name, n.Sel.Name)
markAsUsed(name)
}
return false
case *ast.CompositeLit: // var _ = f(1) + []int{1, Unused, 3}[1] => mark Unused as "used".
for _, e := range n.Elts {
switch e.(type) {
case *ast.BasicLit:
default:
nextExprToCheck = append(nextExprToCheck, val.derive(e))
}
}
return false
case *ast.Ident:
name := c.getIdentName(val.path, n.Name)
markAsUsed(name)
return false
case *ast.DeferStmt:
nextExprToCheck = append(nextExprToCheck, val.derive(n.Call.Fun))
return false
case *ast.BasicLit:
return false
}
return true
})
}
nodes = nextExprToCheck
}
}
func isGoBuiltin(name string) bool {
for i := range goBuiltins {
if name == goBuiltins[i] {