1 // Copyright 2023 The Go Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style
3 // license that can be found in the LICENSE file.
8 "cmd/compile/internal/ir"
13 // This file contains code to re-score callsites based on how the
14 // results of the call were used. Example:
19 // case 10: fptr = baz()
25 // The initial scoring pass will assign a score to "bar()" based on
26 // various criteria, however once the first pass of scoring is done,
27 // we look at the flags on the result from bar, and check to see
28 // how those results are used. If bar() always returns the same constant
29 // for its first result, and if the variable receiving that result
30 // isn't redefined, and if that variable feeds into an if/switch
31 // condition, then we will try to adjust the score for "bar" (on the
32 // theory that if we inlined, we can constant fold / deadcode).
34 type resultPropAndCS struct {
39 type resultUseAnalyzer struct {
40 resultNameTab map[*ir.Name]resultPropAndCS
46 // rescoreBasedOnCallResultUses examines how call results are used,
47 // and tries to update the scores of calls based on how their results
48 // are used in the function.
49 func rescoreBasedOnCallResultUses(fn *ir.Func, resultNameTab map[*ir.Name]resultPropAndCS, cstab CallSiteTab) {
50 enableDebugTraceIfEnv()
51 rua := &resultUseAnalyzer{
52 resultNameTab: resultNameTab,
55 condLevelTracker: new(condLevelTracker),
57 var doNode func(ir.Node) bool
58 doNode = func(n ir.Node) bool {
60 ir.DoChildren(n, doNode)
68 func examineCallResults(cs *CallSite, resultNameTab map[*ir.Name]resultPropAndCS) {
69 if debugTrace&debugTraceScoring != 0 {
70 fmt.Fprintf(os.Stderr, "=-= examining call results for %q\n",
71 EncodeCallSiteKey(cs))
74 // Invoke a helper to pick out the specific ir.Name's the results
75 // from this call are assigned into, e.g. "x, y := fooBar()". If
76 // the call is not part of an assignment statement, or if the
77 // variables in question are not newly defined, then we'll receive
78 // an empty list here.
80 names, autoTemps, props := namesDefined(cs)
85 if debugTrace&debugTraceScoring != 0 {
86 fmt.Fprintf(os.Stderr, "=-= %d names defined\n", len(names))
89 // For each returned value, if the value has interesting
90 // properties (ex: always returns the same constant), and the name
91 // in question is never redefined, then make an entry in the
92 // result table for it.
93 const interesting = (ResultIsConcreteTypeConvertedToInterface |
94 ResultAlwaysSameConstant | ResultAlwaysSameInlinableFunc | ResultAlwaysSameFunc)
95 for idx, n := range names {
96 rprop := props.ResultFlags[idx]
98 if debugTrace&debugTraceScoring != 0 {
99 fmt.Fprintf(os.Stderr, "=-= props for ret %d %q: %s\n",
100 idx, n.Sym().Name, rprop.String())
103 if rprop&interesting == 0 {
106 if ir.Reassigned(n) {
109 if _, ok := resultNameTab[n]; ok {
110 panic("should never happen")
112 entry := resultPropAndCS{
116 resultNameTab[n] = entry
117 if autoTemps[idx] != nil {
118 resultNameTab[autoTemps[idx]] = entry
120 if debugTrace&debugTraceScoring != 0 {
121 fmt.Fprintf(os.Stderr, "=-= add resultNameTab table entry n=%v autotemp=%v props=%s\n", n, autoTemps[idx], rprop.String())
126 // namesDefined returns a list of ir.Name's corresponding to locals
127 // that receive the results from the call at site 'cs', plus the
128 // properties object for the called function. If a given result
129 // isn't cleanly assigned to a newly defined local, the
130 // slot for that result in the returned list will be nil. Example:
132 // call returned name list
135 // z, y := bar() [ nil, nil ]
136 // _, q := baz() [ nil, q ]
138 // In the case of a multi-return call, such as "x, y := foo()",
139 // the pattern we see from the front end will be a call op
140 // assigning to auto-temps, and then an assignment of the auto-temps
141 // to the user-level variables. In such cases we return
142 // first the user-level variable (in the first func result)
143 // and then the auto-temp name in the second result.
144 func namesDefined(cs *CallSite) ([]*ir.Name, []*ir.Name, *FuncProps) {
145 // If this call doesn't feed into an assignment (and of course not
146 // all calls do), then we don't have anything to work with here.
147 if cs.Assign == nil {
150 funcInlHeur, ok := fpmap[cs.Callee]
152 // TODO: add an assert/panic here.
155 if len(funcInlHeur.props.ResultFlags) == 0 {
159 // Single return case.
160 if len(funcInlHeur.props.ResultFlags) == 1 {
161 asgn, ok := cs.Assign.(*ir.AssignStmt)
165 // locate name being assigned
166 aname, ok := asgn.X.(*ir.Name)
170 return []*ir.Name{aname}, []*ir.Name{nil}, funcInlHeur.props
174 asgn, ok := cs.Assign.(*ir.AssignListStmt)
175 if !ok || !asgn.Def {
178 userVars := make([]*ir.Name, len(funcInlHeur.props.ResultFlags))
179 autoTemps := make([]*ir.Name, len(funcInlHeur.props.ResultFlags))
180 for idx, x := range asgn.Lhs {
181 if n, ok := x.(*ir.Name); ok {
184 if r.Op() == ir.OCONVNOP {
185 r = r.(*ir.ConvExpr).X
188 autoTemps[idx] = r.(*ir.Name)
190 if debugTrace&debugTraceScoring != 0 {
191 fmt.Fprintf(os.Stderr, "=-= multi-ret namedef uv=%v at=%v\n",
198 return userVars, autoTemps, funcInlHeur.props
201 func (rua *resultUseAnalyzer) nodeVisitPost(n ir.Node) {
202 rua.condLevelTracker.post(n)
205 func (rua *resultUseAnalyzer) nodeVisitPre(n ir.Node) {
206 rua.condLevelTracker.pre(n)
209 if debugTrace&debugTraceScoring != 0 {
210 fmt.Fprintf(os.Stderr, "=-= rescore examine iface call %v:\n", n)
212 rua.callTargetCheckResults(n)
214 if debugTrace&debugTraceScoring != 0 {
215 fmt.Fprintf(os.Stderr, "=-= rescore examine call %v:\n", n)
217 rua.callTargetCheckResults(n)
219 ifst := n.(*ir.IfStmt)
220 rua.foldCheckResults(ifst.Cond)
222 swst := n.(*ir.SwitchStmt)
224 rua.foldCheckResults(swst.Tag)
230 // callTargetCheckResults examines a given call to see whether the
231 // callee expression is potentially an inlinable function returned
232 // from a potentially inlinable call. Examples:
234 // Scenario 1: named intermediate
236 // fn1 := foo() conc := bar()
237 // fn1("blah") conc.MyMethod()
239 // Scenario 2: returned func or concrete object feeds directly to call
241 // foo()("blah") bar().MyMethod()
243 // In the second case although at the source level the result of the
244 // direct call feeds right into the method call or indirect call,
245 // we're relying on the front end having inserted an auto-temp to
246 // capture the value.
247 func (rua *resultUseAnalyzer) callTargetCheckResults(call ir.Node) {
248 ce := call.(*ir.CallExpr)
249 rname := rua.getCallResultName(ce)
253 if debugTrace&debugTraceScoring != 0 {
254 fmt.Fprintf(os.Stderr, "=-= staticvalue returns %v:\n",
257 if rname.Class != ir.PAUTO {
262 if debugTrace&debugTraceScoring != 0 {
263 fmt.Fprintf(os.Stderr, "=-= in %s checking %v for cci prop:\n",
264 rua.fn.Sym().Name, rname)
266 if cs := rua.returnHasProp(rname, ResultIsConcreteTypeConvertedToInterface); cs != nil {
268 adj := returnFeedsConcreteToInterfaceCallAdj
269 cs.Score, cs.ScoreMask = adjustScore(adj, cs.Score, cs.ScoreMask)
272 if debugTrace&debugTraceScoring != 0 {
273 fmt.Fprintf(os.Stderr, "=-= in %s checking %v for samefunc props:\n",
274 rua.fn.Sym().Name, rname)
275 v, ok := rua.resultNameTab[rname]
277 fmt.Fprintf(os.Stderr, "=-= no entry for %v in rt\n", rname)
279 fmt.Fprintf(os.Stderr, "=-= props for %v: %q\n", rname, v.props.String())
282 if cs := rua.returnHasProp(rname, ResultAlwaysSameInlinableFunc); cs != nil {
283 adj := returnFeedsInlinableFuncToIndCallAdj
284 cs.Score, cs.ScoreMask = adjustScore(adj, cs.Score, cs.ScoreMask)
285 } else if cs := rua.returnHasProp(rname, ResultAlwaysSameFunc); cs != nil {
286 adj := returnFeedsFuncToIndCallAdj
287 cs.Score, cs.ScoreMask = adjustScore(adj, cs.Score, cs.ScoreMask)
293 // foldCheckResults examines the specified if/switch condition 'cond'
294 // to see if it refers to locals defined by a (potentially inlinable)
295 // function call at call site C, and if so, whether 'cond' contains
296 // only combinations of simple references to all of the names in
297 // 'names' with selected constants + operators. If these criteria are
298 // met, then we adjust the score for call site C to reflect the
299 // fact that inlining will enable deadcode and/or constant propagation.
300 // Note: for this heuristic to kick in, the names in question have to
301 // be all from the same callsite. Examples:
303 // q, r := baz() x, y := foo()
304 // switch q+r { a, b, c := bar()
305 // ... if x && y && a && b && c {
309 // For the call to "baz" above we apply a score adjustment, but not
310 // for the calls to "foo" or "bar".
311 func (rua *resultUseAnalyzer) foldCheckResults(cond ir.Node) {
312 namesUsed := collectNamesUsed(cond)
313 if len(namesUsed) == 0 {
317 for _, n := range namesUsed {
318 rpcs, found := rua.resultNameTab[n]
322 if cs != nil && rpcs.defcs != cs {
326 if rpcs.props&ResultAlwaysSameConstant == 0 {
330 if debugTrace&debugTraceScoring != 0 {
331 nls := func(nl []*ir.Name) string {
333 for _, n := range nl {
334 r += " " + n.Sym().Name
338 fmt.Fprintf(os.Stderr, "=-= calling ShouldFoldIfNameConstant on names={%s} cond=%v\n", nls(namesUsed), cond)
341 if !ShouldFoldIfNameConstant(cond, namesUsed) {
344 adj := returnFeedsConstToIfAdj
345 cs.Score, cs.ScoreMask = adjustScore(adj, cs.Score, cs.ScoreMask)
348 func collectNamesUsed(expr ir.Node) []*ir.Name {
350 ir.Visit(expr, func(n ir.Node) {
351 if n.Op() != ir.ONAME {
355 if nn.Class != ir.PAUTO {
358 res = append(res, nn)
363 func (rua *resultUseAnalyzer) returnHasProp(name *ir.Name, prop ResultPropBits) *CallSite {
364 v, ok := rua.resultNameTab[name]
368 if v.props&prop == 0 {
374 func (rua *resultUseAnalyzer) getCallResultName(ce *ir.CallExpr) *ir.Name {
376 if sel, ok := ce.Fun.(*ir.SelectorExpr); ok {
379 } else if ctarg, ok := ce.Fun.(*ir.Name); ok {
385 r := ir.StaticValue(callTarg)
386 if debugTrace&debugTraceScoring != 0 {
387 fmt.Fprintf(os.Stderr, "=-= staticname on %v returns %v:\n",
390 if r.Op() == ir.OCALLFUNC {
391 // This corresponds to the "x := foo()" case; here
392 // ir.StaticValue has brought us all the way back to
393 // the call expression itself. We need to back off to
394 // the name defined by the call; do this by looking up
396 ce := r.(*ir.CallExpr)
397 cs, ok := rua.cstab[ce]
401 names, _, _ := namesDefined(cs)
406 } else if r.Op() == ir.ONAME {