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cmd/compile/internal/inline: analyze function result properties
Add code to analyze properties of function result values, specifically heuristics for cases where we always return allocated memory, always return the same constant, or always return the same function. Updates #61502. Change-Id: I8b0a3295b5be7f7ad4c2d5b9803925aea0639376 Reviewed-on: https://go-review.googlesource.com/c/go/+/511559 Reviewed-by: Matthew Dempsky <mdempsky@google.com> LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
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260
src/cmd/compile/internal/inline/inlheur/analyze_func_returns.go
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,260 @@ | ||
| // Copyright 2023 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. | ||
|
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| package inlheur | ||
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||
| import ( | ||
| "cmd/compile/internal/ir" | ||
| "fmt" | ||
| "go/constant" | ||
| "go/token" | ||
| "os" | ||
| ) | ||
|
|
||
| // returnsAnalyzer stores state information for the process of | ||
| // computing flags/properties for the return values of a specific Go | ||
| // function, as part of inline heuristics synthesis. | ||
| type returnsAnalyzer struct { | ||
| fname string | ||
| props []ResultPropBits | ||
| values []resultVal | ||
| canInline func(*ir.Func) | ||
| } | ||
|
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||
| // resultVal captures information about a specific result returned from | ||
| // the function we're analyzing; we are interested in cases where | ||
| // the func always returns the same constant, or always returns | ||
| // the same function, etc. This container stores info on a the specific | ||
| // scenarios we're looking for. | ||
| type resultVal struct { | ||
| lit constant.Value | ||
| fn *ir.Name | ||
| fnClo bool | ||
| top bool | ||
| } | ||
|
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| func makeResultsAnalyzer(fn *ir.Func, canInline func(*ir.Func)) *returnsAnalyzer { | ||
| results := fn.Type().Results() | ||
| props := make([]ResultPropBits, len(results)) | ||
| vals := make([]resultVal, len(results)) | ||
| for i := range results { | ||
| rt := results[i].Type | ||
| if !rt.IsScalar() && !rt.HasNil() { | ||
| // existing properties not applicable here (for things | ||
| // like structs, arrays, slices, etc). | ||
| props[i] = ResultNoInfo | ||
| continue | ||
| } | ||
| // set the "top" flag (as in "top element of data flow lattice") | ||
| // meaning "we have no info yet, but we might later on". | ||
| vals[i].top = true | ||
| } | ||
| return &returnsAnalyzer{ | ||
| props: props, | ||
| values: vals, | ||
| canInline: canInline, | ||
| } | ||
| } | ||
|
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| // setResults transfers the calculated result properties for this | ||
| // function to 'fp'. | ||
| func (ra *returnsAnalyzer) setResults(fp *FuncProps) { | ||
| // Promote ResultAlwaysSameFunc to ResultAlwaysSameInlinableFunc | ||
| for i := range ra.values { | ||
| if ra.props[i] == ResultAlwaysSameFunc { | ||
| f := ra.values[i].fn.Func | ||
| // If the function being returns is a closure that hasn't | ||
| // yet been checked by CanInline, invoke it now. NB: this | ||
| // is hacky, it would be better if things were structured | ||
| // so that all closures were visited ahead of time. | ||
| if ra.values[i].fnClo { | ||
| if f != nil && !f.InlinabilityChecked() { | ||
| ra.canInline(f) | ||
| } | ||
| } | ||
| if f.Inl != nil { | ||
| ra.props[i] = ResultAlwaysSameInlinableFunc | ||
| } | ||
| } | ||
| } | ||
| fp.ResultFlags = ra.props | ||
| } | ||
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| func (ra *returnsAnalyzer) pessimize() { | ||
| for i := range ra.props { | ||
| ra.props[i] = ResultNoInfo | ||
| } | ||
| } | ||
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| func (ra *returnsAnalyzer) nodeVisitPre(n ir.Node) { | ||
| } | ||
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| func (ra *returnsAnalyzer) nodeVisitPost(n ir.Node) { | ||
| if len(ra.values) == 0 { | ||
| return | ||
| } | ||
| if n.Op() != ir.ORETURN { | ||
| return | ||
| } | ||
| if debugTrace&debugTraceResults != 0 { | ||
| fmt.Fprintf(os.Stderr, "=+= returns nodevis %v %s\n", | ||
| ir.Line(n), n.Op().String()) | ||
| } | ||
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| // No support currently for named results, so if we see an empty | ||
| // "return" stmt, be conservative. | ||
| rs := n.(*ir.ReturnStmt) | ||
| if len(rs.Results) != len(ra.values) { | ||
| ra.pessimize() | ||
| return | ||
| } | ||
| for i, r := range rs.Results { | ||
| ra.analyzeResult(i, r) | ||
| } | ||
| } | ||
|
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| // isFuncName returns the *ir.Name for the func or method | ||
| // corresponding to node 'n', along with a boolean indicating success, | ||
| // and another boolean indicating whether the func is closure. | ||
| func isFuncName(n ir.Node) (*ir.Name, bool, bool) { | ||
| sv := ir.StaticValue(n) | ||
| if sv.Op() == ir.ONAME { | ||
| name := sv.(*ir.Name) | ||
| if name.Sym() != nil && name.Class == ir.PFUNC { | ||
| return name, true, false | ||
| } | ||
| } | ||
| if sv.Op() == ir.OCLOSURE { | ||
| cloex := sv.(*ir.ClosureExpr) | ||
| return cloex.Func.Nname, true, true | ||
| } | ||
| if sv.Op() == ir.OMETHEXPR { | ||
| if mn := ir.MethodExprName(sv); mn != nil { | ||
| return mn, true, false | ||
| } | ||
| } | ||
| return nil, false, false | ||
| } | ||
|
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| // analyzeResult examines the expression 'n' being returned as the | ||
| // 'ii'th argument in some return statement to see whether has | ||
| // interesting characteristics (for example, returns a constant), then | ||
| // applies a dataflow "meet" operation to combine this result with any | ||
| // previous result (for the given return slot) that we've already | ||
| // processed. | ||
| func (ra *returnsAnalyzer) analyzeResult(ii int, n ir.Node) { | ||
| isAllocMem := isAllocatedMem(n) | ||
| isConcConvItf := isConcreteConvIface(n) | ||
| lit, isConst := isLiteral(n) | ||
| rfunc, isFunc, isClo := isFuncName(n) | ||
| curp := ra.props[ii] | ||
| newp := ResultNoInfo | ||
| var newlit constant.Value | ||
| var newfunc *ir.Name | ||
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| if debugTrace&debugTraceResults != 0 { | ||
| fmt.Fprintf(os.Stderr, "=-= %v: analyzeResult n=%s ismem=%v isconcconv=%v isconst=%v isfunc=%v isclo=%v\n", ir.Line(n), n.Op().String(), isAllocMem, isConcConvItf, isConst, isFunc, isClo) | ||
| } | ||
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| if ra.values[ii].top { | ||
| ra.values[ii].top = false | ||
| // this is the first return we've seen; record | ||
| // whatever properties it has. | ||
| switch { | ||
| case isAllocMem: | ||
| newp = ResultIsAllocatedMem | ||
| case isConcConvItf: | ||
| newp = ResultIsConcreteTypeConvertedToInterface | ||
| case isFunc: | ||
| newp = ResultAlwaysSameFunc | ||
| newfunc = rfunc | ||
| case isConst: | ||
| newp = ResultAlwaysSameConstant | ||
| newlit = lit | ||
| } | ||
| } else { | ||
| // this is not the first return we've seen; apply | ||
| // what amounts of a "meet" operator to combine | ||
| // the properties we see here with what we saw on | ||
| // the previous returns. | ||
| switch curp { | ||
| case ResultIsAllocatedMem: | ||
| if isAllocatedMem(n) { | ||
| newp = ResultIsAllocatedMem | ||
| } | ||
| case ResultIsConcreteTypeConvertedToInterface: | ||
| if isConcreteConvIface(n) { | ||
| newp = ResultIsConcreteTypeConvertedToInterface | ||
| } | ||
| case ResultAlwaysSameConstant: | ||
| if isConst && isSameLiteral(lit, ra.values[ii].lit) { | ||
| newp = ResultAlwaysSameConstant | ||
| newlit = lit | ||
| } | ||
| case ResultAlwaysSameFunc: | ||
| if isFunc && isSameFuncName(rfunc, ra.values[ii].fn) { | ||
| newp = ResultAlwaysSameFunc | ||
| newfunc = rfunc | ||
| } | ||
| } | ||
| } | ||
| ra.values[ii].fn = newfunc | ||
| ra.values[ii].fnClo = isClo | ||
| ra.values[ii].lit = newlit | ||
| ra.props[ii] = newp | ||
|
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| if debugTrace&debugTraceResults != 0 { | ||
| fmt.Fprintf(os.Stderr, "=-= %v: analyzeResult newp=%s\n", | ||
| ir.Line(n), newp) | ||
| } | ||
|
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| } | ||
|
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| func isAllocatedMem(n ir.Node) bool { | ||
| sv := ir.StaticValue(n) | ||
| switch sv.Op() { | ||
| case ir.OMAKESLICE, ir.ONEW, ir.OPTRLIT, ir.OSLICELIT: | ||
| return true | ||
| } | ||
| return false | ||
| } | ||
|
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| func isLiteral(n ir.Node) (constant.Value, bool) { | ||
| sv := ir.StaticValue(n) | ||
| if sv.Op() == ir.ONIL { | ||
| return nil, true | ||
| } | ||
| if sv.Op() != ir.OLITERAL { | ||
| return nil, false | ||
| } | ||
| ce := sv.(*ir.ConstExpr) | ||
| return ce.Val(), true | ||
| } | ||
|
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| // isSameLiteral checks to see if 'v1' and 'v2' correspond to the same | ||
| // literal value, or if they are both nil. | ||
| func isSameLiteral(v1, v2 constant.Value) bool { | ||
| if v1 == nil && v2 == nil { | ||
| return true | ||
| } | ||
| if v1 == nil || v2 == nil { | ||
| return false | ||
| } | ||
| return constant.Compare(v1, token.EQL, v2) | ||
| } | ||
|
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| func isConcreteConvIface(n ir.Node) bool { | ||
| sv := ir.StaticValue(n) | ||
| if sv.Op() != ir.OCONVIFACE { | ||
| return false | ||
| } | ||
| return !sv.(*ir.ConvExpr).X.Type().IsInterface() | ||
| } | ||
|
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| func isSameFuncName(v1, v2 *ir.Name) bool { | ||
| // NB: there are a few corner cases where pointer equality | ||
| // doesn't work here, but this should be good enough for | ||
| // our purposes here. | ||
| return v1 == v2 | ||
| } |
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