blob: b95ea37d59b11e2cc086cf1068eb0aa5a22cc6ff [file] [log] [blame] [edit]
// 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.
package inlheur
import (
"cmd/compile/internal/ir"
"fmt"
"os"
)
// This file contains code to re-score callsites based on how the
// results of the call were used. Example:
//
// func foo() {
// x, fptr := bar()
// switch x {
// case 10: fptr = baz()
// default: blix()
// }
// fptr(100)
// }
//
// The initial scoring pass will assign a score to "bar()" based on
// various criteria, however once the first pass of scoring is done,
// we look at the flags on the result from bar, and check to see
// how those results are used. If bar() always returns the same constant
// for its first result, and if the variable receiving that result
// isn't redefined, and if that variable feeds into an if/switch
// condition, then we will try to adjust the score for "bar" (on the
// theory that if we inlined, we can constant fold / deadcode).
type resultPropAndCS struct {
defcs *CallSite
props ResultPropBits
}
type resultUseAnalyzer struct {
resultNameTab map[*ir.Name]resultPropAndCS
fn *ir.Func
cstab CallSiteTab
*condLevelTracker
}
// rescoreBasedOnCallResultUses examines how call results are used,
// and tries to update the scores of calls based on how their results
// are used in the function.
func (csa *callSiteAnalyzer) rescoreBasedOnCallResultUses(fn *ir.Func, resultNameTab map[*ir.Name]resultPropAndCS, cstab CallSiteTab) {
enableDebugTraceIfEnv()
rua := &resultUseAnalyzer{
resultNameTab: resultNameTab,
fn: fn,
cstab: cstab,
condLevelTracker: new(condLevelTracker),
}
var doNode func(ir.Node) bool
doNode = func(n ir.Node) bool {
rua.nodeVisitPre(n)
ir.DoChildren(n, doNode)
rua.nodeVisitPost(n)
return false
}
doNode(fn)
disableDebugTrace()
}
func (csa *callSiteAnalyzer) examineCallResults(cs *CallSite, resultNameTab map[*ir.Name]resultPropAndCS) map[*ir.Name]resultPropAndCS {
if debugTrace&debugTraceScoring != 0 {
fmt.Fprintf(os.Stderr, "=-= examining call results for %q\n",
EncodeCallSiteKey(cs))
}
// Invoke a helper to pick out the specific ir.Name's the results
// from this call are assigned into, e.g. "x, y := fooBar()". If
// the call is not part of an assignment statement, or if the
// variables in question are not newly defined, then we'll receive
// an empty list here.
//
names, autoTemps, props := namesDefined(cs)
if len(names) == 0 {
return resultNameTab
}
if debugTrace&debugTraceScoring != 0 {
fmt.Fprintf(os.Stderr, "=-= %d names defined\n", len(names))
}
// For each returned value, if the value has interesting
// properties (ex: always returns the same constant), and the name
// in question is never redefined, then make an entry in the
// result table for it.
const interesting = (ResultIsConcreteTypeConvertedToInterface |
ResultAlwaysSameConstant | ResultAlwaysSameInlinableFunc | ResultAlwaysSameFunc)
for idx, n := range names {
rprop := props.ResultFlags[idx]
if debugTrace&debugTraceScoring != 0 {
fmt.Fprintf(os.Stderr, "=-= props for ret %d %q: %s\n",
idx, n.Sym().Name, rprop.String())
}
if rprop&interesting == 0 {
continue
}
if csa.nameFinder.reassigned(n) {
continue
}
if resultNameTab == nil {
resultNameTab = make(map[*ir.Name]resultPropAndCS)
} else if _, ok := resultNameTab[n]; ok {
panic("should never happen")
}
entry := resultPropAndCS{
defcs: cs,
props: rprop,
}
resultNameTab[n] = entry
if autoTemps[idx] != nil {
resultNameTab[autoTemps[idx]] = entry
}
if debugTrace&debugTraceScoring != 0 {
fmt.Fprintf(os.Stderr, "=-= add resultNameTab table entry n=%v autotemp=%v props=%s\n", n, autoTemps[idx], rprop.String())
}
}
return resultNameTab
}
// namesDefined returns a list of ir.Name's corresponding to locals
// that receive the results from the call at site 'cs', plus the
// properties object for the called function. If a given result
// isn't cleanly assigned to a newly defined local, the
// slot for that result in the returned list will be nil. Example:
//
// call returned name list
//
// x := foo() [ x ]
// z, y := bar() [ nil, nil ]
// _, q := baz() [ nil, q ]
//
// In the case of a multi-return call, such as "x, y := foo()",
// the pattern we see from the front end will be a call op
// assigning to auto-temps, and then an assignment of the auto-temps
// to the user-level variables. In such cases we return
// first the user-level variable (in the first func result)
// and then the auto-temp name in the second result.
func namesDefined(cs *CallSite) ([]*ir.Name, []*ir.Name, *FuncProps) {
// If this call doesn't feed into an assignment (and of course not
// all calls do), then we don't have anything to work with here.
if cs.Assign == nil {
return nil, nil, nil
}
funcInlHeur, ok := fpmap[cs.Callee]
if !ok {
// TODO: add an assert/panic here.
return nil, nil, nil
}
if len(funcInlHeur.props.ResultFlags) == 0 {
return nil, nil, nil
}
// Single return case.
if len(funcInlHeur.props.ResultFlags) == 1 {
asgn, ok := cs.Assign.(*ir.AssignStmt)
if !ok {
return nil, nil, nil
}
// locate name being assigned
aname, ok := asgn.X.(*ir.Name)
if !ok {
return nil, nil, nil
}
return []*ir.Name{aname}, []*ir.Name{nil}, funcInlHeur.props
}
// Multi-return case
asgn, ok := cs.Assign.(*ir.AssignListStmt)
if !ok || !asgn.Def {
return nil, nil, nil
}
userVars := make([]*ir.Name, len(funcInlHeur.props.ResultFlags))
autoTemps := make([]*ir.Name, len(funcInlHeur.props.ResultFlags))
for idx, x := range asgn.Lhs {
if n, ok := x.(*ir.Name); ok {
userVars[idx] = n
r := asgn.Rhs[idx]
if r.Op() == ir.OCONVNOP {
r = r.(*ir.ConvExpr).X
}
if ir.IsAutoTmp(r) {
autoTemps[idx] = r.(*ir.Name)
}
if debugTrace&debugTraceScoring != 0 {
fmt.Fprintf(os.Stderr, "=-= multi-ret namedef uv=%v at=%v\n",
x, autoTemps[idx])
}
} else {
return nil, nil, nil
}
}
return userVars, autoTemps, funcInlHeur.props
}
func (rua *resultUseAnalyzer) nodeVisitPost(n ir.Node) {
rua.condLevelTracker.post(n)
}
func (rua *resultUseAnalyzer) nodeVisitPre(n ir.Node) {
rua.condLevelTracker.pre(n)
switch n.Op() {
case ir.OCALLINTER:
if debugTrace&debugTraceScoring != 0 {
fmt.Fprintf(os.Stderr, "=-= rescore examine iface call %v:\n", n)
}
rua.callTargetCheckResults(n)
case ir.OCALLFUNC:
if debugTrace&debugTraceScoring != 0 {
fmt.Fprintf(os.Stderr, "=-= rescore examine call %v:\n", n)
}
rua.callTargetCheckResults(n)
case ir.OIF:
ifst := n.(*ir.IfStmt)
rua.foldCheckResults(ifst.Cond)
case ir.OSWITCH:
swst := n.(*ir.SwitchStmt)
if swst.Tag != nil {
rua.foldCheckResults(swst.Tag)
}
}
}
// callTargetCheckResults examines a given call to see whether the
// callee expression is potentially an inlinable function returned
// from a potentially inlinable call. Examples:
//
// Scenario 1: named intermediate
//
// fn1 := foo() conc := bar()
// fn1("blah") conc.MyMethod()
//
// Scenario 2: returned func or concrete object feeds directly to call
//
// foo()("blah") bar().MyMethod()
//
// In the second case although at the source level the result of the
// direct call feeds right into the method call or indirect call,
// we're relying on the front end having inserted an auto-temp to
// capture the value.
func (rua *resultUseAnalyzer) callTargetCheckResults(call ir.Node) {
ce := call.(*ir.CallExpr)
rname := rua.getCallResultName(ce)
if rname == nil {
return
}
if debugTrace&debugTraceScoring != 0 {
fmt.Fprintf(os.Stderr, "=-= staticvalue returns %v:\n",
rname)
}
if rname.Class != ir.PAUTO {
return
}
switch call.Op() {
case ir.OCALLINTER:
if debugTrace&debugTraceScoring != 0 {
fmt.Fprintf(os.Stderr, "=-= in %s checking %v for cci prop:\n",
rua.fn.Sym().Name, rname)
}
if cs := rua.returnHasProp(rname, ResultIsConcreteTypeConvertedToInterface); cs != nil {
adj := returnFeedsConcreteToInterfaceCallAdj
cs.Score, cs.ScoreMask = adjustScore(adj, cs.Score, cs.ScoreMask)
}
case ir.OCALLFUNC:
if debugTrace&debugTraceScoring != 0 {
fmt.Fprintf(os.Stderr, "=-= in %s checking %v for samefunc props:\n",
rua.fn.Sym().Name, rname)
v, ok := rua.resultNameTab[rname]
if !ok {
fmt.Fprintf(os.Stderr, "=-= no entry for %v in rt\n", rname)
} else {
fmt.Fprintf(os.Stderr, "=-= props for %v: %q\n", rname, v.props.String())
}
}
if cs := rua.returnHasProp(rname, ResultAlwaysSameInlinableFunc); cs != nil {
adj := returnFeedsInlinableFuncToIndCallAdj
cs.Score, cs.ScoreMask = adjustScore(adj, cs.Score, cs.ScoreMask)
} else if cs := rua.returnHasProp(rname, ResultAlwaysSameFunc); cs != nil {
adj := returnFeedsFuncToIndCallAdj
cs.Score, cs.ScoreMask = adjustScore(adj, cs.Score, cs.ScoreMask)
}
}
}
// foldCheckResults examines the specified if/switch condition 'cond'
// to see if it refers to locals defined by a (potentially inlinable)
// function call at call site C, and if so, whether 'cond' contains
// only combinations of simple references to all of the names in
// 'names' with selected constants + operators. If these criteria are
// met, then we adjust the score for call site C to reflect the
// fact that inlining will enable deadcode and/or constant propagation.
// Note: for this heuristic to kick in, the names in question have to
// be all from the same callsite. Examples:
//
// q, r := baz() x, y := foo()
// switch q+r { a, b, c := bar()
// ... if x && y && a && b && c {
// } ...
// }
//
// For the call to "baz" above we apply a score adjustment, but not
// for the calls to "foo" or "bar".
func (rua *resultUseAnalyzer) foldCheckResults(cond ir.Node) {
namesUsed := collectNamesUsed(cond)
if len(namesUsed) == 0 {
return
}
var cs *CallSite
for _, n := range namesUsed {
rpcs, found := rua.resultNameTab[n]
if !found {
return
}
if cs != nil && rpcs.defcs != cs {
return
}
cs = rpcs.defcs
if rpcs.props&ResultAlwaysSameConstant == 0 {
return
}
}
if debugTrace&debugTraceScoring != 0 {
nls := func(nl []*ir.Name) string {
r := ""
for _, n := range nl {
r += " " + n.Sym().Name
}
return r
}
fmt.Fprintf(os.Stderr, "=-= calling ShouldFoldIfNameConstant on names={%s} cond=%v\n", nls(namesUsed), cond)
}
if !ShouldFoldIfNameConstant(cond, namesUsed) {
return
}
adj := returnFeedsConstToIfAdj
cs.Score, cs.ScoreMask = adjustScore(adj, cs.Score, cs.ScoreMask)
}
func collectNamesUsed(expr ir.Node) []*ir.Name {
res := []*ir.Name{}
ir.Visit(expr, func(n ir.Node) {
if n.Op() != ir.ONAME {
return
}
nn := n.(*ir.Name)
if nn.Class != ir.PAUTO {
return
}
res = append(res, nn)
})
return res
}
func (rua *resultUseAnalyzer) returnHasProp(name *ir.Name, prop ResultPropBits) *CallSite {
v, ok := rua.resultNameTab[name]
if !ok {
return nil
}
if v.props&prop == 0 {
return nil
}
return v.defcs
}
func (rua *resultUseAnalyzer) getCallResultName(ce *ir.CallExpr) *ir.Name {
var callTarg ir.Node
if sel, ok := ce.Fun.(*ir.SelectorExpr); ok {
// method call
callTarg = sel.X
} else if ctarg, ok := ce.Fun.(*ir.Name); ok {
// regular call
callTarg = ctarg
} else {
return nil
}
r := ir.StaticValue(callTarg)
if debugTrace&debugTraceScoring != 0 {
fmt.Fprintf(os.Stderr, "=-= staticname on %v returns %v:\n",
callTarg, r)
}
if r.Op() == ir.OCALLFUNC {
// This corresponds to the "x := foo()" case; here
// ir.StaticValue has brought us all the way back to
// the call expression itself. We need to back off to
// the name defined by the call; do this by looking up
// the callsite.
ce := r.(*ir.CallExpr)
cs, ok := rua.cstab[ce]
if !ok {
return nil
}
names, _, _ := namesDefined(cs)
if len(names) == 0 {
return nil
}
return names[0]
} else if r.Op() == ir.ONAME {
return r.(*ir.Name)
}
return nil
}