Source file src/cmd/compile/internal/pgoir/irgraph.go
1 // Copyright 2022 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. 4 5 // A note on line numbers: when working with line numbers, we always use the 6 // binary-visible relative line number. i.e., the line number as adjusted by 7 // //line directives (ctxt.InnermostPos(ir.Node.Pos()).RelLine()). Use 8 // NodeLineOffset to compute line offsets. 9 // 10 // If you are thinking, "wait, doesn't that just make things more complex than 11 // using the real line number?", then you are 100% correct. Unfortunately, 12 // pprof profiles generated by the runtime always contain line numbers as 13 // adjusted by //line directives (because that is what we put in pclntab). Thus 14 // for the best behavior when attempting to match the source with the profile 15 // it makes sense to use the same line number space. 16 // 17 // Some of the effects of this to keep in mind: 18 // 19 // - For files without //line directives there is no impact, as RelLine() == 20 // Line(). 21 // - For functions entirely covered by the same //line directive (i.e., a 22 // directive before the function definition and no directives within the 23 // function), there should also be no impact, as line offsets within the 24 // function should be the same as the real line offsets. 25 // - Functions containing //line directives may be impacted. As fake line 26 // numbers need not be monotonic, we may compute negative line offsets. We 27 // should accept these and attempt to use them for best-effort matching, as 28 // these offsets should still match if the source is unchanged, and may 29 // continue to match with changed source depending on the impact of the 30 // changes on fake line numbers. 31 // - Functions containing //line directives may also contain duplicate lines, 32 // making it ambiguous which call the profile is referencing. This is a 33 // similar problem to multiple calls on a single real line, as we don't 34 // currently track column numbers. 35 // 36 // Long term it would be best to extend pprof profiles to include real line 37 // numbers. Until then, we have to live with these complexities. Luckily, 38 // //line directives that change line numbers in strange ways should be rare, 39 // and failing PGO matching on these files is not too big of a loss. 40 41 // Package pgoir associates a PGO profile with the IR of the current package 42 // compilation. 43 package pgoir 44 45 import ( 46 "bufio" 47 "cmd/compile/internal/base" 48 "cmd/compile/internal/ir" 49 "cmd/compile/internal/typecheck" 50 "cmd/compile/internal/types" 51 "cmd/internal/pgo" 52 "fmt" 53 "maps" 54 "os" 55 ) 56 57 // IRGraph is a call graph with nodes pointing to IRs of functions and edges 58 // carrying weights and callsite information. 59 // 60 // Nodes for indirect calls may have missing IR (IRNode.AST == nil) if the node 61 // is not visible from this package (e.g., not in the transitive deps). Keeping 62 // these nodes allows determining the hottest edge from a call even if that 63 // callee is not available. 64 // 65 // TODO(prattmic): Consider merging this data structure with Graph. This is 66 // effectively a copy of Graph aggregated to line number and pointing to IR. 67 type IRGraph struct { 68 // Nodes of the graph. Each node represents a function, keyed by linker 69 // symbol name. 70 IRNodes map[string]*IRNode 71 } 72 73 // IRNode represents a node (function) in the IRGraph. 74 type IRNode struct { 75 // Pointer to the IR of the Function represented by this node. 76 AST *ir.Func 77 // Linker symbol name of the Function represented by this node. 78 // Populated only if AST == nil. 79 LinkerSymbolName string 80 81 // Set of out-edges in the callgraph. The map uniquely identifies each 82 // edge based on the callsite and callee, for fast lookup. 83 OutEdges map[pgo.NamedCallEdge]*IREdge 84 } 85 86 // Name returns the symbol name of this function. 87 func (i *IRNode) Name() string { 88 if i.AST != nil { 89 return ir.LinkFuncName(i.AST) 90 } 91 return i.LinkerSymbolName 92 } 93 94 // IREdge represents a call edge in the IRGraph with source, destination, 95 // weight, callsite, and line number information. 96 type IREdge struct { 97 // Source and destination of the edge in IRNode. 98 Src, Dst *IRNode 99 Weight int64 100 CallSiteOffset int // Line offset from function start line. 101 } 102 103 // CallSiteInfo captures call-site information and its caller/callee. 104 type CallSiteInfo struct { 105 LineOffset int // Line offset from function start line. 106 Caller *ir.Func 107 Callee *ir.Func 108 } 109 110 // Profile contains the processed PGO profile and weighted call graph used for 111 // PGO optimizations. 112 type Profile struct { 113 // Profile is the base data from the raw profile, without IR attribution. 114 *pgo.Profile 115 116 // WeightedCG represents the IRGraph built from profile, which we will 117 // update as part of inlining. 118 WeightedCG *IRGraph 119 } 120 121 // New generates a profile-graph from the profile or pre-processed profile. 122 func New(profileFile string) (*Profile, error) { 123 f, err := os.Open(profileFile) 124 if err != nil { 125 return nil, fmt.Errorf("error opening profile: %w", err) 126 } 127 defer f.Close() 128 r := bufio.NewReader(f) 129 130 isSerialized, err := pgo.IsSerialized(r) 131 if err != nil { 132 return nil, fmt.Errorf("error processing profile header: %w", err) 133 } 134 135 var base *pgo.Profile 136 if isSerialized { 137 base, err = pgo.FromSerialized(r) 138 if err != nil { 139 return nil, fmt.Errorf("error processing serialized PGO profile: %w", err) 140 } 141 } else { 142 base, err = pgo.FromPProf(r) 143 if err != nil { 144 return nil, fmt.Errorf("error processing pprof PGO profile: %w", err) 145 } 146 } 147 148 if base.TotalWeight == 0 { 149 return nil, nil // accept but ignore profile with no samples. 150 } 151 152 // Create package-level call graph with weights from profile and IR. 153 wg := createIRGraph(base.NamedEdgeMap) 154 155 return &Profile{ 156 Profile: base, 157 WeightedCG: wg, 158 }, nil 159 } 160 161 // initializeIRGraph builds the IRGraph by visiting all the ir.Func in decl list 162 // of a package. 163 func createIRGraph(namedEdgeMap pgo.NamedEdgeMap) *IRGraph { 164 g := &IRGraph{ 165 IRNodes: make(map[string]*IRNode), 166 } 167 168 // Bottomup walk over the function to create IRGraph. 169 ir.VisitFuncsBottomUp(typecheck.Target.Funcs, func(list []*ir.Func, recursive bool) { 170 for _, fn := range list { 171 visitIR(fn, namedEdgeMap, g) 172 } 173 }) 174 175 // Add additional edges for indirect calls. This must be done second so 176 // that IRNodes is fully populated (see the dummy node TODO in 177 // addIndirectEdges). 178 // 179 // TODO(prattmic): visitIR above populates the graph via direct calls 180 // discovered via the IR. addIndirectEdges populates the graph via 181 // calls discovered via the profile. This combination of opposite 182 // approaches is a bit awkward, particularly because direct calls are 183 // discoverable via the profile as well. Unify these into a single 184 // approach. 185 addIndirectEdges(g, namedEdgeMap) 186 187 return g 188 } 189 190 // visitIR traverses the body of each ir.Func adds edges to g from ir.Func to 191 // any called function in the body. 192 func visitIR(fn *ir.Func, namedEdgeMap pgo.NamedEdgeMap, g *IRGraph) { 193 name := ir.LinkFuncName(fn) 194 node, ok := g.IRNodes[name] 195 if !ok { 196 node = &IRNode{ 197 AST: fn, 198 } 199 g.IRNodes[name] = node 200 } 201 202 // Recursively walk over the body of the function to create IRGraph edges. 203 createIRGraphEdge(fn, node, name, namedEdgeMap, g) 204 } 205 206 // createIRGraphEdge traverses the nodes in the body of ir.Func and adds edges 207 // between the callernode which points to the ir.Func and the nodes in the 208 // body. 209 func createIRGraphEdge(fn *ir.Func, callernode *IRNode, name string, namedEdgeMap pgo.NamedEdgeMap, g *IRGraph) { 210 ir.VisitList(fn.Body, func(n ir.Node) { 211 switch n.Op() { 212 case ir.OCALLFUNC: 213 call := n.(*ir.CallExpr) 214 // Find the callee function from the call site and add the edge. 215 callee := DirectCallee(call.Fun) 216 if callee != nil { 217 addIREdge(callernode, name, n, callee, namedEdgeMap, g) 218 } 219 case ir.OCALLMETH: 220 call := n.(*ir.CallExpr) 221 // Find the callee method from the call site and add the edge. 222 callee := ir.MethodExprName(call.Fun).Func 223 addIREdge(callernode, name, n, callee, namedEdgeMap, g) 224 } 225 }) 226 } 227 228 // NodeLineOffset returns the line offset of n in fn. 229 func NodeLineOffset(n ir.Node, fn *ir.Func) int { 230 // See "A note on line numbers" at the top of the file. 231 line := int(base.Ctxt.InnermostPos(n.Pos()).RelLine()) 232 startLine := int(base.Ctxt.InnermostPos(fn.Pos()).RelLine()) 233 return line - startLine 234 } 235 236 // addIREdge adds an edge between caller and new node that points to `callee` 237 // based on the profile-graph and NodeMap. 238 func addIREdge(callerNode *IRNode, callerName string, call ir.Node, callee *ir.Func, namedEdgeMap pgo.NamedEdgeMap, g *IRGraph) { 239 calleeName := ir.LinkFuncName(callee) 240 calleeNode, ok := g.IRNodes[calleeName] 241 if !ok { 242 calleeNode = &IRNode{ 243 AST: callee, 244 } 245 g.IRNodes[calleeName] = calleeNode 246 } 247 248 namedEdge := pgo.NamedCallEdge{ 249 CallerName: callerName, 250 CalleeName: calleeName, 251 CallSiteOffset: NodeLineOffset(call, callerNode.AST), 252 } 253 254 // Add edge in the IRGraph from caller to callee. 255 edge := &IREdge{ 256 Src: callerNode, 257 Dst: calleeNode, 258 Weight: namedEdgeMap.Weight[namedEdge], 259 CallSiteOffset: namedEdge.CallSiteOffset, 260 } 261 262 if callerNode.OutEdges == nil { 263 callerNode.OutEdges = make(map[pgo.NamedCallEdge]*IREdge) 264 } 265 callerNode.OutEdges[namedEdge] = edge 266 } 267 268 // LookupFunc looks up a function or method in export data. It is expected to 269 // be overridden by package noder, to break a dependency cycle. 270 var LookupFunc = func(fullName string) (*ir.Func, error) { 271 base.Fatalf("pgoir.LookupMethodFunc not overridden") 272 panic("unreachable") 273 } 274 275 // PostLookupCleanup performs any remaining cleanup operations needed 276 // after a series of calls to LookupFunc, specifically reading in the 277 // bodies of functions that may have been delayed due being encountered 278 // in a stage where the reader's curfn state was not set up. 279 var PostLookupCleanup = func() { 280 base.Fatalf("pgoir.PostLookupCleanup not overridden") 281 panic("unreachable") 282 } 283 284 // addIndirectEdges adds indirect call edges found in the profile to the graph, 285 // to be used for devirtualization. 286 // 287 // N.B. despite the name, addIndirectEdges will add any edges discovered via 288 // the profile. We don't know for sure that they are indirect, but assume they 289 // are since direct calls would already be added. (e.g., direct calls that have 290 // been deleted from source since the profile was taken would be added here). 291 // 292 // TODO(prattmic): Devirtualization runs before inlining, so we can't devirtualize 293 // calls inside inlined call bodies. If we did add that, we'd need edges from 294 // inlined bodies as well. 295 func addIndirectEdges(g *IRGraph, namedEdgeMap pgo.NamedEdgeMap) { 296 // g.IRNodes is populated with the set of functions in the local 297 // package build by VisitIR. We want to filter for local functions 298 // below, but we also add unknown callees to IRNodes as we go. So make 299 // an initial copy of IRNodes to recall just the local functions. 300 localNodes := maps.Clone(g.IRNodes) 301 302 // N.B. We must consider edges in a stable order because export data 303 // lookup order (LookupMethodFunc, below) can impact the export data of 304 // this package, which must be stable across different invocations for 305 // reproducibility. 306 // 307 // The weight ordering of ByWeight is irrelevant, it just happens to be 308 // an ordered list of edges that is already available. 309 for _, key := range namedEdgeMap.ByWeight { 310 weight := namedEdgeMap.Weight[key] 311 // All callers in the local package build were added to IRNodes 312 // in VisitIR. If a caller isn't in the local package build we 313 // can skip adding edges, since we won't be devirtualizing in 314 // them anyway. This keeps the graph smaller. 315 callerNode, ok := localNodes[key.CallerName] 316 if !ok { 317 continue 318 } 319 320 // Already handled this edge? 321 if _, ok := callerNode.OutEdges[key]; ok { 322 continue 323 } 324 325 calleeNode, ok := g.IRNodes[key.CalleeName] 326 if !ok { 327 // IR is missing for this callee. VisitIR populates 328 // IRNodes with all functions discovered via local 329 // package function declarations and calls. This 330 // function may still be available from export data of 331 // a transitive dependency. 332 // 333 // TODO(prattmic): Parameterized types/functions are 334 // not supported. 335 // 336 // TODO(prattmic): This eager lookup during graph load 337 // is simple, but wasteful. We are likely to load many 338 // functions that we never need. We could delay load 339 // until we actually need the method in 340 // devirtualization. Instantiation of generic functions 341 // will likely need to be done at the devirtualization 342 // site, if at all. 343 if base.Debug.PGODebug >= 3 { 344 fmt.Printf("addIndirectEdges: %s attempting export data lookup\n", key.CalleeName) 345 } 346 fn, err := LookupFunc(key.CalleeName) 347 if err == nil { 348 if base.Debug.PGODebug >= 3 { 349 fmt.Printf("addIndirectEdges: %s found in export data\n", key.CalleeName) 350 } 351 calleeNode = &IRNode{AST: fn} 352 353 // N.B. we could call createIRGraphEdge to add 354 // direct calls in this newly-imported 355 // function's body to the graph. Similarly, we 356 // could add to this function's queue to add 357 // indirect calls. However, those would be 358 // useless given the visit order of inlining, 359 // and the ordering of PGO devirtualization and 360 // inlining. This function can only be used as 361 // an inlined body. We will never do PGO 362 // devirtualization inside an inlined call. Nor 363 // will we perform inlining inside an inlined 364 // call. 365 } else { 366 // Still not found. Most likely this is because 367 // the callee isn't in the transitive deps of 368 // this package. 369 // 370 // Record this call anyway. If this is the hottest, 371 // then we want to skip devirtualization rather than 372 // devirtualizing to the second most common callee. 373 if base.Debug.PGODebug >= 3 { 374 fmt.Printf("addIndirectEdges: %s not found in export data: %v\n", key.CalleeName, err) 375 } 376 calleeNode = &IRNode{LinkerSymbolName: key.CalleeName} 377 } 378 379 // Add dummy node back to IRNodes. We don't need this 380 // directly, but PrintWeightedCallGraphDOT uses these 381 // to print nodes. 382 g.IRNodes[key.CalleeName] = calleeNode 383 } 384 edge := &IREdge{ 385 Src: callerNode, 386 Dst: calleeNode, 387 Weight: weight, 388 CallSiteOffset: key.CallSiteOffset, 389 } 390 391 if callerNode.OutEdges == nil { 392 callerNode.OutEdges = make(map[pgo.NamedCallEdge]*IREdge) 393 } 394 callerNode.OutEdges[key] = edge 395 } 396 397 PostLookupCleanup() 398 } 399 400 // PrintWeightedCallGraphDOT prints IRGraph in DOT format. 401 func (p *Profile) PrintWeightedCallGraphDOT(edgeThreshold float64) { 402 fmt.Printf("\ndigraph G {\n") 403 fmt.Printf("forcelabels=true;\n") 404 405 // List of functions in this package. 406 funcs := make(map[string]struct{}) 407 ir.VisitFuncsBottomUp(typecheck.Target.Funcs, func(list []*ir.Func, recursive bool) { 408 for _, f := range list { 409 name := ir.LinkFuncName(f) 410 funcs[name] = struct{}{} 411 } 412 }) 413 414 // Determine nodes of DOT. 415 // 416 // Note that ir.Func may be nil for functions not visible from this 417 // package. 418 nodes := make(map[string]*ir.Func) 419 for name := range funcs { 420 if n, ok := p.WeightedCG.IRNodes[name]; ok { 421 for _, e := range n.OutEdges { 422 if _, ok := nodes[e.Src.Name()]; !ok { 423 nodes[e.Src.Name()] = e.Src.AST 424 } 425 if _, ok := nodes[e.Dst.Name()]; !ok { 426 nodes[e.Dst.Name()] = e.Dst.AST 427 } 428 } 429 if _, ok := nodes[n.Name()]; !ok { 430 nodes[n.Name()] = n.AST 431 } 432 } 433 } 434 435 // Print nodes. 436 for name, ast := range nodes { 437 if _, ok := p.WeightedCG.IRNodes[name]; ok { 438 style := "solid" 439 if ast == nil { 440 style = "dashed" 441 } 442 443 if ast != nil && ast.Inl != nil { 444 fmt.Printf("\"%v\" [color=black, style=%s, label=\"%v,inl_cost=%d\"];\n", name, style, name, ast.Inl.Cost) 445 } else { 446 fmt.Printf("\"%v\" [color=black, style=%s, label=\"%v\"];\n", name, style, name) 447 } 448 } 449 } 450 // Print edges. 451 ir.VisitFuncsBottomUp(typecheck.Target.Funcs, func(list []*ir.Func, recursive bool) { 452 for _, f := range list { 453 name := ir.LinkFuncName(f) 454 if n, ok := p.WeightedCG.IRNodes[name]; ok { 455 for _, e := range n.OutEdges { 456 style := "solid" 457 if e.Dst.AST == nil { 458 style = "dashed" 459 } 460 color := "black" 461 edgepercent := pgo.WeightInPercentage(e.Weight, p.TotalWeight) 462 if edgepercent > edgeThreshold { 463 color = "red" 464 } 465 466 fmt.Printf("edge [color=%s, style=%s];\n", color, style) 467 fmt.Printf("\"%v\" -> \"%v\" [label=\"%.2f\"];\n", n.Name(), e.Dst.Name(), edgepercent) 468 } 469 } 470 } 471 }) 472 fmt.Printf("}\n") 473 } 474 475 // DirectCallee takes a function-typed expression and returns the underlying 476 // function that it refers to if statically known. Otherwise, it returns nil. 477 // 478 // Equivalent to inline.inlCallee without calling CanInline on closures. 479 func DirectCallee(fn ir.Node) *ir.Func { 480 fn = ir.StaticValue(fn) 481 switch fn.Op() { 482 case ir.OMETHEXPR: 483 fn := fn.(*ir.SelectorExpr) 484 n := ir.MethodExprName(fn) 485 // Check that receiver type matches fn.X. 486 // TODO(mdempsky): Handle implicit dereference 487 // of pointer receiver argument? 488 if n == nil || !types.Identical(n.Type().Recv().Type, fn.X.Type()) { 489 return nil 490 } 491 return n.Func 492 case ir.ONAME: 493 fn := fn.(*ir.Name) 494 if fn.Class == ir.PFUNC { 495 return fn.Func 496 } 497 case ir.OCLOSURE: 498 fn := fn.(*ir.ClosureExpr) 499 c := fn.Func 500 return c 501 } 502 return nil 503 } 504