"fmt"
"internal/profile"
"os"
+ "sort"
)
// IRGraph is a call graph with nodes pointing to IRs of functions and edges
// TODO(prattmic): Consider merging this data structure with Graph. This is
// effectively a copy of Graph aggregated to line number and pointing to IR.
type IRGraph struct {
- // Nodes of the graph
+ // Nodes of the graph. Each node represents a function, keyed by linker
+ // symbol name.
IRNodes map[string]*IRNode
}
// Set of out-edges in the callgraph. The map uniquely identifies each
// edge based on the callsite and callee, for fast lookup.
- OutEdges map[NodeMapKey]*IREdge
+ OutEdges map[NamedCallEdge]*IREdge
}
// Name returns the symbol name of this function.
CallSiteOffset int // Line offset from function start line.
}
-// NodeMapKey represents a hash key to identify unique call-edges in profile
-// and in IR. Used for deduplication of call edges found in profile.
-//
-// TODO(prattmic): rename to something more descriptive.
-type NodeMapKey struct {
+// NamedCallEdge identifies a call edge by linker symbol names and call site
+// offset.
+type NamedCallEdge struct {
CallerName string
CalleeName string
CallSiteOffset int // Line offset from function start line.
}
-// Weights capture both node weight and edge weight.
-type Weights struct {
- NFlat int64
- NCum int64
- EWeight int64
+// NamedEdgeMap contains all unique call edges in the profile and their
+// edge weight.
+type NamedEdgeMap struct {
+ Weight map[NamedCallEdge]int64
+
+ // ByWeight lists all keys in Weight, sorted by edge weight.
+ ByWeight []NamedCallEdge
}
// CallSiteInfo captures call-site information and its caller/callee.
// Profile contains the processed PGO profile and weighted call graph used for
// PGO optimizations.
type Profile struct {
- // Aggregated NodeWeights and EdgeWeights across the profile. This
- // helps us determine the percentage threshold for hot/cold
- // partitioning.
- TotalNodeWeight int64
- TotalEdgeWeight int64
+ // Aggregated edge weights across the profile. This helps us determine
+ // the percentage threshold for hot/cold partitioning.
+ TotalWeight int64
- // NodeMap contains all unique call-edges in the profile and their
- // aggregated weight.
- NodeMap map[NodeMapKey]*Weights
+ // EdgeMap contains all unique call edges in the profile and their
+ // edge weight.
+ NamedEdgeMap NamedEdgeMap
// WeightedCG represents the IRGraph built from profile, which we will
// update as part of inlining.
SampleValue: func(v []int64) int64 { return v[valueIndex] },
})
- p := &Profile{
- NodeMap: make(map[NodeMapKey]*Weights),
- WeightedCG: &IRGraph{
- IRNodes: make(map[string]*IRNode),
- },
- }
-
- // Build the node map and totals from the profile graph.
- if err := p.processprofileGraph(g); err != nil {
+ namedEdgeMap, totalWeight, err := createNamedEdgeMap(g)
+ if err != nil {
return nil, err
}
- if p.TotalNodeWeight == 0 || p.TotalEdgeWeight == 0 {
+ if totalWeight == 0 {
return nil, nil // accept but ignore profile with no samples.
}
// Create package-level call graph with weights from profile and IR.
- p.initializeIRGraph()
+ wg := createIRGraph(namedEdgeMap)
- return p, nil
+ return &Profile{
+ TotalWeight: totalWeight,
+ NamedEdgeMap: namedEdgeMap,
+ WeightedCG: wg,
+ }, nil
}
-// processprofileGraph builds various maps from the profile-graph.
+// createNamedEdgeMap builds a map of callsite-callee edge weights from the
+// profile-graph.
//
-// It initializes NodeMap and Total{Node,Edge}Weight based on the name and
-// callsite to compute node and edge weights which will be used later on to
-// create edges for WeightedCG.
-//
-// Caller should ignore the profile if p.TotalNodeWeight == 0 || p.TotalEdgeWeight == 0.
-func (p *Profile) processprofileGraph(g *graph.Graph) error {
- nFlat := make(map[string]int64)
- nCum := make(map[string]int64)
+// Caller should ignore the profile if totalWeight == 0.
+func createNamedEdgeMap(g *graph.Graph) (edgeMap NamedEdgeMap, totalWeight int64, err error) {
seenStartLine := false
- // Accummulate weights for the same node.
- for _, n := range g.Nodes {
- canonicalName := n.Info.Name
- nFlat[canonicalName] += n.FlatValue()
- nCum[canonicalName] += n.CumValue()
- }
-
// Process graph and build various node and edge maps which will
// be consumed by AST walk.
+ weight := make(map[NamedCallEdge]int64)
for _, n := range g.Nodes {
seenStartLine = seenStartLine || n.Info.StartLine != 0
- p.TotalNodeWeight += n.FlatValue()
canonicalName := n.Info.Name
// Create the key to the nodeMapKey.
- nodeinfo := NodeMapKey{
+ namedEdge := NamedCallEdge{
CallerName: canonicalName,
CallSiteOffset: n.Info.Lineno - n.Info.StartLine,
}
for _, e := range n.Out {
- p.TotalEdgeWeight += e.WeightValue()
- nodeinfo.CalleeName = e.Dest.Info.Name
- if w, ok := p.NodeMap[nodeinfo]; ok {
- w.EWeight += e.WeightValue()
- } else {
- weights := new(Weights)
- weights.NFlat = nFlat[canonicalName]
- weights.NCum = nCum[canonicalName]
- weights.EWeight = e.WeightValue()
- p.NodeMap[nodeinfo] = weights
- }
+ totalWeight += e.WeightValue()
+ namedEdge.CalleeName = e.Dest.Info.Name
+ // Create new entry or increment existing entry.
+ weight[namedEdge] += e.WeightValue()
}
}
- if p.TotalNodeWeight == 0 || p.TotalEdgeWeight == 0 {
- return nil // accept but ignore profile with no samples.
+ if totalWeight == 0 {
+ return NamedEdgeMap{}, 0, nil // accept but ignore profile with no samples.
}
if !seenStartLine {
// TODO(prattmic): If Function.start_line is missing we could
// fall back to using absolute line numbers, which is better
// than nothing.
- return fmt.Errorf("profile missing Function.start_line data (Go version of profiled application too old? Go 1.20+ automatically adds this to profiles)")
+ return NamedEdgeMap{}, 0, fmt.Errorf("profile missing Function.start_line data (Go version of profiled application too old? Go 1.20+ automatically adds this to profiles)")
}
- return nil
+ byWeight := make([]NamedCallEdge, 0, len(weight))
+ for namedEdge := range weight {
+ byWeight = append(byWeight, namedEdge)
+ }
+ sort.Slice(byWeight, func(i, j int) bool {
+ ei, ej := byWeight[i], byWeight[j]
+ if wi, wj := weight[ei], weight[ej]; wi != wj {
+ return wi > wj // want larger weight first
+ }
+ // same weight, order by name/line number
+ if ei.CallerName != ej.CallerName {
+ return ei.CallerName < ej.CallerName
+ }
+ if ei.CalleeName != ej.CalleeName {
+ return ei.CalleeName < ej.CalleeName
+ }
+ return ei.CallSiteOffset < ej.CallSiteOffset
+ })
+
+ edgeMap = NamedEdgeMap{
+ Weight: weight,
+ ByWeight: byWeight,
+ }
+
+ return edgeMap, totalWeight, nil
}
// initializeIRGraph builds the IRGraph by visiting all the ir.Func in decl list
// of a package.
-func (p *Profile) initializeIRGraph() {
+func createIRGraph(namedEdgeMap NamedEdgeMap) *IRGraph {
+ g := &IRGraph{
+ IRNodes: make(map[string]*IRNode),
+ }
+
// Bottomup walk over the function to create IRGraph.
ir.VisitFuncsBottomUp(typecheck.Target.Funcs, func(list []*ir.Func, recursive bool) {
for _, fn := range list {
- p.VisitIR(fn)
+ visitIR(fn, namedEdgeMap, g)
}
})
// that IRNodes is fully populated (see the dummy node TODO in
// addIndirectEdges).
//
- // TODO(prattmic): VisitIR above populates the graph via direct calls
+ // TODO(prattmic): visitIR above populates the graph via direct calls
// discovered via the IR. addIndirectEdges populates the graph via
// calls discovered via the profile. This combination of opposite
// approaches is a bit awkward, particularly because direct calls are
// discoverable via the profile as well. Unify these into a single
// approach.
- p.addIndirectEdges()
-}
+ addIndirectEdges(g, namedEdgeMap)
-// VisitIR traverses the body of each ir.Func and use NodeMap to determine if
-// we need to add an edge from ir.Func and any node in the ir.Func body.
-func (p *Profile) VisitIR(fn *ir.Func) {
- g := p.WeightedCG
-
- if g.IRNodes == nil {
- g.IRNodes = make(map[string]*IRNode)
- }
+ return g
+}
+// visitIR traverses the body of each ir.Func adds edges to g from ir.Func to
+// any called function in the body.
+func visitIR(fn *ir.Func, namedEdgeMap NamedEdgeMap, g *IRGraph) {
name := ir.LinkFuncName(fn)
node, ok := g.IRNodes[name]
if !ok {
}
// Recursively walk over the body of the function to create IRGraph edges.
- p.createIRGraphEdge(fn, node, name)
+ createIRGraphEdge(fn, node, name, namedEdgeMap, g)
+}
+
+// createIRGraphEdge traverses the nodes in the body of ir.Func and adds edges
+// between the callernode which points to the ir.Func and the nodes in the
+// body.
+func createIRGraphEdge(fn *ir.Func, callernode *IRNode, name string, namedEdgeMap NamedEdgeMap, g *IRGraph) {
+ ir.VisitList(fn.Body, func(n ir.Node) {
+ switch n.Op() {
+ case ir.OCALLFUNC:
+ call := n.(*ir.CallExpr)
+ // Find the callee function from the call site and add the edge.
+ callee := DirectCallee(call.Fun)
+ if callee != nil {
+ addIREdge(callernode, name, n, callee, namedEdgeMap, g)
+ }
+ case ir.OCALLMETH:
+ call := n.(*ir.CallExpr)
+ // Find the callee method from the call site and add the edge.
+ callee := ir.MethodExprName(call.Fun).Func
+ addIREdge(callernode, name, n, callee, namedEdgeMap, g)
+ }
+ })
}
// NodeLineOffset returns the line offset of n in fn.
// addIREdge adds an edge between caller and new node that points to `callee`
// based on the profile-graph and NodeMap.
-func (p *Profile) addIREdge(callerNode *IRNode, callerName string, call ir.Node, callee *ir.Func) {
- g := p.WeightedCG
-
+func addIREdge(callerNode *IRNode, callerName string, call ir.Node, callee *ir.Func, namedEdgeMap NamedEdgeMap, g *IRGraph) {
calleeName := ir.LinkFuncName(callee)
calleeNode, ok := g.IRNodes[calleeName]
if !ok {
g.IRNodes[calleeName] = calleeNode
}
- nodeinfo := NodeMapKey{
+ namedEdge := NamedCallEdge{
CallerName: callerName,
CalleeName: calleeName,
CallSiteOffset: NodeLineOffset(call, callerNode.AST),
}
- var weight int64
- if weights, ok := p.NodeMap[nodeinfo]; ok {
- weight = weights.EWeight
- }
-
// Add edge in the IRGraph from caller to callee.
edge := &IREdge{
Src: callerNode,
Dst: calleeNode,
- Weight: weight,
- CallSiteOffset: nodeinfo.CallSiteOffset,
+ Weight: namedEdgeMap.Weight[namedEdge],
+ CallSiteOffset: namedEdge.CallSiteOffset,
}
if callerNode.OutEdges == nil {
- callerNode.OutEdges = make(map[NodeMapKey]*IREdge)
+ callerNode.OutEdges = make(map[NamedCallEdge]*IREdge)
}
- callerNode.OutEdges[nodeinfo] = edge
+ callerNode.OutEdges[namedEdge] = edge
+}
+
+// LookupFunc looks up a function or method in export data. It is expected to
+// be overridden by package noder, to break a dependency cycle.
+var LookupFunc = func(fullName string) (*ir.Func, error) {
+ base.Fatalf("pgo.LookupMethodFunc not overridden")
+ panic("unreachable")
}
// addIndirectEdges adds indirect call edges found in the profile to the graph,
// to be used for devirtualization.
//
-// targetDeclFuncs is the set of functions in typecheck.Target.Decls. Only
-// edges from these functions will be added.
-//
-// Devirtualization is only applied to typecheck.Target.Decls functions, so there
-// is no need to add edges from other functions.
-//
// N.B. despite the name, addIndirectEdges will add any edges discovered via
// the profile. We don't know for sure that they are indirect, but assume they
// are since direct calls would already be added. (e.g., direct calls that have
// TODO(prattmic): Devirtualization runs before inlining, so we can't devirtualize
// calls inside inlined call bodies. If we did add that, we'd need edges from
// inlined bodies as well.
-func (p *Profile) addIndirectEdges() {
- g := p.WeightedCG
-
+func addIndirectEdges(g *IRGraph, namedEdgeMap NamedEdgeMap) {
// g.IRNodes is populated with the set of functions in the local
// package build by VisitIR. We want to filter for local functions
// below, but we also add unknown callees to IRNodes as we go. So make
localNodes[k] = v
}
- for key, weights := range p.NodeMap {
+ // N.B. We must consider edges in a stable order because export data
+ // lookup order (LookupMethodFunc, below) can impact the export data of
+ // this package, which must be stable across different invocations for
+ // reproducibility.
+ //
+ // The weight ordering of ByWeight is irrelevant, it just happens to be
+ // an ordered list of edges that is already available.
+ for _, key := range namedEdgeMap.ByWeight {
+ weight := namedEdgeMap.Weight[key]
// All callers in the local package build were added to IRNodes
// in VisitIR. If a caller isn't in the local package build we
// can skip adding edges, since we won't be devirtualizing in
calleeNode, ok := g.IRNodes[key.CalleeName]
if !ok {
- // IR is missing for this callee. Most likely this is
- // because the callee isn't in the transitive deps of
- // this package.
+ // IR is missing for this callee. VisitIR populates
+ // IRNodes with all functions discovered via local
+ // package function declarations and calls. This
+ // function may still be available from export data of
+ // a transitive dependency.
//
- // Record this call anyway. If this is the hottest,
- // then we want to skip devirtualization rather than
- // devirtualizing to the second most common callee.
+ // TODO(prattmic): Parameterized types/functions are
+ // not supported.
//
- // TODO(prattmic): VisitIR populates IRNodes with all
- // of the functions discovered via local package
- // function declarations and calls. Thus we could miss
- // functions that are available in export data of
- // transitive deps, but aren't directly reachable. We
- // need to do a lookup directly from package export
- // data to get complete coverage.
- calleeNode = &IRNode{
- LinkerSymbolName: key.CalleeName,
- // TODO: weights? We don't need them.
+ // TODO(prattmic): This eager lookup during graph load
+ // is simple, but wasteful. We are likely to load many
+ // functions that we never need. We could delay load
+ // until we actually need the method in
+ // devirtualization. Instantiation of generic functions
+ // will likely need to be done at the devirtualization
+ // site, if at all.
+ fn, err := LookupFunc(key.CalleeName)
+ if err == nil {
+ if base.Debug.PGODebug >= 3 {
+ fmt.Printf("addIndirectEdges: %s found in export data\n", key.CalleeName)
+ }
+ calleeNode = &IRNode{AST: fn}
+
+ // N.B. we could call createIRGraphEdge to add
+ // direct calls in this newly-imported
+ // function's body to the graph. Similarly, we
+ // could add to this function's queue to add
+ // indirect calls. However, those would be
+ // useless given the visit order of inlining,
+ // and the ordering of PGO devirtualization and
+ // inlining. This function can only be used as
+ // an inlined body. We will never do PGO
+ // devirtualization inside an inlined call. Nor
+ // will we perform inlining inside an inlined
+ // call.
+ } else {
+ // Still not found. Most likely this is because
+ // the callee isn't in the transitive deps of
+ // this package.
+ //
+ // Record this call anyway. If this is the hottest,
+ // then we want to skip devirtualization rather than
+ // devirtualizing to the second most common callee.
+ if base.Debug.PGODebug >= 3 {
+ fmt.Printf("addIndirectEdges: %s not found in export data: %v\n", key.CalleeName, err)
+ }
+ calleeNode = &IRNode{LinkerSymbolName: key.CalleeName}
}
+
// Add dummy node back to IRNodes. We don't need this
// directly, but PrintWeightedCallGraphDOT uses these
// to print nodes.
edge := &IREdge{
Src: callerNode,
Dst: calleeNode,
- Weight: weights.EWeight,
+ Weight: weight,
CallSiteOffset: key.CallSiteOffset,
}
if callerNode.OutEdges == nil {
- callerNode.OutEdges = make(map[NodeMapKey]*IREdge)
+ callerNode.OutEdges = make(map[NamedCallEdge]*IREdge)
}
callerNode.OutEdges[key] = edge
}
}
-// createIRGraphEdge traverses the nodes in the body of ir.Func and adds edges
-// between the callernode which points to the ir.Func and the nodes in the
-// body.
-func (p *Profile) createIRGraphEdge(fn *ir.Func, callernode *IRNode, name string) {
- ir.VisitList(fn.Body, func(n ir.Node) {
- switch n.Op() {
- case ir.OCALLFUNC:
- call := n.(*ir.CallExpr)
- // Find the callee function from the call site and add the edge.
- callee := DirectCallee(call.X)
- if callee != nil {
- p.addIREdge(callernode, name, n, callee)
- }
- case ir.OCALLMETH:
- call := n.(*ir.CallExpr)
- // Find the callee method from the call site and add the edge.
- callee := ir.MethodExprName(call.X).Func
- p.addIREdge(callernode, name, n, callee)
- }
- })
-}
-
// WeightInPercentage converts profile weights to a percentage.
func WeightInPercentage(value int64, total int64) float64 {
return (float64(value) / float64(total)) * 100
style = "dashed"
}
color := "black"
- edgepercent := WeightInPercentage(e.Weight, p.TotalEdgeWeight)
+ edgepercent := WeightInPercentage(e.Weight, p.TotalWeight)
if edgepercent > edgeThreshold {
color = "red"
}