cmd/compile/internal/pgo: readability refactor

Construction of Profile is getting more complex. Currently, we construct
a partial Profile and then use methods to slowly complete the structure.
This can hide dependencies and make refactoring fragile as the
requirements and outputs of the methods is not clearly specified.

Refactor construction to build the Profile only once all of the parts
are complete. The intermediate states explicitly pass input and outputs
as arguments.

Additionally, rename Profile.NodeMap to NamedEdgeMap to make its
contents more clear (edges, specified by caller/callee name rather than
IR). Remove the node flat/cumulative weight from this map; they are
unused.

Change-Id: I2079cd991daac6398d74375b04dfe120b473d908
Reviewed-on: https://go-review.googlesource.com/c/go/+/529558
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Cherry Mui <[email protected]>

Author: prattmic

src/cmd/compile/internal/inline/inl.go

@@ -86,7 +86,7 @@ func pgoInlinePrologue(p *pgo.Profile, funcs []*ir.Func) {
 			base.Fatalf("invalid PGOInlineCDFThreshold, must be between 0 and 100")
 		}
 	}
-	var hotCallsites []pgo.NodeMapKey
+	var hotCallsites []pgo.NamedCallEdge
 	inlineHotCallSiteThresholdPercent, hotCallsites = hotNodesFromCDF(p)
 	if base.Debug.PGODebug > 0 {
 		fmt.Printf("hot-callsite-thres-from-CDF=%v\n", inlineHotCallSiteThresholdPercent)
@@ -120,19 +120,19 @@ func pgoInlinePrologue(p *pgo.Profile, funcs []*ir.Func) {
 // (currently only used in debug prints) (in case of equal weights,
 // comparing with the threshold may not accurately reflect which nodes are
 // considiered hot).
-func hotNodesFromCDF(p *pgo.Profile) (float64, []pgo.NodeMapKey) {
+func hotNodesFromCDF(p *pgo.Profile) (float64, []pgo.NamedCallEdge) {
 	cum := int64(0)
-	for i, n := range p.NodesByWeight {
-		w := p.NodeMap[n].EWeight
+	for i, n := range p.NamedEdgeMap.ByWeight {
+		w := p.NamedEdgeMap.Weight[n]
 		cum += w
-		if pgo.WeightInPercentage(cum, p.TotalEdgeWeight) > inlineCDFHotCallSiteThresholdPercent {
+		if pgo.WeightInPercentage(cum, p.TotalWeight) > inlineCDFHotCallSiteThresholdPercent {
 			// nodes[:i+1] to include the very last node that makes it to go over the threshold.
 			// (Say, if the CDF threshold is 50% and one hot node takes 60% of weight, we want to
 			// include that node instead of excluding it.)
-			return pgo.WeightInPercentage(w, p.TotalEdgeWeight), p.NodesByWeight[:i+1]
+			return pgo.WeightInPercentage(w, p.TotalWeight), p.NamedEdgeMap.ByWeight[:i+1]
 		}
 	}
-	return 0, p.NodesByWeight
+	return 0, p.NamedEdgeMap.ByWeight
 }
 
 // InlinePackage finds functions that can be inlined and clones them before walk expands them.