go.tools/go/pointer: add intrinsic for time.startTimer, which is implemented in C.

Without it, no value appears to be sent on NewTicker/NewTimer channels.

+ test

Also:
- add (callgraph.Edge).{Description,Pos} convenience methods
  to simplify client code when Site==nil.

LGTM=gri
R=gri, friestein68503
CC=golang-codereviews
https://golang.org/cl/112610043

go/callgraph/callgraph.go

@@ -41,6 +41,7 @@ package callgraph
 
 import (
 	"fmt"
+	"go/token"
 
 	"code.google.com/p/go.tools/go/ssa"
 )
@@ -99,6 +100,20 @@ func (e Edge) String() string {
 	return fmt.Sprintf("%s --> %s", e.Caller, e.Callee)
 }
 
+func (e Edge) Description() string {
+	if e.Site == nil {
+		return "synthetic call"
+	}
+	return e.Site.Common().Description()
+}
+
+func (e Edge) Pos() token.Pos {
+	if e.Site == nil {
+		return token.NoPos
+	}
+	return e.Site.Pos()
+}
+
 // AddEdge adds the edge (caller, site, callee) to the call graph.
 // Elimination of duplicate edges is the caller's responsibility.
 func AddEdge(caller *Node, site ssa.CallInstruction, callee *Node) {

go/pointer/intrinsics.go

@@ -174,7 +174,7 @@ func init() {
 		"syscall.setenv_c":                      ext۰NoEffect,
 		"time.Sleep":                            ext۰NoEffect,
 		"time.now":                              ext۰NoEffect,
-		"time.startTimer":                       ext۰NoEffect,
+		"time.startTimer":                       ext۰time۰startTimer,
 		"time.stopTimer":                        ext۰NoEffect,
 	} {
 		intrinsicsByName[name] = fn
@@ -243,12 +243,8 @@ func (a *analysis) isReflect(fn *ssa.Function) bool {
 func ext۰NoEffect(a *analysis, cgn *cgnode) {}
 
 func ext۰NotYetImplemented(a *analysis, cgn *cgnode) {
-	// TODO(adonovan): enable this warning when we've implemented
+	fn := cgn.fn
-	// enough that it's not unbearably annoying.
+	a.warnf(fn.Pos(), "unsound: intrinsic treatment of %s not yet implemented", fn)
-	if true {
-		fn := cgn.fn
-		a.warnf(fn.Pos(), "unsound: intrinsic treatment of %s not yet implemented", fn)
-	}
 }
 
 // ---------- func runtime.SetFinalizer(x, f interface{}) ----------
@@ -320,3 +316,65 @@ func ext۰runtime۰SetFinalizer(a *analysis, cgn *cgnode) {
 		f:       params + 1,
 	})
 }
+
+// ---------- func time.startTimer(t *runtimeTimer) ----------
+
+// time.StartTimer(t)
+type timeStartTimerConstraint struct {
+	targets nodeid // (indirect)
+	t       nodeid // (ptr)
+}
+
+func (c *timeStartTimerConstraint) ptr() nodeid { return c.t }
+func (c *timeStartTimerConstraint) presolve(h *hvn) {
+	h.markIndirect(onodeid(c.targets), "StartTimer.targets")
+}
+func (c *timeStartTimerConstraint) renumber(mapping []nodeid) {
+	c.targets = mapping[c.targets]
+	c.t = mapping[c.t]
+}
+
+func (c *timeStartTimerConstraint) String() string {
+	return fmt.Sprintf("time.startTimer(n%d)", c.t)
+}
+
+func (c *timeStartTimerConstraint) solve(a *analysis, delta *nodeset) {
+	for _, tObj := range delta.AppendTo(a.deltaSpace) {
+		t := nodeid(tObj)
+
+		// We model startTimer as if it was defined thus:
+		// 	func startTimer(t *runtimeTimer) { t.f(0, t.arg) }
+
+		// We hard-code the field offsets of time.runtimeTimer:
+		// type runtimeTimer struct {
+		//  0     __identity__
+		//  1    i      int32
+		//  2    when   int64
+		//  3    period int64
+		//  4    f      func(int64, interface{})
+		//  5    arg    interface{}
+		// }
+		f := t + 4
+		arg := t + 5
+
+		// store t.arg to t.f.params[1]
+		// (offset 2 => skip identity and int64 param)
+		a.store(f, arg, 2, 1)
+
+		// Add dynamic call target.
+		if a.onlineCopy(c.targets, f) {
+			a.addWork(c.targets)
+		}
+	}
+}
+
+func ext۰time۰startTimer(a *analysis, cgn *cgnode) {
+	// This is the shared contour, used for dynamic calls.
+	targets := a.addOneNode(tInvalid, "startTimer.targets", nil)
+	cgn.sites = append(cgn.sites, &callsite{targets: targets})
+	params := a.funcParams(cgn.obj)
+	a.addConstraint(&timeStartTimerConstraint{
+		targets: targets,
+		t:       params,
+	})
+}

go/pointer/pointer_test.go

@@ -54,6 +54,7 @@ var inputs = []string{
 	"testdata/rtti.go",
 	"testdata/structreflect.go",
 	"testdata/structs.go",
+	"testdata/timer.go",
 }
 
 // Expectation grammar:

godoc/analysis/callgraph.go

@@ -43,7 +43,7 @@ func (a *analysis) doCallgraph(cg *callgraph.Graph) {
 	for _, n := range cg.Nodes {
 		for _, e := range n.Out {
 			if e.Site == nil {
-				continue // a call from the <root> node
+				continue // a call from a synthetic node such as <root>
 			}
 
 			// Add (site pos, callee) to calledFuncs.

oracle/callers.go

@@ -63,25 +63,20 @@ func (r *callersResult) display(printf printfFunc) {
 			if edge.Caller == root {
 				printf(r.target, "the root of the call graph")
 			} else {
-				printf(edge.Site, "\t%s from %s", edge.Site.Common().Description(), edge.Caller.Func)
+				printf(edge, "\t%s from %s", edge.Description(), edge.Caller.Func)
 			}
 		}
 	}
 }
 
 func (r *callersResult) toSerial(res *serial.Result, fset *token.FileSet) {
-	root := r.callgraph.Root
 	var callers []serial.Caller
 	for _, edge := range r.edges {
-		var c serial.Caller
+		callers = append(callers, serial.Caller{
-		c.Caller = edge.Caller.Func.String()
+			Caller: edge.Caller.Func.String(),
-		if edge.Caller == root {
+			Pos:    fset.Position(edge.Pos()).String(),
-			c.Desc = "synthetic call"
+			Desc:   edge.Description(),
-		} else {
+		})
-			c.Pos = fset.Position(edge.Site.Pos()).String()
-			c.Desc = edge.Site.Common().Description()
-		}
-		callers = append(callers, c)
 	}
 	res.Callers = callers
 }

oracle/callstack.go

@@ -71,7 +71,7 @@ func (r *callstackResult) display(printf printfFunc) {
 		printf(r.target, "%s", r.target)
 		for i := len(r.callpath) - 1; i >= 0; i-- {
 			edge := r.callpath[i]
-			printf(edge.Site, "%s from %s", edge.Site.Common().Description(), edge.Caller.Func)
+			printf(edge, "%s from %s", edge.Description(), edge.Caller.Func)
 		}
 	} else {
 		printf(r.target, "%s is unreachable in this analysis scope", r.target)
@@ -83,9 +83,9 @@ func (r *callstackResult) toSerial(res *serial.Result, fset *token.FileSet) {
 	for i := len(r.callpath) - 1; i >= 0; i-- { // (innermost first)
 		edge := r.callpath[i]
 		callers = append(callers, serial.Caller{
-			Pos:    fset.Position(edge.Site.Pos()).String(),
+			Pos:    fset.Position(edge.Pos()).String(),
 			Caller: edge.Caller.Func.String(),
-			Desc:   edge.Site.Common().Description(),
+			Desc:   edge.Description(),
 		})
 	}
 	res.Callstack = &serial.CallStack{