cmd/compile: add flag for debugging PC-value tables

For example, `-d pctab=pctoinline` prints the PC-inline table and
inlining tree for every function.

Change-Id: Ia6b9ce4d83eed0b494318d40ffe06481ec5d58ab
Reviewed-on: https://go-review.googlesource.com/37235
Run-TryBot: David Lazar <lazard@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>

src/cmd/compile/internal/gc/main.go

@@ -37,6 +37,7 @@ var (
 	Debug_panic    int
 	Debug_slice    int
 	Debug_wb       int
+	Debug_pctab    string
 )
 
 // Debug arguments.
@@ -59,6 +60,7 @@ var debugtab = []struct {
 	{"typeassert", &Debug_typeassert}, // print information about type assertion inlining
 	{"wb", &Debug_wb},                 // print information about write barriers
 	{"export", &Debug_export},         // print export data
+	{"pctab", &Debug_pctab},           // print named pc-value table
 }
 
 func usage() {
@@ -319,6 +321,9 @@ func Main() {
 		}
 	}
 
+	// set via a -d flag
+	Ctxt.Debugpcln = Debug_pctab
+
 	// enable inlining.  for now:
 	//	default: inlining on.  (debug['l'] == 1)
 	//	-l: inlining off  (debug['l'] == 0)

src/cmd/internal/obj/inl.go

@@ -76,3 +76,10 @@ func (ctxt *Link) OutermostPos(xpos src.XPos) src.Pos {
 	}
 	return ctxt.PosTable.Pos(outerxpos)
 }
+
+func dumpInlTree(ctxt *Link, tree InlTree) {
+	for i, call := range tree.nodes {
+		pos := ctxt.PosTable.Pos(call.Pos)
+		ctxt.Logf("%0d | %0d | %s (%s)\n", i, call.Parent, call.Func, pos)
+	}
+}

src/cmd/internal/obj/link.go

@@ -716,7 +716,7 @@ type Link struct {
 	Debugasm      int32
 	Debugvlog     int32
 	Debugdivmod   int32
-	Debugpcln     int32
+	Debugpcln     string
 	Flag_shared   bool
 	Flag_dynlink  bool
 	Flag_optimize bool

src/cmd/internal/obj/pcln.go

@@ -24,31 +24,23 @@ func addvarint(d *Pcdata, v uint32) {
 // where func is the function, val is the current value, p is the instruction being
 // considered, and arg can be used to further parameterize valfunc.
 func funcpctab(ctxt *Link, dst *Pcdata, func_ *LSym, desc string, valfunc func(*Link, *LSym, int32, *Prog, int32, interface{}) int32, arg interface{}) {
-	// To debug a specific function, uncomment lines and change name.
+	dbg := desc == ctxt.Debugpcln
-	dbg := 0
-
-	//if func_.Name == "main.main" || desc == "pctospadj" {
-	//	dbg = 1
-	//}
-
-	ctxt.Debugpcln += int32(dbg)
 
 	dst.P = dst.P[:0]
 
-	if ctxt.Debugpcln != 0 {
+	if dbg {
 		ctxt.Logf("funcpctab %s [valfunc=%s]\n", func_.Name, desc)
 	}
 
 	val := int32(-1)
 	oldval := val
 	if func_.Text == nil {
-		ctxt.Debugpcln -= int32(dbg)
 		return
 	}
 
 	pc := func_.Text.Pc
 
-	if ctxt.Debugpcln != 0 {
+	if dbg {
 		ctxt.Logf("%6x %6d %v\n", uint64(pc), val, func_.Text)
 	}
 
@@ -60,7 +52,7 @@ func funcpctab(ctxt *Link, dst *Pcdata, func_ *LSym, desc string, valfunc func(*
 
 		if val == oldval && started != 0 {
 			val = valfunc(ctxt, func_, val, p, 1, arg)
-			if ctxt.Debugpcln != 0 {
+			if dbg {
 				ctxt.Logf("%6x %6s %v\n", uint64(p.Pc), "", p)
 			}
 			continue
@@ -72,7 +64,7 @@ func funcpctab(ctxt *Link, dst *Pcdata, func_ *LSym, desc string, valfunc func(*
 		// for a true instruction boundary in the program.
 		if p.Link != nil && p.Link.Pc == p.Pc {
 			val = valfunc(ctxt, func_, val, p, 1, arg)
-			if ctxt.Debugpcln != 0 {
+			if dbg {
 				ctxt.Logf("%6x %6s %v\n", uint64(p.Pc), "", p)
 			}
 			continue
@@ -92,7 +84,7 @@ func funcpctab(ctxt *Link, dst *Pcdata, func_ *LSym, desc string, valfunc func(*
 		// as variable-length little-endian base-128 integers,
 		// where the 0x80 bit indicates that the integer continues.
 
-		if ctxt.Debugpcln != 0 {
+		if dbg {
 			ctxt.Logf("%6x %6d %v\n", uint64(p.Pc), val, p)
 		}
 
@@ -114,22 +106,20 @@ func funcpctab(ctxt *Link, dst *Pcdata, func_ *LSym, desc string, valfunc func(*
 	}
 
 	if started != 0 {
-		if ctxt.Debugpcln != 0 {
+		if dbg {
 			ctxt.Logf("%6x done\n", uint64(func_.Text.Pc+func_.Size))
 		}
 		addvarint(dst, uint32((func_.Size-pc)/int64(ctxt.Arch.MinLC)))
 		addvarint(dst, 0) // terminator
 	}
 
-	if ctxt.Debugpcln != 0 {
+	if dbg {
 		ctxt.Logf("wrote %d bytes to %p\n", len(dst.P), dst)
 		for i := 0; i < len(dst.P); i++ {
 			ctxt.Logf(" %02x", dst.P[i])
 		}
 		ctxt.Logf("\n")
 	}
-
-	ctxt.Debugpcln -= int32(dbg)
 }
 
 // pctofileline computes either the file number (arg == 0)
@@ -297,6 +287,11 @@ func linkpcln(ctxt *Link, cursym *LSym) {
 	pcinlineState := new(pcinlineState)
 	funcpctab(ctxt, &pcln.Pcinline, cursym, "pctoinline", pcinlineState.pctoinline, nil)
 	pcln.InlTree = pcinlineState.localTree
+	if ctxt.Debugpcln == "pctoinline" && len(pcln.InlTree.nodes) > 0 {
+		ctxt.Logf("-- inlining tree for %s:\n", cursym)
+		dumpInlTree(ctxt, pcln.InlTree)
+		ctxt.Logf("--\n")
+	}
 
 	// tabulate which pc and func data we have.
 	havepc := make([]uint32, (npcdata+31)/32)