cmd/compile: remove makefuncdatasym_nsym global

This causes a minor reduction in allocations,
because the old funcdatasym names were
being interned unnecessarily.

Updates #15756

name       old alloc/op    new alloc/op    delta
Template      39.9MB ± 0%     39.9MB ± 0%    ~     (p=0.280 n=10+10)
Unicode       29.9MB ± 0%     29.8MB ± 0%  -0.26%  (p=0.000 n=10+10)
GoTypes        113MB ± 0%      113MB ± 0%  -0.12%  (p=0.000 n=10+10)
SSA            855MB ± 0%      855MB ± 0%  -0.03%  (p=0.001 n=10+10)
Flate         25.4MB ± 0%     25.3MB ± 0%  -0.30%  (p=0.000 n=10+10)
GoParser      31.9MB ± 0%     31.8MB ± 0%    ~     (p=0.065 n=10+9)
Reflect       78.4MB ± 0%     78.2MB ± 0%  -0.15%  (p=0.000 n=9+10)
Tar           26.7MB ± 0%     26.7MB ± 0%  -0.17%  (p=0.000 n=9+10)
XML           42.3MB ± 0%     42.4MB ± 0%  +0.07%  (p=0.011 n=10+10)

name       old allocs/op   new allocs/op   delta
Template        390k ± 0%       390k ± 0%    ~     (p=0.905 n=9+10)
Unicode         319k ± 1%       319k ± 1%    ~     (p=0.724 n=10+10)
GoTypes        1.14M ± 0%      1.14M ± 0%    ~     (p=0.393 n=10+10)
SSA            7.60M ± 0%      7.60M ± 0%    ~     (p=0.604 n=9+10)
Flate           235k ± 1%       234k ± 1%    ~     (p=0.105 n=10+10)
GoParser        317k ± 0%       316k ± 1%    ~     (p=0.280 n=10+10)
Reflect         979k ± 0%       979k ± 0%    ~     (p=0.315 n=10+10)
Tar             251k ± 0%       251k ± 1%    ~     (p=0.762 n=8+10)
XML             393k ± 0%       394k ± 1%    ~     (p=0.095 n=9+10)

name       old text-bytes  new text-bytes  delta
HelloSize       684k ± 0%       684k ± 0%    ~     (all equal)

name       old data-bytes  new data-bytes  delta
HelloSize       138k ± 0%       138k ± 0%    ~     (all equal)

name       old exe-bytes   new exe-bytes   delta
HelloSize      1.03M ± 0%      1.03M ± 0%    ~     (all equal)

Change-Id: Idba33da4e89c325984ac46e4852cf12e4a7fd1a9
Reviewed-on: https://go-review.googlesource.com/39032
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
Reviewed-by: Robert Griesemer <gri@golang.org>

src/cmd/compile/fmt_test.go

@@ -654,6 +654,7 @@ var knownFormats = map[string]string{
 	"cmd/compile/internal/syntax.token %s":            "",
 	"cmd/internal/src.Pos %s":                         "",
 	"cmd/internal/src.Pos %v":                         "",
+	"cmd/internal/src.XPos %v":                        "",
 	"error %v":                                        "",
 	"float64 %.2f":                                    "",
 	"float64 %.3f":                                    "",

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

@@ -16,11 +16,31 @@ import (
 
 // "Portable" code generation.
 
-var makefuncdatasym_nsym int
+func makefuncdatasym(pp *Progs, nameprefix string, funcdatakind int64, curfn *Node) *Sym {
+	// This symbol requires a unique, reproducible name;
+	// unique to avoid duplicate symbols,
+	// and reproducible for reproducible builds and toolstash.
+	// The function name will usually suffice.
+	suffix := curfn.Func.Nname.Sym.Name
+	if suffix == "_" {
+		// It is possible to have multiple functions called _,
+		// so in this rare case, use instead the function's position.
+		// This formatted string will be meaningless gibberish, but that's ok.
+		// It will be unique and reproducible, and it is rare anyway.
+		// Note that we can't just always use the position;
+		// it is possible to have multiple autogenerated functions at the same position.
+		// Fortunately, no autogenerated functions are called _.
+		if curfn.Pos == autogeneratedPos {
+			Fatalf("autogenerated func _")
+		}
+		suffix = fmt.Sprintf("%v", curfn.Pos)
+	}
+	// Add in the package path as well.
+	// When generating wrappers, we can end up compiling a function belonging
+	// to other packages, which might have a name that collides with one in our package.
+	symname := nameprefix + curfn.Func.Nname.Sym.Pkg.Path + "." + suffix
 
-func makefuncdatasym(pp *Progs, nameprefix string, funcdatakind int64) *Sym {
-	sym := lookupN(nameprefix, makefuncdatasym_nsym)
-	makefuncdatasym_nsym++
+	sym := lookup(symname)
 	p := pp.Prog(obj.AFUNCDATA)
 	Addrconst(&p.From, funcdatakind)
 	p.To.Type = obj.TYPE_MEM

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

@@ -4274,8 +4274,8 @@ func genssa(f *ssa.Func, pp *Progs) {
 	e := f.Frontend().(*ssafn)
 
 	// Generate GC bitmaps.
-	gcargs := makefuncdatasym(pp, "gcargs·", obj.FUNCDATA_ArgsPointerMaps)
-	gclocals := makefuncdatasym(pp, "gclocals·", obj.FUNCDATA_LocalsPointerMaps)
+	gcargs := makefuncdatasym(pp, "gcargs·", obj.FUNCDATA_ArgsPointerMaps, e.curfn)
+	gclocals := makefuncdatasym(pp, "gclocals·", obj.FUNCDATA_LocalsPointerMaps, e.curfn)
 	s.stackMapIndex = liveness(e, f, gcargs, gclocals)
 
 	// Remember where each block starts.