cmd/compile: number autotmps per-func, not per-package

Prior to this CL, autotmps were global to a package.
They also shared numbering with static variables.
Switch autotmp numbering to be per-function instead,
and do implicit numbering based on len(Func.Dcl).
This eliminates a dependency on a global variable
from the backend without adding to the Func struct.
While we're here, move statuniqgen closer to its
sole remaining user.

This actually improves compiler performance,
because the autotmp_* names can now be
reused across functions.

name       old alloc/op    new alloc/op    delta
Template      40.6MB ± 0%     40.1MB ± 0%  -1.38%  (p=0.000 n=10+10)
Unicode       29.9MB ± 0%     29.9MB ± 0%    ~     (p=0.912 n=10+10)
GoTypes        116MB ± 0%      114MB ± 0%  -1.53%  (p=0.000 n=10+10)
SSA            865MB ± 0%      856MB ± 0%  -1.04%  (p=0.000 n=10+10)
Flate         25.8MB ± 0%     25.4MB ± 0%  -1.36%  (p=0.000 n=10+10)
GoParser      32.2MB ± 0%     32.0MB ± 0%  -0.72%  (p=0.000 n=10+10)
Reflect       80.3MB ± 0%     79.0MB ± 0%  -1.65%  (p=0.000 n=9+10)
Tar           27.0MB ± 0%     26.7MB ± 0%  -0.86%  (p=0.000 n=10+9)
XML           42.8MB ± 0%     42.4MB ± 0%  -0.95%  (p=0.000 n=10+10)

name       old allocs/op   new allocs/op   delta
Template        398k ± 1%       396k ± 1%  -0.59%  (p=0.002 n=10+10)
Unicode         321k ± 1%       321k ± 0%    ~     (p=0.912 n=10+10)
GoTypes        1.17M ± 0%      1.16M ± 0%  -0.77%  (p=0.000 n=10+10)
SSA            7.65M ± 0%      7.62M ± 0%  -0.40%  (p=0.000 n=10+10)
Flate           240k ± 1%       238k ± 1%  -0.56%  (p=0.001 n=10+10)
GoParser        323k ± 1%       320k ± 1%  -0.65%  (p=0.002 n=10+10)
Reflect        1.01M ± 0%      1.00M ± 0%  -0.37%  (p=0.001 n=9+10)
Tar             256k ± 1%       255k ± 0%    ~     (p=0.101 n=10+8)
XML             400k ± 1%       398k ± 1%    ~     (p=0.063 n=10+10)


Change-Id: I3c23ca98129137d373106990b1a3e1507bbe0cc3
Reviewed-on: https://go-review.googlesource.com/38729
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

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

@@ -10,6 +10,7 @@ import (
 	"cmd/internal/obj"
 	"cmd/internal/src"
 	"fmt"
+	"strconv"
 )
 
 func Sysfunc(name string) *obj.LSym {
@@ -182,6 +183,17 @@ func moveToHeap(n *Node) {
 	}
 }
 
+// autotmpname returns the name for an autotmp variable numbered n.
+func autotmpname(n int) string {
+	// Give each tmp a different name so that they can be registerized.
+	// Add a preceding . to avoid clashing with legal names.
+	const prefix = ".autotmp_"
+	// Start with a buffer big enough to hold a large n.
+	b := []byte(prefix + "      ")[:len(prefix)]
+	b = strconv.AppendInt(b, int64(n), 10)
+	return internString(b)
+}
+
 // make a new Node off the books
 func tempname(nn *Node, t *Type) {
 	if Curfn == nil {
@@ -191,16 +203,14 @@ func tempname(nn *Node, t *Type) {
 		Dump("tempname", Curfn)
 		Fatalf("adding tempname to wrong closure function")
 	}
-
 	if t == nil {
 		Fatalf("tempname called with nil type")
 	}
 
-	// give each tmp a different name so that there
-	// a chance to registerizer them.
-	// Add a preceding . to avoid clash with legal names.
-	s := lookupN(".autotmp_", statuniqgen)
-	statuniqgen++
+	s := &Sym{
+		Name: autotmpname(len(Curfn.Func.Dcl)),
+		Pkg:  localpkg,
+	}
 	n := newname(s)
 	s.Def = n
 	n.Type = t

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

@@ -242,8 +242,6 @@ var funcsyms []*Sym
 
 var dclcontext Class // PEXTERN/PAUTO
 
-var statuniqgen int // name generator for static temps
-
 var Curfn *Node
 
 var Widthptr int

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

@@ -569,6 +569,8 @@ const (
 // data statements for the constant
 // part of the composite literal.
 
+var statuniqgen int // name generator for static temps
+
 // staticname returns a name backed by a static data symbol.
 // Callers should call n.Name.SetReadonly(true) on the
 // returned node for readonly nodes.