cmd/compile: cleanup compile function

Make more idiomatic with a defer cleanup, which allows declaring
variables closer to their first use, rather than up front before the
first goto statement.

Also, split the legacy code generation code path into a separate
genlegacy function, analogous to the new genssa.

Passes toolstash -cmp.

Change-Id: I86c22838704f6861b75716ae64ba103b0e73b12f
Reviewed-on: https://go-review.googlesource.com/20353
Reviewed-by: Dave Cheney <dave@cheney.net>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

diff --git a/src/cmd/compile/internal/gc/pgen.go b/src/cmd/compile/internal/gc/pgen.go
index 37a0b2d4409844abc5f7291ee0982c83aa0e190c..26c276555bc28330e4bbea457ac1ee350f8a8b1a 100644 (file)
--- a/src/cmd/compile/internal/gc/pgen.go
+++ b/src/cmd/compile/internal/gc/pgen.go
@@ -350,31 +350,24 @@ func compile(fn *Node) {
                panicdottype = Sysfunc("panicdottype")
        }
 
-       lno := setlineno(fn)
+       defer func(lno int32) {
+               lineno = lno
+       }(setlineno(fn))
 
        Curfn = fn
        dowidth(Curfn.Type)
 
-       var nod1 Node
-       var ptxt *obj.Prog
-       var pl *obj.Plist
-       var p *obj.Prog
-       var n *Node
-       var nam *Node
-       var gcargs *Sym
-       var gclocals *Sym
-       var ssafn *ssa.Func
        if len(fn.Nbody.Slice()) == 0 {
                if pure_go != 0 || strings.HasPrefix(fn.Func.Nname.Sym.Name, "init.") {
                        Yyerror("missing function body for %q", fn.Func.Nname.Sym.Name)
-                       goto ret
+                       return
                }
 
                if Debug['A'] != 0 {
-                       goto ret
+                       return
                }
                emitptrargsmap()
-               goto ret
+               return
        }
 
        saveerrors()
@@ -385,37 +378,34 @@ func compile(fn *Node) {
        if Curfn.Type.Outnamed {
                // add clearing of the output parameters
                var save Iter
-               t := Structfirst(&save, Getoutarg(Curfn.Type))
-
-               for t != nil {
+               for t := Structfirst(&save, Getoutarg(Curfn.Type)); t != nil; t = structnext(&save) {
                        if t.Nname != nil {
-                               n = Nod(OAS, t.Nname, nil)
+                               n := Nod(OAS, t.Nname, nil)
                                typecheck(&n, Etop)
                                Curfn.Nbody.Set(append([]*Node{n}, Curfn.Nbody.Slice()...))
                        }
-
-                       t = structnext(&save)
                }
        }
 
        order(Curfn)
        if nerrors != 0 {
-               goto ret
+               return
        }
 
        hasdefer = false
        walk(Curfn)
        if nerrors != 0 {
-               goto ret
+               return
        }
        if instrumenting {
                instrument(Curfn)
        }
        if nerrors != 0 {
-               goto ret
+               return
        }
 
        // Build an SSA backend function.
+       var ssafn *ssa.Func
        if shouldssa(Curfn) {
                ssafn = buildssa(Curfn)
        }
@@ -423,17 +413,18 @@ func compile(fn *Node) {
        continpc = nil
        breakpc = nil
 
-       pl = newplist()
+       pl := newplist()
        pl.Name = Linksym(Curfn.Func.Nname.Sym)
 
        setlineno(Curfn)
 
+       var nod1 Node
        Nodconst(&nod1, Types[TINT32], 0)
-       nam = Curfn.Func.Nname
+       nam := Curfn.Func.Nname
        if isblank(nam) {
                nam = nil
        }
-       ptxt = Thearch.Gins(obj.ATEXT, nam, &nod1)
+       ptxt := Thearch.Gins(obj.ATEXT, nam, &nod1)
        Afunclit(&ptxt.From, Curfn.Func.Nname)
        ptxt.From3 = new(obj.Addr)
        if fn.Func.Dupok {
@@ -455,7 +446,7 @@ func compile(fn *Node) {
        // Clumsy but important.
        // See test/recover.go for test cases and src/reflect/value.go
        // for the actual functions being considered.
-       if myimportpath != "" && myimportpath == "reflect" {
+       if myimportpath == "reflect" {
                if Curfn.Func.Nname.Sym.Name == "callReflect" || Curfn.Func.Nname.Sym.Name == "callMethod" {
                        ptxt.From3.Offset |= obj.WRAPPER
                }
@@ -463,8 +454,8 @@ func compile(fn *Node) {
 
        ginit()
 
-       gcargs = makefuncdatasym("gcargs·%d", obj.FUNCDATA_ArgsPointerMaps)
-       gclocals = makefuncdatasym("gclocals·%d", obj.FUNCDATA_LocalsPointerMaps)
+       gcargs := makefuncdatasym("gcargs·%d", obj.FUNCDATA_ArgsPointerMaps)
+       gclocals := makefuncdatasym("gclocals·%d", obj.FUNCDATA_LocalsPointerMaps)
 
        for _, t := range Curfn.Func.Fieldtrack {
                gtrack(tracksym(t))
@@ -477,7 +468,7 @@ func compile(fn *Node) {
                switch n.Class {
                case PAUTO, PPARAM, PPARAMOUT:
                        Nodconst(&nod1, Types[TUINTPTR], n.Type.Width)
-                       p = Thearch.Gins(obj.ATYPE, n, &nod1)
+                       p := Thearch.Gins(obj.ATYPE, n, &nod1)
                        p.From.Gotype = Linksym(ngotype(n))
                }
        }
@@ -485,14 +476,19 @@ func compile(fn *Node) {
        if ssafn != nil {
                genssa(ssafn, ptxt, gcargs, gclocals)
                ssafn.Free()
-               goto ret
+       } else {
+               genlegacy(ptxt, gcargs, gclocals)
        }
+}
+
+// genlegacy compiles Curfn using the legacy non-SSA code generator.
+func genlegacy(ptxt *obj.Prog, gcargs, gclocals *Sym) {
        Genlist(Curfn.Func.Enter)
        Genlist(Curfn.Nbody)
        gclean()
        checklabels()
        if nerrors != 0 {
-               goto ret
+               return
        }
        if Curfn.Func.Endlineno != 0 {
                lineno = Curfn.Func.Endlineno
@@ -517,7 +513,7 @@ func compile(fn *Node) {
 
        gclean()
        if nerrors != 0 {
-               goto ret
+               return
        }
 
        Pc.As = obj.ARET // overwrite AEND
@@ -536,7 +532,7 @@ func compile(fn *Node) {
        setlineno(Curfn)
        if Stksize+Maxarg > 1<<31 {
                Yyerror("stack frame too large (>2GB)")
-               goto ret
+               return
        }
 
        // Emit garbage collection symbols.
@@ -553,7 +549,4 @@ func compile(fn *Node) {
 
        // Remove leftover instrumentation from the instruction stream.
        removevardef(ptxt)
-
-ret:
-       lineno = lno
 }