cmd/internal/gc: add internConcat for alloc-free string concatenation

This is a follow-up to review comments on CL 7696.

I believe that this includes the first regular Go test in the compiler.

No functional changes. Passes toolstash -cmp.

Change-Id: Id45f51aa664c5d52ece2a61cd7d8417159ce3cf0
Reviewed-on: https://go-review.googlesource.com/7820
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

diff --git a/src/cmd/internal/gc/lex.go b/src/cmd/internal/gc/lex.go
index 7470a1ff3a1e38a64940d1217b875ac3c3690ed5..623c9a1d93e750d1954bb9a55b1dd8e51f3e5259 100644 (file)
--- a/src/cmd/internal/gc/lex.go
+++ b/src/cmd/internal/gc/lex.go
@@ -1511,6 +1511,15 @@ func internString(b []byte) string {
        return s
 }
 
+func internConcat(ss ...string) string {
+       const bufsiz = 128 // big enough for most compiler uses; must be constant to avoid heap alloc
+       b := make([]byte, 0, bufsiz)
+       for _, s := range ss {
+               b = append(b, s...)
+       }
+       return internString(b)
+}
+
 func more(pp *string) bool {
        p := *pp
        for p != "" && yy_isspace(int(p[0])) {

diff --git a/src/cmd/internal/gc/lex_test.go b/src/cmd/internal/gc/lex_test.go
new file mode 100644 (file)
index 0000000..845a9d8
--- /dev/null
+++ b/src/cmd/internal/gc/lex_test.go
@@ -0,0 +1,22 @@
+// Copyright 2015 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package gc
+
+import "testing"
+
+func TestInternConcat(t *testing.T) {
+       fromKind := "T"
+       toKind := "E"
+       var s string
+       n := testing.AllocsPerRun(100, func() {
+               s = internConcat("conv", fromKind, "2", toKind)
+       })
+       if s != "convT2E" {
+               t.Fatalf("internConcat(\"conv\", \"T\", \"2\", \"E\")=%q want %q", s, "convT2E")
+       }
+       if n > 0 {
+               t.Errorf("internConcat allocs per run=%f", n)
+       }
+}

diff --git a/src/cmd/internal/gc/subr.go b/src/cmd/internal/gc/subr.go
index 32486c77bb83a522761b5e87f8ab4ef64b21eba1..43aa382206b8f6002bc65ba490bdba54a84a6b64 100644 (file)
--- a/src/cmd/internal/gc/subr.go
+++ b/src/cmd/internal/gc/subr.go
@@ -3574,10 +3574,10 @@ func isdirectiface(t *Type) bool {
        return false
 }
 
-// type2IET returns "T" if t is a concrete type,
-// "I" if t is an interface type, and "E" if t is an empty interface type.
+// IET returns "T" if t is a concrete type, "I" if t is an interface type, and
+// "E" if t is an empty interface type.
 // It is used to build calls to the conv* and assert* runtime routines.
-func type2IET(t *Type) string {
+func (t *Type) IET() string {
        if isnilinter(t) {
                return "E"
        }

diff --git a/src/cmd/internal/gc/walk.go b/src/cmd/internal/gc/walk.go
index 2784648a858ae009d98a7f578920eb35e667b0fd..591974d18b218d1b1f2ad8f4d506dbbbb80ed77c 100644 (file)
--- a/src/cmd/internal/gc/walk.go
+++ b/src/cmd/internal/gc/walk.go
@@ -678,7 +678,7 @@ func walkexpr(np **Node, init **NodeList) {
                        n1 := Nod(OADDR, n.Left, nil)
                        r := n.Right // i.(T)
 
-                       buf := "assert" + type2IET(r.Left.Type) + "2" + type2IET(r.Type)
+                       buf := internConcat("assert", r.Left.Type.IET(), "2", r.Type.IET())
                        fn := syslook(buf, 1)
                        substArgTypes(fn, r.Left.Type, r.Type)
 
@@ -869,8 +869,8 @@ func walkexpr(np **Node, init **NodeList) {
                        oktype = ok.Type
                }
 
-               fromKind := type2IET(from.Type)
-               toKind := type2IET(t)
+               fromKind := from.Type.IET()
+               toKind := t.IET()
 
                // Avoid runtime calls in a few cases of the form _, ok := i.(T).
                // This is faster and shorter and allows the corresponding assertX2X2
@@ -903,7 +903,7 @@ func walkexpr(np **Node, init **NodeList) {
                }
                resptr.Etype = 1 // addr does not escape
 
-               buf := "assert" + fromKind + "2" + toKind + "2"
+               buf := internConcat("assert", fromKind, "2", toKind, "2")
                fn := syslook(buf, 1)
                substArgTypes(fn, from.Type, t)
                call := mkcall1(fn, oktype, init, typename(t), from, resptr)
@@ -927,11 +927,7 @@ func walkexpr(np **Node, init **NodeList) {
                        goto ret
                }
 
-               // Build name of function: convI2E etc.
-               // Not all names are possible
-               // (e.g., we'll never generate convE2E or convE2I).
-               buf := "conv" + type2IET(n.Left.Type) + "2" + type2IET(n.Type)
-               fn := syslook(buf, 1)
+               // Handle fast paths and special cases.
                var ll *NodeList
                if !Isinter(n.Left.Type) {
                        ll = list(ll, typename(n.Left.Type))
@@ -1010,6 +1006,11 @@ func walkexpr(np **Node, init **NodeList) {
                        }
                }
 
+               // Build name of function: convI2E etc.
+               // Not all names are possible
+               // (e.g., we'll never generate convE2E or convE2I).
+               buf := internConcat("conv", n.Left.Type.IET(), "2", n.Type.IET())
+               fn := syslook(buf, 1)
                substArgTypes(fn, n.Left.Type, n.Type)
                dowidth(fn.Type)
                n = Nod(OCALL, fn, nil)