go/types: use internal/lazyregexp for goVersionRx

With benchinit, we see a noticeable improvement in init times:

	name     old time/op    new time/op    delta
	GoTypes    83.4µs ± 0%    43.7µs ± 1%  -47.57%  (p=0.029 n=4+4)

	name     old alloc/op   new alloc/op   delta
	GoTypes    26.5kB ± 0%    18.8kB ± 0%  -29.15%  (p=0.029 n=4+4)

	name     old allocs/op  new allocs/op  delta
	GoTypes       238 ± 0%       154 ± 0%  -35.29%  (p=0.029 n=4+4)

Port the same change to cmd/compile/internal/types and types2.

Updates #26775.

Change-Id: Ia1f7c4a4ce9a22d66e2aa9c9b9c341036993adca
Reviewed-on: https://go-review.googlesource.com/c/go/+/460544
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>
Run-TryBot: Robert Findley <rfindley@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>

src/cmd/compile/internal/types/goversion.go

@@ -7,8 +7,8 @@ package types
 import (
 	"fmt"
 	"internal/goversion"
+	"internal/lazyregexp"
 	"log"
-	"regexp"
 	"strconv"
 
 	"cmd/compile/internal/base"
@@ -81,4 +81,4 @@ func currentLang() string {
 
 // goVersionRE is a regular expression that matches the valid
 // arguments to the -lang flag.
-var goVersionRE = regexp.MustCompile(`^go([1-9]\d*)\.(0|[1-9]\d*)$`)
+var goVersionRE = lazyregexp.New(`^go([1-9]\d*)\.(0|[1-9]\d*)$`)

src/cmd/compile/internal/types2/version.go

@@ -7,7 +7,7 @@ package types2
 import (
 	"cmd/compile/internal/syntax"
 	"fmt"
-	"regexp"
+	"internal/lazyregexp"
 	"strconv"
 	"strings"
 )
@@ -78,4 +78,4 @@ func parseGoVersion(s string) (v version, err error) {
 }
 
 // goVersionRx matches a Go version string, e.g. "go1.12".
-var goVersionRx = regexp.MustCompile(`^go([1-9][0-9]*)\.(0|[1-9][0-9]*)$`)
+var goVersionRx = lazyregexp.New(`^go([1-9][0-9]*)\.(0|[1-9][0-9]*)$`)

src/go/build/deps_test.go

@@ -278,7 +278,7 @@ var depsRules = `
 	math/big, go/token
 	< go/constant;
 
-	container/heap, go/constant, go/parser, internal/types/errors, regexp
+	container/heap, go/constant, go/parser, internal/types/errors, internal/lazyregexp
 	< go/types;
 
 	FMT, internal/goexperiment

src/go/types/version.go

@@ -8,8 +8,8 @@ import (
 	"fmt"
 	"go/ast"
 	"go/token"
+	"internal/lazyregexp"
 	. "internal/types/errors"
-	"regexp"
 	"strconv"
 	"strings"
 )
@@ -80,4 +80,4 @@ func parseGoVersion(s string) (v version, err error) {
 }
 
 // goVersionRx matches a Go version string, e.g. "go1.12".
-var goVersionRx = regexp.MustCompile(`^go([1-9]\d*)\.(0|[1-9]\d*)$`)
+var goVersionRx = lazyregexp.New(`^go([1-9]\d*)\.(0|[1-9]\d*)$`)