[dev.simd] simd, cmd/compile, go build, go/doc: test tweaks

these are for CL 675618
simd package exists and imports internal/cpu
tweak tests to deal with goexperiment/not

Change-Id: I2de99d048f0a228d5f3cd750c39ee5925107556e
Reviewed-on: https://go-review.googlesource.com/c/go/+/677260
Reviewed-by: Junyang Shao <shaojunyang@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Junyang Shao <shaojunyang@google.com>

src/cmd/compile/internal/ssagen/intrinsics_test.go

@@ -7,6 +7,7 @@ package ssagen
 import (
 	"flag"
 	"fmt"
+	"internal/buildcfg"
 	"slices"
 	"strings"
 	"testing"
@@ -15,6 +16,7 @@ import (
 )
 
 var updateIntrinsics = flag.Bool("update", false, "Print an updated intrinsics table")
+var simd = flag.Bool("simd", buildcfg.Experiment.SIMD, "Also check SIMD intrinsics; defaults to GOEXPERIMENT==simd")
 
 type testIntrinsicKey struct {
 	archName string
@@ -1375,13 +1377,13 @@ func TestIntrinsics(t *testing.T) {
 		gotIntrinsics[testIntrinsicKey{ik.arch.Name, ik.pkg, ik.fn}] = struct{}{}
 	}
 	for ik, _ := range gotIntrinsics {
-		if _, found := wantIntrinsics[ik]; !found {
+		if _, found := wantIntrinsics[ik]; !found && (ik.pkg != "simd" || *simd) {
 			t.Errorf("Got unwanted intrinsic %v %v.%v", ik.archName, ik.pkg, ik.fn)
 		}
 	}
 
 	for ik, _ := range wantIntrinsics {
-		if _, found := gotIntrinsics[ik]; !found {
+		if _, found := gotIntrinsics[ik]; !found && (ik.pkg != "simd" || *simd) {
 			t.Errorf("Want missing intrinsic %v %v.%v", ik.archName, ik.pkg, ik.fn)
 		}
 	}

src/go/build/deps_test.go

@@ -70,6 +70,8 @@ var depsRules = `
 	internal/goarch < internal/abi;
 	internal/byteorder, internal/cpu, internal/goarch < internal/chacha8rand;
 
+	internal/cpu < simd;
+
 	# RUNTIME is the core runtime group of packages, all of them very light-weight.
 	internal/abi,
 	internal/chacha8rand,

src/go/doc/comment/std.go

@@ -35,6 +35,7 @@ var stdPkgs = []string{
 	"reflect",
 	"regexp",
 	"runtime",
+	"simd",
 	"slices",
 	"sort",
 	"strconv",

src/go/doc/comment/std_test.go

@@ -5,6 +5,7 @@
 package comment
 
 import (
+	"internal/buildcfg"
 	"internal/diff"
 	"internal/testenv"
 	"slices"
@@ -24,6 +25,10 @@ func TestStd(t *testing.T) {
 			list = append(list, pkg)
 		}
 	}
+	// TODO remove this when simd is the default, for now fake its existence
+	if !buildcfg.Experiment.SIMD {
+		list = append(list, "simd")
+	}
 	slices.Sort(list)
 
 	have := strings.Join(stdPkgs, "\n") + "\n"

src/simd/cpu.go

@@ -0,0 +1,20 @@
+// Copyright 2025 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.
+
+//go:build goexperiment.simd
+
+// the build condition == if the experiment is not on, cmd/api TestCheck will see this and complain
+// see also go/doc/comment, where "simd" is inserted to the package list of the experiment is not on.
+
+package simd
+
+import "internal/cpu"
+
+func HasAVX512BW() bool {
+	return cpu.X86.HasAVX512BW
+}
+
+func HasAVX512VL() bool {
+	return cpu.X86.HasAVX512VL
+}