benchmarks: Add a basic set of benchmarks

Add google benchmark to the DEPs.

Implement a basic set of benchmarks for each of the writers and the WGSL parser.

Add build rules for CMake. GN build rules TODO.

Add a simple go tool (ported from Marl) to diff two benchmarks. Less
noisy than the one provided by google benchmark.

Bug: tint:1378
Change-Id: I73cf92c5d9fd2d3bfac8f264864fd774afbd5d01
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/76840
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: Ryan Harrison <rharrison@chromium.org>
Commit-Queue: Ben Clayton <bclayton@chromium.org>

tools/src/bench/bench.go

@@ -0,0 +1,150 @@
+// Copyright 2022 The Tint Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package bench provides types and methods for parsing Google benchmark results.
+package bench
+
+import (
+	"encoding/json"
+	"errors"
+	"fmt"
+	"regexp"
+	"strconv"
+	"strings"
+	"time"
+)
+
+// Test holds the results of a single benchmark test.
+type Test struct {
+	Name       string
+	NumTasks   uint
+	NumThreads uint
+	Duration   time.Duration
+	Iterations uint
+}
+
+var testVarRE = regexp.MustCompile(`([\w])+:([0-9]+)`)
+
+func (t *Test) parseName() {
+	for _, match := range testVarRE.FindAllStringSubmatch(t.Name, -1) {
+		if len(match) != 3 {
+			continue
+		}
+		n, err := strconv.Atoi(match[2])
+		if err != nil {
+			continue
+		}
+		switch match[1] {
+		case "threads":
+			t.NumThreads = uint(n)
+		case "tasks":
+			t.NumTasks = uint(n)
+		}
+	}
+}
+
+// Benchmark holds a set of benchmark test results.
+type Benchmark struct {
+	Tests []Test
+}
+
+// Parse parses the benchmark results from the string s.
+// Parse will handle the json and 'console' formats.
+func Parse(s string) (Benchmark, error) {
+	type Parser = func(s string) (Benchmark, error)
+	for _, parser := range []Parser{parseConsole, parseJSON} {
+		b, err := parser(s)
+		switch err {
+		case nil:
+			return b, nil
+		case errWrongFormat:
+		default:
+			return Benchmark{}, err
+		}
+	}
+
+	return Benchmark{}, errors.New("Unrecognised file format")
+}
+
+var errWrongFormat = errors.New("Wrong format")
+var consoleLineRE = regexp.MustCompile(`([\w/:]+)\s+([0-9]+(?:.[0-9]+)?) ns\s+[0-9]+(?:.[0-9]+) ns\s+([0-9]+)`)
+
+func parseConsole(s string) (Benchmark, error) {
+	blocks := strings.Split(s, "------------------------------------------------------------------------------------------")
+	if len(blocks) != 3 {
+		return Benchmark{}, errWrongFormat
+	}
+
+	lines := strings.Split(blocks[2], "\n")
+	b := Benchmark{
+		Tests: make([]Test, 0, len(lines)),
+	}
+	for _, line := range lines {
+		if len(line) == 0 {
+			continue
+		}
+		matches := consoleLineRE.FindStringSubmatch(line)
+		if len(matches) != 4 {
+			return Benchmark{}, fmt.Errorf("Unable to parse the line:\n" + line)
+		}
+		ns, err := strconv.ParseFloat(matches[2], 64)
+		if err != nil {
+			return Benchmark{}, fmt.Errorf("Unable to parse the duration: " + matches[2])
+		}
+		iterations, err := strconv.Atoi(matches[3])
+		if err != nil {
+			return Benchmark{}, fmt.Errorf("Unable to parse the number of iterations: " + matches[3])
+		}
+
+		t := Test{
+			Name:       matches[1],
+			Duration:   time.Nanosecond * time.Duration(ns),
+			Iterations: uint(iterations),
+		}
+		t.parseName()
+		b.Tests = append(b.Tests, t)
+	}
+	return b, nil
+}
+
+func parseJSON(s string) (Benchmark, error) {
+	type T struct {
+		Name       string  `json:"name"`
+		Iterations uint    `json:"iterations"`
+		Time       float64 `json:"real_time"`
+	}
+	type B struct {
+		Tests []T `json:"benchmarks"`
+	}
+	b := B{}
+	d := json.NewDecoder(strings.NewReader(s))
+	if err := d.Decode(&b); err != nil {
+		return Benchmark{}, err
+	}
+
+	out := Benchmark{
+		Tests: make([]Test, len(b.Tests)),
+	}
+	for i, test := range b.Tests {
+		t := Test{
+			Name:       test.Name,
+			Duration:   time.Nanosecond * time.Duration(int64(test.Time)),
+			Iterations: test.Iterations,
+		}
+		t.parseName()
+		out.Tests[i] = t
+	}
+
+	return out, nil
+}