prog: fix a data race

The race initially showed up on the new benchmark (see race report below).
The race indicated a wrong call passed to replaceArg,
as the result we sanitized the wrong call and left the new call un-sanitized.

Fix this.
Add test that exposes this.
Run benchmarks in race mode during presubmit
(benchmarks have higher chances of uncovering races than tests).

WARNING: DATA RACE
Write at 0x00c42000d3f0 by goroutine 18:
  github.com/google/syzkaller/sys/linux.(*arch).sanitizeCall()
      sys/linux/init.go:155 +0x256
  github.com/google/syzkaller/sys/linux.(*arch).(github.com/google/syzkaller/sys/linux.sanitizeCall)-fm()
      sys/linux/init.go:42 +0x4b
  github.com/google/syzkaller/prog.(*Prog).replaceArg()
      prog/prog.go:357 +0x239
  github.com/google/syzkaller/prog.generateHints.func2()
      prog/hints.go:105 +0x124
  github.com/google/syzkaller/prog.checkConstArg()
      prog/hints.go:128 +0xf3
  github.com/google/syzkaller/prog.generateHints()
      prog/hints.go:120 +0x495
  github.com/google/syzkaller/prog.(*Prog).MutateWithHints.func1()
      prog/hints.go:72 +0x67
  github.com/google/syzkaller/prog.foreachSubargImpl.func1()
      prog/analysis.go:86 +0x9f
  github.com/google/syzkaller/prog.foreachSubargImpl()
      prog/analysis.go:104 +0xc8
  github.com/google/syzkaller/prog.foreachArgArray()
      prog/analysis.go:113 +0x89
  github.com/google/syzkaller/prog.foreachArg()
      prog/analysis.go:121 +0x50
  github.com/google/syzkaller/prog.(*Prog).MutateWithHints()
      prog/hints.go:71 +0x18e
  github.com/google/syzkaller/prog.BenchmarkHints.func1()
      prog/hints_test.go:477 +0x77
  testing.(*B).RunParallel.func1()
      testing/benchmark.go:626 +0x156

Previous read at 0x00c42000d3f0 by goroutine 17:
  github.com/google/syzkaller/prog.clone()
      prog/clone.go:38 +0xbaa
  github.com/google/syzkaller/prog.(*Prog).cloneImpl()
      prog/clone.go:21 +0x17f
  github.com/google/syzkaller/prog.generateHints()
      prog/hints.go:95 +0xd0
  github.com/google/syzkaller/prog.(*Prog).MutateWithHints.func1()
      prog/hints.go:72 +0x67
  github.com/google/syzkaller/prog.foreachSubargImpl.func1()
      prog/analysis.go:86 +0x9f
  github.com/google/syzkaller/prog.foreachSubargImpl()
      prog/analysis.go:104 +0xc8
  github.com/google/syzkaller/prog.foreachArgArray()
      prog/analysis.go:113 +0x89
  github.com/google/syzkaller/prog.foreachArg()
      prog/analysis.go:121 +0x50
  github.com/google/syzkaller/prog.(*Prog).MutateWithHints()
      prog/hints.go:71 +0x18e
  github.com/google/syzkaller/prog.BenchmarkHints.func1()
      prog/hints_test.go:477 +0x77
  testing.(*B).RunParallel.func1()
      testing/benchmark.go:626 +0x156

1 files changed, 29 insertions, 0 deletions

diff --git a/prog/hints_test.go b/prog/hints_test.go
index b5e35c9c9..b2999ad14 100644
--- a/prog/hints_test.go
+++ b/prog/hints_test.go
@@ -6,6 +6,7 @@ package prog
 import (
 	"encoding/hex"
 	"fmt"
+	"math/rand"
 	"reflect"
 	"sort"
 	"testing"
@@ -450,3 +451,31 @@ func TestHintsData(t *testing.T) {
 		}
 	}
 }
+
+func BenchmarkHints(b *testing.B) {
+	target, err := GetTarget("linux", "amd64")
+	if err != nil {
+		b.Fatal(err)
+	}
+	rs := rand.NewSource(0)
+	r := newRand(target, rs)
+	p := target.Generate(rs, 30, nil)
+	comps := make([]CompMap, len(p.Calls))
+	for i, c := range p.Calls {
+		vals := extractValues(c)
+		for j := 0; j < 5; j++ {
+			vals[r.randInt()] = true
+		}
+		comps[i] = make(CompMap)
+		for v := range vals {
+			comps[i].AddComp(v, r.randInt())
+		}
+	}
+	b.RunParallel(func(pb *testing.PB) {
+		for pb.Next() {
+			for i := range p.Calls {
+				p.MutateWithHints(i, comps[i], func(p1 *Prog) {})
+			}
+		}
+	})
+}