Add -memprofile option to l-tm

For profiling memory allocations used for producing reproducible
instructions for analysing allocations.

Usage:

This command collects a profile:

```
l-tm -memprofile=mem.pprof <input llvm>
```

This one loads pprof in a mode showing all allocations that occurred by
count (rather than by size, which is alloc_space).

```
go tool pprof -sample_index=alloc_objects mem.pprof
```

Useful commands thereafter: `top10` or `web`.

cmd/l-tm/main.go

@@ -5,24 +5,33 @@ import (
 	"fmt"
 	"log"
 	"os"
+	"runtime"
 	"runtime/pprof"
 	"time"
 
 	"github.com/llir/llvm/asm"
 )
 
 func main() {
-	var cpuprofile string
-	flag.StringVar(&cpuprofile, "cpuprofile", "", "write cpu profile to file")
+	var (
+		cpuprofile = flag.String("cpuprofile", "", "write cpu profile to file")
+		memprofile = flag.String("memprofile", "", "write mem profile to file")
+	)
 	flag.Parse()
-	if cpuprofile != "" {
-		f, err := os.Create(cpuprofile)
+
+	if *cpuprofile != "" {
+		fd, err := os.Create(*cpuprofile)
 		if err != nil {
 			log.Fatalf("%+v", err)
 		}
-		pprof.StartCPUProfile(f)
+		pprof.StartCPUProfile(fd)
 		defer pprof.StopCPUProfile()
 	}
+
+	if *memprofile != "" {
+		runtime.MemProfileRate = 1
+	}
+
 	for _, llPath := range flag.Args() {
 		fmt.Printf("=== [ %v ] =======================\n", llPath)
 		fmt.Println()
@@ -35,4 +44,17 @@ func main() {
 		_ = m
 		//pretty.Println(m)
 	}
+
+	if *memprofile != "" {
+		fd, err := os.Create(*memprofile)
+		if err != nil {
+			log.Fatalf("%+v", err)
+		}
+		runtime.GC()
+		err = pprof.WriteHeapProfile(fd)
+		if err != nil {
+			log.Fatalf("WriteHeapProfile: %v", err)
+		}
+
+	}
 }