by goprogger@gmx.de:

Before filing a bug, please check whether it has been fixed since
the latest release: run "hg pull -u" and retry what you did to
reproduce the problem.  Thanks.

What steps will reproduce the problem?
package main

Version 1.go:
-------------

import (
    "fmt"
    "runtime"
)

func main() {
    F(15000000)
}

func F(n int) (r string) {
    r2 := ""
    for len(r2 + r) < n {
        t := ""

        for i := 0; i < 5000; i++ {
            t += "10"
        }
        r += t

        if len(r) > 1000000 {
            fmt.Printf("Alloc:  %12d\n", runtime.MemStats.Alloc)
            r2 += r
            r = ""
        }
    }

    r2 += r
    return r2[:n]
}

Version 0.go (crushes ever faster):
-----------------------------------

package main

import (
    "fmt"
    "runtime"
    "crypto/rand"
)

func main() {
    F(15000000)

    b := make([]byte, 1000)
    _, err := rand.Read(b)
    if err != nil {
        return
    }
}

func F(n int) (r string) {
    r2 := ""
    for len(r2 + r) < n {
        t := ""

        for i := 0; i < 5000; i++ {
            t += "10"
        }
        r += t

        if len(r) > 1000000 {
            fmt.Printf("Alloc:    %10d\n", runtime.MemStats.Alloc)
            r2 += r
            r = ""
        }
    }

    r2 += r
    return r2[:n]
}


What is the expected output?
Output of 0.go compiled with 6g

Alloc:       2730712
Alloc:       4285864
Alloc:       6966696
Alloc:       6770088
Alloc:      13104552
Alloc:      13534632
Alloc:      17578920
Alloc:      19774376
Alloc:      18771368
Alloc:      17745320
Alloc:      16735656
Alloc:      16569768
Alloc:      58090368
Alloc:      60248960


What do you see instead?

Output 386 0.go

Alloc:       4590192
Alloc:      18337264
Alloc:      24819696
Alloc:     354659856
runtime: memory allocated by OS not in usable range
runtime: out of memory: cannot allocate 4325376-byte block (535953408 in use)
throw: out of memory

runtime.throw+0x43 /home/ubuntu/go/src/pkg/runtime/runtime.c:102
    runtime.throw(0x80f3005, 0x413)
runtime.mallocgc+0x2cd /home/ubuntu/go/src/pkg/runtime/malloc.c:60
    runtime.mallocgc(0x4127b1, 0x0, 0x1, 0x1, 0x0, ...)
runtime.mal+0x43 /home/ubuntu/go/src/pkg/runtime/malloc.c:289
    runtime.mal(0x4127b1, 0x805bfb1)
runtime.gostringsize+0x49 /home/ubuntu/go/src/pkg/runtime/string.c:40
    runtime.gostringsize(0x80fe4c, 0x4127b0, 0x2710)
concatstring+0x79 /home/ubuntu/go/src/pkg/runtime/string.c:126
    concatstring(0x80fe88, 0x2, 0x80fe78, 0x80fe78)
runtime.concatstring+0x1f /home/ubuntu/go/src/pkg/runtime/string.c:141
    runtime.concatstring(0x2, 0xaf067000, 0x3da540)
main.F+0x6a /home/ubuntu/test/0.go:21
    main.F(0xe4e1c0, 0xb6c33000, 0x38270)
main.main+0x26 /home/ubuntu/test/0.go:10
    main.main()
runtime.mainstart+0xf /home/ubuntu/go/src/pkg/runtime/386/asm.s:93
    runtime.mainstart()
runtime.goexit /home/ubuntu/go/src/pkg/runtime/proc.c:178
    runtime.goexit()
----- goroutine created by -----
_rt0_386+0xc1 /home/ubuntu/go/src/pkg/runtime/386/asm.s:80



--------------------------------------------------------------------------
Output 386 1.go

Alloc:       3840488
Alloc:       4666216
Alloc:       8051560
Alloc:       6943592
Alloc:       8584040
Alloc:      13527912
Alloc:      20775784
Alloc:      91599424
Alloc:     424534984
runtime: memory allocated by OS not in usable range
runtime: out of memory: cannot allocate 9175040-byte block (536805376 in use)
throw: out of memory

runtime.throw+0x43 /home/ubuntu/go/src/pkg/runtime/runtime.c:102
    runtime.throw(0x80e9005, 0x8b1)
runtime.mallocgc+0x2cd /home/ubuntu/go/src/pkg/runtime/malloc.c:60
    runtime.mallocgc(0x8b01f1, 0x0, 0x1, 0x1, 0x0, ...)
runtime.mal+0x43 /home/ubuntu/go/src/pkg/runtime/malloc.c:289
    runtime.mal(0x8b01f1, 0x805bf4a)
runtime.gostringsize+0x49 /home/ubuntu/go/src/pkg/runtime/string.c:40
    runtime.gostringsize(0x307e8c, 0x8b01f0, 0x2710)
concatstring+0x79 /home/ubuntu/go/src/pkg/runtime/string.c:126
    concatstring(0x307ec8, 0x2, 0x307eb8, 0x307eb8)
runtime.concatstring+0x1f /home/ubuntu/go/src/pkg/runtime/string.c:141
    runtime.concatstring(0x2, 0xb5d6d000, 0x8ab3d0)
main.F+0x6a /home/ubuntu/test/1.go:14
    main.F(0xe4e1c0, 0xb451f000, 0x4e20)
main.main+0x26 /home/ubuntu/test/1.go:9
    main.main()
runtime.mainstart+0xf /home/ubuntu/go/src/pkg/runtime/386/asm.s:93
    runtime.mainstart()
runtime.goexit /home/ubuntu/go/src/pkg/runtime/proc.c:178
    runtime.goexit()
----- goroutine created by -----
_rt0_386+0xc1 /home/ubuntu/go/src/pkg/runtime/386/asm.s:80

Which compiler are you using (5g, 6g, 8g, gccgo)?
8g

Which operating system are you using?
ubuntu 10.04, 10.10, 11.04

Which revision are you using?  (hg identify)
e1e194eb5c8e (release-branch.r57)

Please provide any additional information below.