What steps will reproduce the problem?
If possible, include a link to a program on play.golang.org.
1. Run http://play.golang.org/p/JF29YmJKun

This also occurs when building archive/zip and archive/tar, among several others in the
standard library.

What is the expected output?

No output, zero return code

What do you see instead?

panic: no concrete method: func (*math/big.Int).SetInt64(x int64) *math/big.Int

goroutine 1 [running]:
runtime.panic(0x5dd740, 0xc21007b660)
    /home/andrew/prog/go/root/src/pkg/runtime/panic.c:266 +0xb6
code.google.com/p/go.tools/ssa.(*Program).declaredFunc(0xc2100514e0, 0xc21008abc0,
0xc21005f380)
    /media/msata/code/src/code.google.com/p/go.tools/ssa/promote.go:166 +0xff
code.google.com/p/go.tools/ssa.(*builder).setCallFunc(0x7f5aa726fb3f, 0xc2100ff000,
0xc210069900, 0xc21011b1c0)
    /media/msata/code/src/code.google.com/p/go.tools/ssa/builder.go:817 +0x2e6
code.google.com/p/go.tools/ssa.(*builder).setCall(0x7f5aa726fb3f, 0xc2100ff000,
0xc210069900, 0xc21011b1c0)
    /media/msata/code/src/code.google.com/p/go.tools/ssa/builder.go:910 +0x59
code.google.com/p/go.tools/ssa.(*builder).expr0(0x7f5aa726fb3f, 0xc2100ff000,
0x7f5aa740f788, 0xc210069900, 0x0, ...)
    /media/msata/code/src/code.google.com/p/go.tools/ssa/builder.go:541 +0x18c4
code.google.com/p/go.tools/ssa.(*builder).expr(0x7f5aa726fb3f, 0xc2100ff000,
0x7f5aa740f788, 0xc210069900, 0x200409400, ...)
    /media/msata/code/src/code.google.com/p/go.tools/ssa/builder.go:474 +0x1a8
code.google.com/p/go.tools/ssa.(*builder).exprInPlace(0x7f5aa726fb3f, 0xc2100ff000,
0x7f5aa7414878, 0xc2101177e0, 0x7f5aa740f788, ...)
    /media/msata/code/src/code.google.com/p/go.tools/ssa/builder.go:462 +0x246
code.google.com/p/go.tools/ssa.(*Package).Build(0xc21005ae70)
    /media/msata/code/src/code.google.com/p/go.tools/ssa/builder.go:2236 +0xa85
main.buildSSA(0xc21001daf0, 0x69d930, 0xc, 0x7f5aa740f0e0, 0x960d80)
    /tmp/bug/bug.go:52 +0x3aa
main.main()
    /tmp/bug/bug.go:63 +0x79


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

6g

Which operating system are you using?

GNU/Linux (Ubuntu 13.10)

Which version are you using?  (run 'go version')

go version go1.2 linux/amd64