runtime: computed hash value for struct map key ignores some fields #3695

This is possibly a duplicate of 3573, but is logged since the problem does not appear to
be completely fixed at tip, so it was suggested that I relog.

$ go version
go version weekly.2012-03-27 +d8e47164f8dd

What steps will reproduce the problem?
If possible, include a link to a program on play.golang.org.
1. Run one of the variations of the program at:
http://play.golang.org/p/wG8AK7AAQl

Variations include changing const id = ... to var id = ... and also changing the values
assigned to id. The struct sp can also be defined as a struct { string int string int }
to the same effect as presented in the linked code.

What is the expected output?
The numbers 0-499 on separate line.


What do you see instead?
The numbers 0-81 on separate lines followed by any of (variable results for any given
program):
1. 'throw: hashmap assert'
when id is const or var "", var or const "a", var ~>
"naaa" (4-words checked only)

2. 'invalid memory address or nil pointer dereference'
when id is var ""

3. 'unexpected fault address'
when id is const or var "a" or ~< "naaa" (4-words checked)

4. no termination with 100% CPU usage.
when id is const or var ~> "naaa" (4-words checked only)

NB 4-words not exhaustively checked.

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

Which operating system are you using?
Linux

Which version are you using?  (run 'go version')
go version weekly.2012-03-27 +d8e47164f8dd

Please provide any additional information below.
Using sf with only the int field or the string field results in normal behaviour.