It's a bit dangerous to change the hash without rehashing the collections 
which contain CompiledMethods as keys. For example DebuggerMethodMap's 
MapCache uses CompiledMethods as keys.


Levente

On Sun, 27 May 2012, commits at source.squeak.org wrote:

> Eliot Miranda uploaded a new version of Kernel to project The Trunk:
> http://source.squeak.org/trunk/Kernel-eem.692.mcz
>
> ==================== Summary ====================
>
> Name: Kernel-eem.692
> Author: eem
> Time: 27 May 2012, 3:08:41.389 pm
> UUID: 72f75218-3cfc-4575-b159-8de0e44aa479
> Ancestors: Kernel-nice.691
>
> Implement CompiledMethod>>#hash, both to accord with
> CompiledMethod>>#= and to override ByteArray>>#hash
> which looks at all bytes of the receiver and hence may
> produce a variable hash if the GC moves literals in a method.
>
> =============== Diff against Kernel-nice.691 ===============
>
> Item was added:
> + ----- Method: CompiledMethod>>hash (in category 'comparing') -----
> + hash
> + 	"CompiledMethod>>#= compares code, i.e. same literals and same bytecode.
> + 	 So we look at the header, methodClass and some bytes between initialPC and endPC,
> + 	 but /not/ the selector because the equal method does not compare selectors.
> + 	 Note that we must override ByteArray>hash which looks at all bytes of the receiver.
> + 	 Using bytes from the pointer part of a COmpiledmethod can lead to a variable hash
> + 	 if and when when the GC moves literals in the receiver."
> + 	| initialPC endPC hash |
> + 	initialPC := self initialPC.
> + 	endPC := self endPC.
> + 	hash := self species hash + self header + initialPC + endPC + self methodClass hash bitAnd: 16rFFFFFFF.
> + 	"sample approximately 20 bytes"
> + 	initialPC to: endPC by: (endPC - initialPC // 20 max: 1) do:
> + 		[:i| hash := hash + (self at: i)].
> + 	^hash
> +
> + 	"(CompiledMethod>>#hash) hash"!
>
>
>