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@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"!