[Vm-dev] VM Maker: VMMaker.oscog-eem.2791.mcz

[commits at source.squeak.org]

Eliot Miranda uploaded a new version of VMMaker to project VM Maker:
http://source.squeak.org/VMMaker/VMMaker.oscog-eem.2791.mcz

==================== Summary ====================

Name: VMMaker.oscog-eem.2791
Author: eem
Time: 19 August 2020, 6:21:04.014485 pm
UUID: 04cdce33-b4a9-4acb-982e-ed9393a1783b
Ancestors: VMMaker.oscog-eem.2790

Looking at class indentityHash distributions in my current VMMaker image it is clear that setting the classTableIndex to point at the start of the last used page is not a good strategy, and leads to far too sparse a class table.  So change the policy and set the classTableIndex to the first unused slot (unless bootstrapping).

=============== Diff against VMMaker.oscog-eem.2790 ===============

Item was changed:
  ----- Method: SpurMemoryManager>>setHiddenRootsObj: (in category 'class table') -----
  setHiddenRootsObj: anOop
  	hiddenRootsObj := anOop.
  	self cCode: [self assert: self validClassTableRootPages]
  		inSmalltalk: [numClassTablePages ifNotNil:
  						[self assert: self validClassTableRootPages]].
  	classTableFirstPage := self fetchPointer: 0 ofObject: hiddenRootsObj.
  	self assert: (self numSlotsOf: classTableFirstPage) - 1 = self classTableMinorIndexMask.
  	"Hack fix.  A bug in markAndTraceClassOf: caused the class of the first class table page
  	 to be changed from its pun.  This can be restored manually, but we do it here too."
  	self flag: 'remove at some stage'.
  	(self classIndexOf: classTableFirstPage) ~= self arrayClassIndexPun ifTrue:
  		[self setClassIndexOf: classTableFirstPage to: self arrayClassIndexPun].
- 	"Set classTableIndex to the start of the last used page (excepting first page).
- 	 Set numClassTablePages to the number of used pages."
  	numClassTablePages := self classTableRootSlots.
+ 	self bootstrapping ifTrue:
+ 		["Set classTableIndex to the start of the last used page (excepting first page).
+ 		  Set numClassTablePages to the number of used pages."
+ 		2 to: numClassTablePages - 1 do:
+ 			[:i|
+ 			(self fetchPointer: i ofObject: hiddenRootsObj) = nilObj ifTrue:
+ 				[numClassTablePages := i.
+ 				 classTableIndex := (i - 1 max: 1) << self classTableMajorIndexShift.
+ 				 ^self]].
+ 		"no unused pages; set it to the start of the second page."
+ 		classTableIndex := 1 << self classTableMajorIndexShift.
+ 		^self].
+ 	"If loading an image, set the classTableIndex to the first unused slot in the class table after the first page.
+ 	 Set numClassTablePages to the number of used pages.
+ 	 Set classTableIndex to point at the first unused entry. First set it to the max as a sentinel."
+ 	classTableIndex := numClassTablePages << self classTableMajorIndexShift.
+ 	1 to: numClassTablePages - 1 do:
+ 		[:i| | page j |
+ 		(page := self fetchPointer: i ofObject: hiddenRootsObj) = nilObj
+ 			ifFalse:
+ 				[classTableIndex >> self classTableMajorIndexShift > i ifTrue:
+ 					[j := 0.
+ 					 [j < self classTablePageSize] whileTrue:
+ 						[(self fetchPointer: j ofObject: page) = nilObj ifTrue:
+ 							[classTableIndex := i << self classTableMajorIndexShift + j.
+ 							 j := self classTablePageSize].
+ 						 j := j + 1]]]
+ 			ifTrue:
+ 				[classTableIndex >> self classTableMajorIndexShift > i ifTrue:
+ 					[classTableIndex := (i - 1 max: 1) << self classTableMajorIndexShift].
+ 				 numClassTablePages := i.
+ 				 self assert: (self classOrNilAtIndex: classTableIndex) = nilObj.
+ 				 ^self]].
+ 	"no unused slots; set it to the start of the second page."
+ 	classTableIndex >> self classTableMajorIndexShift >= numClassTablePages ifTrue:
+ 		[classTableIndex := 1 << self classTableMajorIndexShift].
+ 	 self assert: (self classOrNilAtIndex: classTableIndex) = nilObj!
- 	2 to: numClassTablePages - 1 do:
- 		[:i|
- 		(self fetchPointer: i ofObject: hiddenRootsObj) = nilObj ifTrue:
- 			[numClassTablePages := i.
- 			 classTableIndex := (numClassTablePages - 1 max: 1) << self classTableMajorIndexShift.
- 			 ^self]].
- 	"no unused pages; set it to the start of the second page."
- 	classTableIndex := 1 << self classTableMajorIndexShift!