[Vm-dev] VM Maker: VMMaker.oscog-eem.2603.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.2603.mcz

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

Name: VMMaker.oscog-eem.2603
Author: eem
Time: 8 December 2019, 11:47:29.689495 am
UUID: aed4d5c3-3e5c-4e35-8897-c6f199406ccb
Ancestors: VMMaker.oscog-eem.2602

Make A64 immediate logical bitmasks correct.

=============== Diff against VMMaker.oscog-eem.2602 ===============

Item was added:
+ ----- Method: CogARMv8Compiler>>decode64Imms:immr: (in category 'generate machine code - support') -----
+ decode64Imms: imms immr: immr
+ 	"See aarch64/instrs/integer/bitmasks/DecodeBitMasks J1-7389.
+ 	 This is a 64-bit version computing the imm mask (wmask) only."
+ 	| mask |
+ 	self assert: ((imms between: 0 and: 63) and: (immr between: 0 and: 63)).
+ 	"For logical immediates an all-ones value of S is reserved since it would generate a useless all-ones result (many times)"
+ 	imms = 63 ifTrue:
+ 		[^self cCode: [0] inSmalltalk: [#undefined]].
+ 
+ 	mask := 1 << (imms + 1) - 1.
+ 	^immr = 0
+ 		ifTrue: [mask]
+ 		ifFalse: [(mask << (64 - immr) bitAnd: 1 << 64 - 1) + (mask >> immr)]!

Item was removed:
- ----- Method: CogARMv8Compiler>>decodeBitMasksN:imms:immr: (in category 'generate machine code - support') -----
- decodeBitMasksN: immN imms: imms immr: immr
- 	"See aarch64/instrs/integer/bitmasks/DecodeBitMasks J1-7389"
- 	| tmask wmask levels |
- 	"eem 12/3/2019 18:17
- 	 In
- 
- 		len = HighestSetBit(immN:NOT(imms));
- 
- 	 I have no clue what is meant by
- 
- 		immN:NOT(imms)
- 
- 	 Reading Arm Pseudocode Definition K13.4 Operators leaves me none the wiser."
- 	self shouldBeImplemented!

Item was changed:
  ----- Method: CogARMv8Compiler>>isImmNImmSImmREncodableBitmask:ifTrue:ifFalse: (in category 'generate machine code - support') -----
  isImmNImmSImmREncodableBitmask: constant ifTrue: trinaryBlock "[:n :imms :immr|...]" ifFalse: nullaryBlock
  	"See DecodeBitMasks J1-7389.
  	 See https://dinfuehr.github.io/blog/encoding-of-immediate-values-on-aarch64/
  	 This method is adapted from The LLVM Compiler Infrastructure, AArch64AddressingModes.h processLogicalImmediate"
  
  	| imm size mask countLeadingOnes countTrailingOnes immr n nImms rotateCount |
  	(constant between: -1 and: 0) ifTrue:
  		[^nullaryBlock value].
  	imm := constant.
   
  	"First, determine the element size."
  	size := 32.
  	[mask := 1 << size - 1.
  	 (imm bitAnd: mask) ~= (imm >> size)
  			ifTrue: [size := size * 2. false]
  			ifFalse: [size > 2]]
  		whileTrue: [size := size / 2].
  
  	"Second, determine the rotation to make the element be: 0^m 1^n."
  	mask := 1 << 64 - 1 >> (64 - size).
  	imm := imm bitAnd: mask.
  
  	(self isShiftedMask: imm)
  		ifTrue:
  			[rotateCount := self countTrailingZeros: imm.
  			 countTrailingOnes := self countTrailingOnes: imm >> rotateCount]
  		ifFalse:
  			[imm := imm bitOr: mask bitInvert64.
  			 (self isShiftedMask: imm) ifFalse:
  				[^nullaryBlock value].
  			 countLeadingOnes := self countLeadingOnes: imm.
  			 rotateCount := 64 - countLeadingOnes.
  			 countTrailingOnes := countLeadingOnes + (self countTrailingOnes: imm) - (64 - size)].
  
  	"Encode in Immr the number of RORs it would take to get *from* 0^m 1^n
  	 to our target value, where I is the number of RORs to go the opposite direction."
   
  	self assert: size > rotateCount. "rotateCount should be smaller than element size"
  	immr := size - rotateCount bitAnd: size - 1.
  
  	"If size has a 1 in the n'th bit, create a value that has zeroes in bits [0, n] and ones above that."
  	nImms := (size - 1) bitInvert64 << 1.
  
  	"Or the CTO value into the low bits, which must be below the Nth bit mentioned above."
  	nImms := nImms bitOr:  countTrailingOnes - 1.
  
  	"Extract the seventh bit and toggle it to create the N field."
  	n := ((nImms >> 6) bitAnd: 1) bitXor: 1.
  
  	nImms := nImms bitAnd: 16r3F.
  
+ 	self assert: (self decode64Imms: nImms immr: immr) = constant.
- 	false ifTrue: [self assert: (self decodeBitMasksN: n imms: nImms immr: immr) = constant].
  
  	^trinaryBlock
  		value: n
  		value: nImms
  		value: immr
  !