A minor issue with register allocator

[sig]

I'm already found a bug. It was in my code, which introduced problems
with registers.
Sorry for disturbing :)

On 28/06/07, bryce at kampjes.demon.co.uk <bryce at kampjes.demon.co.uk> wrote:
> sig writes:
>  > I'm currently testing my asm-parser. And found it generates unneeded
>  > instruction (mov eax,eax):
>  > code of asm method:
>  >
>  > message4: arg1 with: arg2
>  >      | b c |
>  >      self pragma: #cdecl.
>  >      c := arg1 + arg2.
>  >      b := arg1 / arg2.
>  >      ^ c + b
>  >
>  > produced intermediate by parser:
>  > #(#(#block 1
>  > #(#mov #(#add #(#argument #arg1) #(#argument #arg2)) #c)
>  > #(#mov #(#div #(#argument #arg1) #(#argument #arg2) 'temp7D6') #b)
>  > #(#return #(#add #c #b))))
>  >
>  > then with transformed arguments and cdecl prologue/epilogue:
>  > #(#(#block 1 #(#push #ebp) #(#mov #esp #ebp)) #(#block 3
>  >  #(#mov #(#add #(#mem #(#add #ebp -4)) #(#mem #(#add #ebp -8))) 't1')
>  > #(#mov #(#div #(#mem #(#add #ebp -4)) #(#mem #(#add #ebp -8)) 't3') 't2')
>  > #(#mov #(#add 't1' 't2') #eax) #(#jmp #block2)) #(#block 2 #(#mov #ebp
>  > #esp) #(#pop #ebp) #(#ret)))
>  >
>  > and then i using
>  > LowLevelOptimiser ->InstructionSelector -> ColouringRegisterAllocator
>  > -> JumpRemover :
>  >
>  > #(#(#block 1 #(#push #ebp) #(#mov #esp #ebp)) #(#block 3 #(#mov #(-8
>  > #ebp) #ebx) #(#add #(-4 #ebp) #ebx) #(#mov #(-4 #ebp) #eax) #(#mov
>  > #(-8 #ebp) #ecx) #(#cdq) #(#div #ecx)
>  >
>  > #(#mov #eax #eax)
>  >
>  > #(#add #ebx #eax)) #(#block 2 #(#mov #ebp #esp) #(#pop #ebp) #(#ret)))
>  >
>  > I suppose fix could be simple by testing in MedMov>>#visitWith: that
>  > if reg1 = reg2 then return nil , which will be interpreted as no-op by
>  > block.
>
> I'm not sure why Exupery is doing that. The register uses a decent
> move coalescer which will first try to create moves like (mov eax eax)
> then remove them. The register allocator goes to some lengths to do
> this.
>
> It's possible that you've found a case where the no-op move removal
> code isn't getting used, though I'm not sure where it is. It will be
> interesting to here if the problem is still there after you change how
> you're creating intermediate to make sure that there's only one #eax
> register object. 1)
>
> Exupery relies on object identity inside it's intermediate, this is
> a design decision that's probabably in many places by now.
>
> Bryce
>
> 1) Sig and I've spoken on irc about this.
> _______________________________________________
> Exupery mailing list
> Exupery at lists.squeakfoundation.org
> http://lists.squeakfoundation.org/cgi-bin/mailman/listinfo/exupery
>