[M3devel] cg.compare_exchange should take more parameters in function call, fewer on stack?

[Jay K]

Hm. I think there's a bigger problem here.

I think, not sure, but i think compare_exhcange needs to take a "Var", not an address on the stack.

See how it is storing the address to the stack and comparing that. Wrong.

 

 

 - Jay

 


From: jay.krell at cornell.edu
To: hosking at cs.purdue.edu; m3devel at elegosoft.com
Date: Fri, 12 Feb 2010 09:17:14 +0000
Subject: [M3devel] cg.compare_exchange should take more parameters in function call, fewer on stack?



Tony, currently I have atomic.compare_and_exchange generating e.g.:
 
 
 load_address      gv.2[_MM_Main] 56
 0000018E: 8D3538000000        LEA ESI gv.2[_MM_Main]+56
 load_address      gv.2[_MM_Main] 152
 00000194: 8D3D98000000        LEA EDI gv.2[_MM_Main]+152
 load              gv.2[_MM_Main] 156 Int.32 Int.32
 compare_exchange   Int.32 Int.32 Int.32
 0000019A: 8BC7                MOV EAX EDI
 0000019C: 8B1D9C000000        MOV EBX gv.2[_MM_Main]+156
 declare_temp      4 4 Addr F tv.35[T$35] -4
 000001A2: 8975FC              MOV tv.35[T$35] ESI
 000001A5: F00FB15DFC          LOCK CMPXCHG  tv.35[T$35]:Addr EBX
 

This might not be correct, but it is close.
 

Now, the thing is, the eax register is special to lock cmpxchg.
  It always holds the comparison value.

The point is, if cg.compare_exchange took its parameters as
parameters instead of on the stack, it could chose the
right register right away, instead of as above where it
choses the wrong one and then must mov it.
 
Easy to change it like that?
 

I realize this is an m3back deficiency.
It does the register allocation too early.

 - Jay


 		 	   		  
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