[M3commit] CVS Update: cm3

[Jay Krell]

CVSROOT:	/usr/cvs
Changes by:	jkrell at birch.	10/03/13 19:11:14

Modified files:
	cm3/m3-sys/m3back/src/: Codex86.m3 M3x86.m3 Stackx86.m3 

Log message:
	improve all integer compares, some/all set compares
	not yet: float compares
	
	old pattern:
	cmp
	setcc byte in memory
	xor reg,reg (any register, I believe)
	mov reg, memory
	
	new patterns, depending on comparison/types:
	xor reg, reg (register restricted to RegistersForByteOperations = {EAX, EBX, ECX, EDX}
	cmp
	setcc reg
	
	or
	cmp possibly with operands reversed
	sbb reg, reg
	neg reg
	
	or
	cmp possibly with operands reversed
	sbb reg, reg
	inc reg
	
	There is a little extra pressure on eax,ebx,ecx,edx, but
	we save an instruction and we avoid use of an in-memory temporary.
	The instruction could have been saved by using movzx as the manuals
	recommend anyway, instead of xor+mov.
	
	The sequences are used are based on optimized C.
	
	Basic problem here is setcc which only sets a byte
	but we generally want 32bit values.
	
	Possibly more to do here.
	
	The main difficulty developing this change was
	that I didn't initially restrict to RegistersForByteOperations.
	Small test cases worked ok but cases with more register pressure did not.
	see test p232 for a test that currently exercises some of this.