rtl dependency

rtl dependency

[Danish Samad]

hello,
 
 I have observed that different cross compilers
produce different RTL for the same peice of code.
Does this mean that unoptimized RTL generated is
dependent on target description macros if yes then
which macros? or is it only dependent on machine
descriptions? Further what would I have to do to
produce load store RTL instructions for a
initialization such as i=4;

thanking in advance,
danish 

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Re: rtl dependency

[Alan Lehotsky]

At 5:59 AM -0800 2/26/02, Danish Samad wrote:

>hello,
> 
> I have observed that different cross compilers
>produce different RTL for the same peice of code.

	Yes.

>Does this mean that unoptimized RTL generated is
>dependent on target description macros if yes then
>which macros?

	A great many of them!  Pretty much all the things described in the sections of the porting guide
	that discuss Register Characteristics, Passing Arguments/ Stack Layout, Storage Layout, and Addressing
	Modes.

> or is it only dependent on machine
>descriptions?

	It's driven by the named patterns - like "movsi", "addsi3", etc. that the tree conversion
	code in expr.c and optabs.c knows about - but the target macros influence heavily what happens.

>Further what would I have to do to
>produce load store RTL instructions for a
>initialization such as i=4;

	Look at an existing load/store machine - there are a bunch of 'em.

	Typically what you do is write a "movsi" define_expand pattern that checks to see if at least
	one of the operands is a REG and forces the OTHER operand to a register.  E.g., if you tried to
	do a memory-to-memory move, you'd force the source to a register and then move that
	register to memory.
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