Re: porting gcc for a VLIW architecture

[Jim Wilson <wilson at specifixinc dot com>]

zysheu wrote:
> It is controll by the gcc at the latest pass .  Do I need to define pattern
> to capture all the possible RTL code ?

No.  You only need enough RTL codes such that the rest can be
synthesized from the operations you have defined.

> Do these patterns include standard name pattern and empty name pattern ?

Yes.

> Are expand patterns and split patterns  needed to define asm output ?

No.

Gcc converts trees/gimple to RTL in the middle end.  This is done by
calling patterns in the md file.  Only named define_insn and
define_expand patterns can be called at this time, so this is the only
RTL that can be generated by the middle-end.  After RTL is generated,
all insns must match a define_insn in the md file.

The optimizer uses define_insns to optimize the RTL.  If we create new
RTL during optimization, we do a pattern match to make sure that the new
insn matches a define_insn in the md file.  So you can have additional
unnamed/named patterns which are used for optimization.

Every define_insn has an assembly language template.  When emitting
assembly during the final pass, for each insn, we find the define_insn
it matches and emit the assembly template.

define_split is also used by optimization, except it takes one or more
RTL insns as input and emits one or more RTL insns as output.

You can do a port without using any define_split or define_expand
patterns.  This just allow better optimization and better initial RTL
generation.
-- 
Jim Wilson, GNU Tools Support, http://www.SpecifixInc.com