[tree-ssa] Merge results as of 2003-05-06

[Andrew MacLeod]

On Thu, 2003-05-08 at 11:12, law@redhat.com wrote:
> In message <1052398571.13871.1835.camel@p4>, Andrew MacLeod writes:
>  >On Thu, 2003-05-08 at 03:10, law@redhat.com wrote:
>  >> In message <wvly91i53p6.fsf@prospero.boston.redhat.com>, Jason Merrill writ
>  >es:
>  >
>  >>  >A simple solution may just be to disable all the temp_slots management co
>  >de
>  >>  >when we're using the tree optimizers.  A better solution would be to fix
>  >>  >the temp_slots data structure so that we don't keep slogging through the
>  >>  >whole list when we're only interested in slots from a particular level.
>  >> Yup.  We also want to eliminate the variables we don't actually use.  Gimpl
>  >e
>  >> likes to create lots of temporaries.  Many of them can goaway as a result
>  >> of our optimizers.
>  >> 
>  >
>  >And we know when we rewrite out of SSA exactly which ones have been
>  >used. In fact, the out_of_ssa_tag has been set on all variables which
>  >are actually used in the function. Anything not set hasn't been
>  >referenced.
> What about variables which only appear in VUSE/VDEFs -- like variables
> used/set by asms?

Well, those have the out_of_ssa_tag set if they are referenced in a PHI
node. 

> 
> So what I do is set my used bit during the walk over the tree structures
> that occurs in create_ssa_var_map.    At first I only marked variables
> which appeared as a use or def.  But I quickly ran into variables which
> appeared only in vuse/vdefs such as operands to asms, so I have to walk
> and mark the virtual operands as well.
> 

The out_of_ssa_tag will be set on anything that went through the
partitioning process. That amounts to anything which is a USE, a DEF, or
occurs in a PHI node somewhere. I guess its possible that there will be
variables which are used like this, but not in the partition map. I
suppose you can have all ASM VDEF's added to the partition during
create_ssa_var_map... then they'd have that bit set for sure.

Andrew