Re: Deadly optimization bug (all gcc versions!)

[Franz Sirl <Franz.Sirl-kernel@lauterbach.com>]

At 10:37 30.08.99 , Jeffrey A Law wrote:

>   In message <4.2.0.58.19990830094306.047fd8c0@mail.lauterbach.com>you write:
>   > At 16:14 24.08.99 , Bernd Schmidt wrote:
>   > >+      /* We can't do anything if the value is set in between the 
> insns we
>   >  are
>   > >+       processing.  */
>   > >+      if (INSN_CUID (reg_last_set[regno]) <= INSN_CUID (subst_insn))
>   > >+       return 0;
>   > >+
>   >
>   > Just for my understanding, reg_last_set[regno] will not point past
>   > subst_insn here? What I'm thinking about is, what happens if we have 
> 3 SETs
>   >
>   > like:
>   >
>   > SET1
>   > start_of_subst_tree
>   > ...
>   > SET2
>   > ...
>   > subst_insn
>   > ...
>   > SET3
>   >
>   > Will reg_last_set[] point to SET2 or SET3? If it points to SET3, your 
> patch
>   > doesn't cover all possibilities, or?
>I don't think reg_last_set can point to set3 since we haven't processed
>anything beyond subst_insn yet.
>
>It can point to SET2, which is the case Bernd's patch is dealing with.

Ah, ok. Thanks for the clarification. I was under the impression all this 
reg_* arrays were computed at the start of combine for the whole function 
and then updated on-the-fly during combine.

Franz.