RFA: Fix PR middle-end/59049

[Eric Botcazou]

> In this case it's fold-all-builtins folding a strlen call with a
> PHI <"foo", "bar"> argument.  IMHO not presenting RTL with such
> non-sense is best achieved by not letting TER do constant propagation
> (because it doesn't "fold" the result).  We can never rule out such
> stray non-propagated constants, so that makes expand more robust
> (and hopes for RTL CCP).
> 
> Index: gcc/tree-ssa-ter.c
> ===================================================================
> --- gcc/tree-ssa-ter.c  (revision 204664)
> +++ gcc/tree-ssa-ter.c  (working copy)
> @@ -438,6 +439,12 @@ ter_is_replaceable_p (gimple stmt)
>           && !is_gimple_val (gimple_assign_rhs1 (stmt)))
>         return false;
> 
> +      /* Do not propagate "modeless" constants - we may end up
> confusing the RTL
> +        expanders.  Leave the optimization to RTL CCP.  */
> +      if (gimple_assign_single_p (stmt)
> +         && CONSTANT_CLASS_P (gimple_assign_rhs1 (stmt)))
> +       return false;
> +
>        return true;
>      }
>    return false;
> 
> does that make sense?  I'll test it then.

I agree with Joern that we want more constant propagation/folding during 
RTL expansion, not less, so IMO that's the wrong direction.

-- 
Eric Botcazou