Thoughts on memcmp expansion (PR43052)

[Bernd Schmidt]

On 05/02/2016 02:52 PM, Richard Biener wrote:
> +struct pieces_addr
> +{
> ...
> +  void *m_cfndata;
> +public:
> +  pieces_addr (rtx, bool, by_pieces_constfn, void *);
>
> unless you strick private: somewhere the public: is redundant

Yeah, ideally I want to turn these into a classes rather than structs. 
Maybe that particular one can already be done, but I'm kind of wondering 
how far to take the C++ification of the other one.

> Index: gcc/tree-ssa-forwprop.c
> ===================================================================
> --- gcc/tree-ssa-forwprop.c     (revision 235474)
> +++ gcc/tree-ssa-forwprop.c     (working copy)
> @@ -1435,6 +1435,76 @@ simplify_builtin_call (gimple_stmt_itera
>              }
>          }
>         break;
> +
> +    case BUILT_IN_MEMCMP:
> +      {
>
> I think this doesn't belong in forwprop.  If we want to stick it into
> a pass rather than
> folding it should be in tree-ssa-strlen.c.

This part (and the other one you quoted) was essentially your prototype 
patch from PR52171. I can put it whereever you like, really.

> Note that we can handle size-1 memcmp even for ordered compares.

One would hope this doesn't occur very often...

> Jakub, where do you think this fits best?  Note that gimple-fold.c may
> not use immediate uses but would have to match this from the
> comparison (I still have to find a way to handle this in match.pd where
> the result expression contains virtual operands in the not toplevel stmt).


Bernd