Re: [PATCH] PR tree-optimization/109417 - Check if dependency is valid before using in may_recompute_p.

[Jakub Jelinek <jakub@redhat.com>]

On Wed, Apr 05, 2023 at 04:10:25PM -0400, Andrew MacLeod via Gcc-patches wrote:
> When a statement is first processed, any SSA_NAMEs that are dependencies are
> cached for quick future access.
> 
> if we ;later rewrite the statement (say propagate a constant into it), its
> possible the ssa-name in this cache is no longer active.   Normally this is
> not a problem, but the changed to may_recompute_p forgot to take that into
> account, and was checking a dependency from the cache that was in the
> SSA_NAME_FREE_LIST. It thus had no SSA_NAME_DEF_STMT when we were expecting
> one.
> 
> This patch simply rejects dependencies from consideration if they are in the
> free list.
> 
> Bootstrapping on x86_64-pc-linux-gnu  and presuming no regressio0ns, OK for
> trunk?
> 
> Andrew

> commit ecd86e159e8499feb387bc4d99bd37a5fd6a0d68
> Author: Andrew MacLeod <amacleod@redhat.com>
> Date:   Wed Apr 5 15:59:38 2023 -0400
> 
>     Check if dependency is valid before using in may_recompute_p.
>     
>     When the IL is rewritten after a statement has been processed and
>     dependencies cached, its possible that an ssa-name in the dependency
>     cache is no longer in the IL.  Check this before trying to recompute.
>     
>             PR tree-optimization/109417
>             gcc/
>             * gimple-range-gori.cc (gori_compute::may_recompute_p): Check if
>             dependency is in SSA_NAME_FREE_LIST.
>     
>             gcc/testsuite/
>             * gcc.dg/pr109417.c: New.

Ok for trunk (mainly to unbreak the recent regression).
But please be ready to adjust if Richi disagrees next week.

> --- a/gcc/gimple-range-gori.cc
> +++ b/gcc/gimple-range-gori.cc
> @@ -1314,7 +1314,9 @@ gori_compute::may_recompute_p (tree name, basic_block bb, int depth)
>    tree dep2 = depend2 (name);
>  
>    // If the first dependency is not set, there is no recomputation.
> -  if (!dep1)
> +  // Dependencies reflect original IL, not current state.   Check if the
> +  // SSA_NAME is still valid as well.
> +  if (!dep1 || SSA_NAME_IN_FREE_LIST (dep1))
>      return false;
>  
>    // Don't recalculate PHIs or statements with side_effects.

	Jakub