On Thu, 11 Oct 2012, Jan Hubicka wrote:
> Hi,
> this patch address problem I run into with strenghtened cunroll pass. I made
> cunroll to use loop_max_iterations bounds into an account that makes us to
> occasionally produce out of bounds loop accesses in loop like:
>
> for (i=0;i<n;i++)
> {
> <something>
> if (test)
> break
> a[i]=1;
> }
> Here the constantly sized array appears in loop with multiple exits and we
> then
> in the last iteration produce out of bound array (since we need to duplicate
> <something> and tree-ssa-vrp warns.
>
> I think this is more generic problem (though appearing rarely): as soon as we
> specialize the code, we can no longer warn about out of bounds accesses when
> we
> prove array ref to be constant. We have no idea if this code path will
> execute
> in practice.
>
> Seems resonable? I think similar problems can be constructed by inlining,
> too.
> Regtested/bootstrapped x86_64-linux.
No, I don't think this is reasonable. There are other PRs for this
as well, btw.
The array-bounds warning in VRP needs to be conditional if the
path to it isn't always executed, too (thus a may-be warning).
Richard.
> Honza
>
> * tree-cfg.c (gimple_duplicate_bb): Drop NO_WARNING on array refs.
> Index: tree-cfg.c
> ===================================================================
> *** tree-cfg.c (revision 192360)
> --- tree-cfg.c (working copy)
> *************** gimple_duplicate_bb (basic_block bb)
> *** 5504,5509 ****
> --- 5504,5519 ----
> if (lhs && TREE_CODE (lhs) != SSA_NAME)
> {
> tree base = get_base_address (lhs);
> + tree op = lhs;
> +
> + /* Silence the array bounds warning. After specializing the code we
> + no longer know if the particular code path can execute at runtime.
> */
> + while (handled_component_p (op))
> + {
> + if (TREE_CODE (op) == ARRAY_REF)
> + TREE_NO_WARNING (op) = 1;
> + op = TREE_OPERAND (op, 0);
> + }
> if (base
> && (TREE_CODE (base) == VAR_DECL
> || TREE_CODE (base) == RESULT_DECL)
> *************** gimple_duplicate_bb (basic_block bb)
> *** 5514,5519 ****
> --- 5521,5539 ----
> || !DECL_HAS_VALUE_EXPR_P (base)))
> DECL_NONSHAREABLE (base) = 1;
> }
> +
> + /* Silence the array bounds warning. After specializing the code we
> + no longer know if the particular code path can execute at runtime.
> */
> + if (gimple_code (stmt) == GIMPLE_ASSIGN)
> + {
> + tree op = gimple_assign_rhs1 (stmt);
> + while (handled_component_p (op))
> + {
> + if (TREE_CODE (op) == ARRAY_REF)
> + TREE_NO_WARNING (op) = 1;
> + op = TREE_OPERAND (op, 0);
> + }
> + }
>
> /* Create new names for all the definitions created by COPY and
> add replacement mappings for each new name. */
>
>
--
Richard Biener <rguent...@suse.de>
SUSE / SUSE Labs
SUSE LINUX Products GmbH - Nuernberg - AG Nuernberg - HRB 16746
GF: Jeff Hawn, Jennifer Guild, Felix Imend
