[RFC] PR64703, glibc sysdeps/powerpc/powerpc64/dl-machine.h miscompile
Richard Biener
richard.guenther@gmail.com
Mon Jan 26 09:56:00 GMT 2015
On Sat, Jan 24, 2015 at 12:23 AM, Alan Modra <amodra@gmail.com> wrote:
> How does this look as a potential fix for PR64703? I haven't made
> many forays into gimple code, so even though this patch passes
> bootstrap and regression testing on powerpc64-linux it's quite
> possible this is the wrong place to change. If it does look to be OK,
> then I'll fill out the targetm changes, include a testcase etc.
It looks mostly ok, comments below.
> PR target/64703
> * tree-ssa-alias.c (pt_solution_includes_base): New function,
> extracted from..
> (ref_maybe_used_by_call_p_1): ..here. Delete dead code checking
> for NULL return from ao_ref_base. Handle potential memory
> reference by indirect calls on targets using function descriptors.
>
> Index: gcc/tree-ssa-alias.c
> ===================================================================
> --- gcc/tree-ssa-alias.c (revision 220025)
> +++ gcc/tree-ssa-alias.c (working copy)
> @@ -1532,6 +1532,23 @@ refs_output_dependent_p (tree store1, tree store2)
> return refs_may_alias_p_1 (&r1, &r2, false);
> }
>
> +static bool
> +pt_solution_includes_base (struct pt_solution *pt, tree base)
Needs a comment.
> +{
> + if (DECL_P (base))
> + return pt_solution_includes (pt, base);
> +
> + if ((TREE_CODE (base) == MEM_REF
> + || TREE_CODE (base) == TARGET_MEM_REF)
> + && TREE_CODE (TREE_OPERAND (base, 0)) == SSA_NAME)
> + {
> + struct ptr_info_def *pi = SSA_NAME_PTR_INFO (TREE_OPERAND (base, 0));
> + if (pi)
> + return pt_solutions_intersect (pt, &pi->pt);
> + }
> + return true;
> +}
> +
> /* If the call CALL may use the memory reference REF return true,
> otherwise return false. */
>
> @@ -1542,15 +1559,24 @@ ref_maybe_used_by_call_p_1 (gcall *call, ao_ref *r
> unsigned i;
> int flags = gimple_call_flags (call);
>
> + base = ao_ref_base (ref);
You dropped the
if (!base)
return true;
check - please put it back.
> + callee = gimple_call_fn (call);
> + if (callee && TREE_CODE (callee) == SSA_NAME
Do we never propagate the address of a function descriptor here?
That is, can we generate a testcase like
descr fn;
<setup fn>
foo (&fn);
void foo (fn)
{
(*fn) (a, b);
}
and then inline foo so the call becomes
(*&fn) (a, b);
? We'd then still implicitely read from 'fn'. I also wonder whether
(and where!) we resolve such a descriptor reference to the actual
function on GIMPLE?
That is - don't you simply want to use
if (targetm.function_descriptors
&& ptr_deref_mayalias_ref_p_1 (callee, ref))
return true;
here?
Thanks,
Richard.
> + /* && targetm.function_descriptors */)
> + {
> + /* Handle indirect call. When a target defines the address of a
> + function as that of a function descriptor, then dereferencing
> + a function pointer implicitly references memory. */
> + struct ptr_info_def *pi = SSA_NAME_PTR_INFO (callee);
> + if (pi && pt_solution_includes_base (&pi->pt, base))
> + return true;
> + }
> +
> /* Const functions without a static chain do not implicitly use memory. */
> if (!gimple_call_chain (call)
> && (flags & (ECF_CONST|ECF_NOVOPS)))
> goto process_args;
>
> - base = ao_ref_base (ref);
> - if (!base)
> - return true;
> -
> /* A call that is not without side-effects might involve volatile
> accesses and thus conflicts with all other volatile accesses. */
> if (ref->volatile_p)
> @@ -1564,7 +1590,7 @@ ref_maybe_used_by_call_p_1 (gcall *call, ao_ref *r
> && !is_global_var (base))
> goto process_args;
>
> - callee = gimple_call_fndecl (call);
> + callee = gimple_call_addr_fndecl (callee);
>
> /* Handle those builtin functions explicitly that do not act as
> escape points. See tree-ssa-structalias.c:find_func_aliases
> @@ -1803,23 +1829,7 @@ ref_maybe_used_by_call_p_1 (gcall *call, ao_ref *r
> }
>
> /* Check if the base variable is call-used. */
> - if (DECL_P (base))
> - {
> - if (pt_solution_includes (gimple_call_use_set (call), base))
> - return true;
> - }
> - else if ((TREE_CODE (base) == MEM_REF
> - || TREE_CODE (base) == TARGET_MEM_REF)
> - && TREE_CODE (TREE_OPERAND (base, 0)) == SSA_NAME)
> - {
> - struct ptr_info_def *pi = SSA_NAME_PTR_INFO (TREE_OPERAND (base, 0));
> - if (!pi)
> - return true;
> -
> - if (pt_solutions_intersect (gimple_call_use_set (call), &pi->pt))
> - return true;
> - }
> - else
> + if (pt_solution_includes_base (gimple_call_use_set (call), base))
> return true;
>
> /* Inspect call arguments for passed-by-value aliases. */
>
> --
> Alan Modra
> Australia Development Lab, IBM
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