On Tue, Oct 29, 2013 at 11:23 PM, Marc Glisse <marc.gli...@inria.fr> wrote: > On Tue, 29 Oct 2013, Jeff Law wrote: > >> Marc pointed out that the handling of various BUILT_IN_MEM* and >> BUILT_IN_STR* functions in tree-ssa-alias.c probably wasn't working as >> intended because the code wasn't prepared for a common return value from >> ao_ref_base, particularly returns of MEM_REFs. > > > Hmm, ao_ref_base is never a pointer, so I'd say the issue is really with > trying to use the SSA_NAME directly.
Yes. Note that the code tries to relate two pointers but one is a memory-reference (ao_ref_base) and one is either a SSA name pointer or the result of get_addr_base_and_unit_offset (a memory reference as well). >> This patch fixes the code to handle the trivial case of returning a >> MEM_REF and adds a simple testcase. There's probably a lot more that could >> be done here. > > > Thanks. > > I am not sure we want to keep the variable "base" that is either a decl/ref > (from get_addr_base_and_unit_offset) or a pointer (dest). We know which case > is which, but then forget it by storing both into base. Maybe something like > this would be more "type-safe". > > bool same = false; > if (TREE_CODE (dest) == ADDR_EXPR) > same = (ref_base == get_addr_base_and_unit_offset > (TREE_OPERAND (dest, 0), &offset)); > else if (TREE_CODE (dest) == SSA_NAME > && TREE_CODE (ref_base) == MEM_REF) && integer_zerop (TREE_OPERAND (ref_base, 1)) > same = (TREE_OPERAND (ref_base, 0) == dest); > if (same) > ... Btw, get_addr_base_and_unit_offset may also return an offsetted MEM_REF (from &MEM [p_3, 17] for example). As we are interested in pointers this could be handled by not requiring a memory reference but extracting the base address and offset, covering more cases. > By the way, I think the patch is fine as is, I am only discussing possible > follow-ups. Only slightly wrong-codish ;) Richard. > (see http://gcc.gnu.org/ml/gcc-patches/2013-10/txto0PQEYpiuz.txt for another > approach using ao_ref_init_from_ptr_and_size) > > -- > Marc Glisse
