Richard Guenther wrote:
> On Fri, 5 Aug 2011, Martin Jambor wrote:
> > the patch below fixes PR 49923 by checking for misaligned accesses
> > before doing IPA-SRA (on strict alignment targets). I have checked it
> > fixes the issue on compile farm sparc64 and I also included this in a
> > bootstrap and testsuite run on an x86_64-linux just to double check.
> >
> > OK for trunk and the 4.6 branch?
>
> Ok for now.
>
> I think we need to move this to generic middle-end code and also
> do something about partly strict-alignment targets such as x86_64.
> Iff expansion would treat expr as if it had non-natural alignment
> then when building a MEM_REF replacement with non-BLKmode we have
> to use a properly aligned variant type for it.
>
> I think we can trick FRE/PRE to run into exactly the same situation.
>
> I'll put it on my TODO.
This caused new failures on spu-elf:
FAIL: gcc.dg/ipa/ipa-sra-2.c scan-tree-dump eipa_sra "About to replace expr
cow_.*D.->red with \\*ISRA"
FAIL: gcc.dg/ipa/ipa-sra-2.c scan-tree-dump eipa_sra "About to replace expr
cow_.*D.->green with ISRA"
FAIL: gcc.dg/ipa/ipa-sra-2.c scan-tree-dump eipa_sra "About to replace expr
calf_.*D.->red with \\*ISRA"
FAIL: gcc.dg/ipa/ipa-sra-2.c scan-tree-dump eipa_sra "About to replace expr
calf_.*D.->green with ISRA"
FAIL: gcc.dg/ipa/ipa-sra-6.c scan-tree-dump-times eipa_sra "foo " 1
Looking at the last case, tree_non_mode_aligned_mem_p gets called with
expressions like those:
<component_ref 0xf6f4da40
type <pointer_type 0xf6f602a0
type <record_type 0xf6f60180 bovid sizes-gimplified type_0 BLK
size <integer_cst 0xf6f4d680 constant 96>
unit size <integer_cst 0xf6f4d6c0 constant 12>
align 32 symtab 0 alias set 2 canonical type 0xf6f60180 fields
<field_decl 0xf6f601e0 a> context <translation_unit_decl 0xf6ec10a0 D.2004>
pointer_to_this <pointer_type 0xf6f602a0> chain <type_decl
0xf6ec1030 D.1991>>
sizes-gimplified public unsigned SI
size <integer_cst 0xf6e10580 constant 32>
unit size <integer_cst 0xf6e105a0 constant 4>
align 32 symtab 0 alias set 5 canonical type 0xf6f602a0>
arg 0 <mem_ref 0xf6f4da60 type <record_type 0xf6f60180 bovid>
arg 0 <ssa_name 0xf6f0ccf0 type <pointer_type 0xf6f602a0>
visited var <parm_decl 0xf6f70000 cow>def_stmt GIMPLE_NOP
version 3
ptr-info 0xf6e760d0>
arg 1 <integer_cst 0xf6f4d7a0 constant 0>
/home/uweigand/fsf/gcc-head/gcc/testsuite/gcc.dg/ipa/ipa-sra-6.c:16:10>
arg 1 <field_decl 0xf6f60300 next type <pointer_type 0xf6f602a0>
unsigned SI file
/home/uweigand/fsf/gcc-head/gcc/testsuite/gcc.dg/ipa/ipa-sra-6.c line 8 col 17
size <integer_cst 0xf6e10580 32> unit size <integer_cst 0xf6e105a0 4>
align 32 offset_align 128
offset <integer_cst 0xf6e105c0 constant 0>
bit offset <integer_cst 0xf6e10620 constant 64> context <record_type
0xf6f60180 bovid>>
/home/uweigand/fsf/gcc-head/gcc/testsuite/gcc.dg/ipa/ipa-sra-6.c:16:10>
Now, the component reference as such doesn't introduce any misalignment;
there are no attribute-aligned in place anywhere.
However, the ptr-info of the "cow" parameter is set up to assume nothing
about alignment. Therefore, get_object_alignment returns 8, and
tree_non_mode_aligned_mem_p then of course fails.
I must admin I continue to be confused about exactly what it is that
tree_non_mode_aligned_mem_p is supposed to be testing for. We have:
if (TREE_CODE (exp) == SSA_NAME
|| TREE_CODE (exp) == MEM_REF
|| mode == BLKmode
|| is_gimple_min_invariant (exp)
|| !STRICT_ALIGNMENT)
return false;
So if we passed in the plain MEM_REF, this would be considered no problem.
The COMPONENT_REF does not add any additional misalignment, so one would
hope that this also shouldn't be a problem.
However, just because there *is* a COMPONENT_REF around it, we suddenly
realize the fact that don't have points-to information for the MEM_REF
and therefore consider *it* (and consequently the whole COMPONENT_REF)
to be potentially misaligned ...
Bye,
Ulrich
--
Dr. Ulrich Weigand
GNU Toolchain for Linux on System z and Cell BE
[email protected]
