On Mon, Aug 27, 2018 at 10:31 PM Jeff Law <l...@redhat.com> wrote:
>
>
> We recently changes tree-ssa-dse.c to not trim stores outside the bounds
> of the referenced object. This is generally a good thing.
>
> However, there are cases where the object doesn't have a usable size.
> We see this during kernel builds, at least on the microblaze target.
>
> We've got...
>
> _1 = p_47(D)->stack;
> childregs_48 = &MEM[(void *)_1 + 8040B];
> [ ... ]
> memset (childregs_48, 0, 152);
> [ ... ]
> MEM[(struct pt_regs *)_1 + 8040B].pt_mode = 1;
>
>
> We want to trim the memset call as the assignment to pt_mode is the last
> word written by the memset call, thus making the store of that word via
> memset dead.
>
> Our ref->base is:
>
> (gdb) p debug_tree ($66)
> <mem_ref 0x7fffe8b946e0
> type <void_type 0x7fffe9e210a8 void VOID
> align:8 warn_if_not_align:0 symtab:0 alias-set -1 canonical-type
> 0x7fffe9e210a8
> pointer_to_this <pointer_type 0x7fffe9e21150>>
>
> arg:0 <ssa_name 0x7fffe8f8a2d0
> type <pointer_type 0x7fffe9e21150 type <void_type 0x7fffe9e210a8
> void>
> public unsigned SI
> size <integer_cst 0x7fffe9e0d678 constant 32>
> unit-size <integer_cst 0x7fffe9e0d690 constant 4>
> align:32 warn_if_not_align:0 symtab:0 alias-set 8
> canonical-type 0x7fffe9e21150 context <translation_unit_decl
> 0x7fffe8f72438 /tmp/process.i>
> pointer_to_this <pointer_type 0x7fffe9e28bd0>
> reference_to_this <reference_type 0x7fffe9e282a0>>
> visited
> def_stmt _1 = p_47(D)->stack;
> version:1
> ptr-info 0x7fffe8f65fa8>
> arg:1 <integer_cst 0x7fffe8f65f60 type <pointer_type 0x7fffe9e21150>
> constant 8040>>
>
>
> Note the void type. Those do not have a suitable TYPE_SIZE_UNIT, thus
> causing an ICE when we try to reference it within compute_trims:
> /* But don't trim away out of bounds accesses, as this defeats
> proper warnings. */
> if (*trim_tail
> && compare_tree_int (TYPE_SIZE_UNIT (TREE_TYPE (ref->base)),
> last_orig) <= 0)
>
>
> The fix is obvious enough. Don't do the check when the underlying type
> has no usable TYPE_SIZE_UNIT.
>
> I pondered moving the tests into the code that determines whether or not
> we do byte tracking DSE, but decided the current location was fine.
>
> Bootstrapped and regression tested on x86. Also verified the original
> testfile will build with a microblaze cross compiler.
>
> Installing on the trunk momentarily.
Hmm, you seem to get ref->base from an address but you know types
on addresses do not have any meaning, so ... how does
/* But don't trim away out of bounds accesses, as this defeats
proper warnings.
We could have a type with no TYPE_SIZE_UNIT or we could have a VLA
where TYPE_SIZE_UNIT is not a constant. */
if (*trim_tail
&& TYPE_SIZE_UNIT (TREE_TYPE (ref->base))
&& TREE_CODE (TYPE_SIZE_UNIT (TREE_TYPE (ref->base))) == INTEGER_CST
&& compare_tree_int (TYPE_SIZE_UNIT (TREE_TYPE (ref->base)),
last_orig) <= 0)
*trim_tail = 0;
make any sense in the above case where ref->base is even based on a
pointer? I'd say the
above should be at least
if (*trim_tail
&& DECL_P (ref->base)
&& ....
? Not sure if we ever have decls with incomplete types so eventually
the new check
isn't needed.
Richard.
> jeff
