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Re: [PATCH, rs6000] [v2] Folding of vector loads in GIMPLE
On Thu, Sep 14, 2017 at 4:38 PM, Bill Schmidt
<wschmidt@linux.vnet.ibm.com> wrote:
> On Sep 14, 2017, at 5:15 AM, Richard Biener <richard.guenther@gmail.com> wrote:
>>
>> On Wed, Sep 13, 2017 at 10:14 PM, Bill Schmidt
>> <wschmidt@linux.vnet.ibm.com> wrote:
>>> On Sep 13, 2017, at 10:40 AM, Bill Schmidt <wschmidt@linux.vnet.ibm.com> wrote:
>>>>
>>>> On Sep 13, 2017, at 7:23 AM, Richard Biener <richard.guenther@gmail.com> wrote:
>>>>>
>>>>> On Tue, Sep 12, 2017 at 11:08 PM, Will Schmidt
>>>>> <will_schmidt@vnet.ibm.com> wrote:
>>>>>> Hi,
>>>>>>
>>>>>> [PATCH, rs6000] [v2] Folding of vector loads in GIMPLE
>>>>>>
>>>>>> Folding of vector loads in GIMPLE.
>>>>>>
>>>>>> Add code to handle gimple folding for the vec_ld builtins.
>>>>>> Remove the now obsoleted folding code for vec_ld from rs6000-c.c. Surrounding
>>>>>> comments have been adjusted slightly so they continue to read OK for the
>>>>>> existing vec_st code.
>>>>>>
>>>>>> The resulting code is specifically verified by the powerpc/fold-vec-ld-*.c
>>>>>> tests which have been posted separately.
>>>>>>
>>>>>> For V2 of this patch, I've removed the chunk of code that prohibited the
>>>>>> gimple fold from occurring in BE environments. This had fixed an issue
>>>>>> for me earlier during my development of the code, and turns out this was
>>>>>> not necessary. I've sniff-tested after removing that check and it looks
>>>>>> OK.
>>>>>>
>>>>>>> + /* Limit folding of loads to LE targets. */
>>>>>>> + if (BYTES_BIG_ENDIAN || VECTOR_ELT_ORDER_BIG)
>>>>>>> + return false;
>>>>>>
>>>>>> I've restarted a regression test on this updated version.
>>>>>>
>>>>>> OK for trunk (assuming successful regression test completion) ?
>>>>>>
>>>>>> Thanks,
>>>>>> -Will
>>>>>>
>>>>>> [gcc]
>>>>>>
>>>>>> 2017-09-12 Will Schmidt <will_schmidt@vnet.ibm.com>
>>>>>>
>>>>>> * config/rs6000/rs6000.c (rs6000_gimple_fold_builtin): Add handling
>>>>>> for early folding of vector loads (ALTIVEC_BUILTIN_LVX_*).
>>>>>> * config/rs6000/rs6000-c.c (altivec_resolve_overloaded_builtin):
>>>>>> Remove obsoleted code for handling ALTIVEC_BUILTIN_VEC_LD.
>>>>>>
>>>>>> diff --git a/gcc/config/rs6000/rs6000-c.c b/gcc/config/rs6000/rs6000-c.c
>>>>>> index fbab0a2..bb8a77d 100644
>>>>>> --- a/gcc/config/rs6000/rs6000-c.c
>>>>>> +++ b/gcc/config/rs6000/rs6000-c.c
>>>>>> @@ -6470,92 +6470,19 @@ altivec_resolve_overloaded_builtin (location_t loc, tree fndecl,
>>>>>> convert (TREE_TYPE (stmt), arg0));
>>>>>> stmt = build2 (COMPOUND_EXPR, arg1_type, stmt, decl);
>>>>>> return stmt;
>>>>>> }
>>>>>>
>>>>>> - /* Expand vec_ld into an expression that masks the address and
>>>>>> - performs the load. We need to expand this early to allow
>>>>>> + /* Expand vec_st into an expression that masks the address and
>>>>>> + performs the store. We need to expand this early to allow
>>>>>> the best aliasing, as by the time we get into RTL we no longer
>>>>>> are able to honor __restrict__, for example. We may want to
>>>>>> consider this for all memory access built-ins.
>>>>>>
>>>>>> When -maltivec=be is specified, or the wrong number of arguments
>>>>>> is provided, simply punt to existing built-in processing. */
>>>>>> - if (fcode == ALTIVEC_BUILTIN_VEC_LD
>>>>>> - && (BYTES_BIG_ENDIAN || !VECTOR_ELT_ORDER_BIG)
>>>>>> - && nargs == 2)
>>>>>> - {
>>>>>> - tree arg0 = (*arglist)[0];
>>>>>> - tree arg1 = (*arglist)[1];
>>>>>> -
>>>>>> - /* Strip qualifiers like "const" from the pointer arg. */
>>>>>> - tree arg1_type = TREE_TYPE (arg1);
>>>>>> - if (!POINTER_TYPE_P (arg1_type) && TREE_CODE (arg1_type) != ARRAY_TYPE)
>>>>>> - goto bad;
>>>>>> -
>>>>>> - tree inner_type = TREE_TYPE (arg1_type);
>>>>>> - if (TYPE_QUALS (TREE_TYPE (arg1_type)) != 0)
>>>>>> - {
>>>>>> - arg1_type = build_pointer_type (build_qualified_type (inner_type,
>>>>>> - 0));
>>>>>> - arg1 = fold_convert (arg1_type, arg1);
>>>>>> - }
>>>>>> -
>>>>>> - /* Construct the masked address. Let existing error handling take
>>>>>> - over if we don't have a constant offset. */
>>>>>> - arg0 = fold (arg0);
>>>>>> -
>>>>>> - if (TREE_CODE (arg0) == INTEGER_CST)
>>>>>> - {
>>>>>> - if (!ptrofftype_p (TREE_TYPE (arg0)))
>>>>>> - arg0 = build1 (NOP_EXPR, sizetype, arg0);
>>>>>> -
>>>>>> - tree arg1_type = TREE_TYPE (arg1);
>>>>>> - if (TREE_CODE (arg1_type) == ARRAY_TYPE)
>>>>>> - {
>>>>>> - arg1_type = TYPE_POINTER_TO (TREE_TYPE (arg1_type));
>>>>>> - tree const0 = build_int_cstu (sizetype, 0);
>>>>>> - tree arg1_elt0 = build_array_ref (loc, arg1, const0);
>>>>>> - arg1 = build1 (ADDR_EXPR, arg1_type, arg1_elt0);
>>>>>> - }
>>>>>> -
>>>>>> - tree addr = fold_build2_loc (loc, POINTER_PLUS_EXPR, arg1_type,
>>>>>> - arg1, arg0);
>>>>>> - tree aligned = fold_build2_loc (loc, BIT_AND_EXPR, arg1_type, addr,
>>>>>> - build_int_cst (arg1_type, -16));
>>>>>> -
>>>>>> - /* Find the built-in to get the return type so we can convert
>>>>>> - the result properly (or fall back to default handling if the
>>>>>> - arguments aren't compatible). */
>>>>>> - for (desc = altivec_overloaded_builtins;
>>>>>> - desc->code && desc->code != fcode; desc++)
>>>>>> - continue;
>>>>>> -
>>>>>> - for (; desc->code == fcode; desc++)
>>>>>> - if (rs6000_builtin_type_compatible (TREE_TYPE (arg0), desc->op1)
>>>>>> - && (rs6000_builtin_type_compatible (TREE_TYPE (arg1),
>>>>>> - desc->op2)))
>>>>>> - {
>>>>>> - tree ret_type = rs6000_builtin_type (desc->ret_type);
>>>>>> - if (TYPE_MODE (ret_type) == V2DImode)
>>>>>> - /* Type-based aliasing analysis thinks vector long
>>>>>> - and vector long long are different and will put them
>>>>>> - in distinct alias classes. Force our return type
>>>>>> - to be a may-alias type to avoid this. */
>>>>>> - ret_type
>>>>>> - = build_pointer_type_for_mode (ret_type, Pmode,
>>>>>> - true/*can_alias_all*/);
>>>>>> - else
>>>>>> - ret_type = build_pointer_type (ret_type);
>>>>>> - aligned = build1 (NOP_EXPR, ret_type, aligned);
>>>>>> - tree ret_val = build_indirect_ref (loc, aligned, RO_NULL);
>>>>>> - return ret_val;
>>>>>> - }
>>>>>> - }
>>>>>> - }
>>>>>>
>>>>>> - /* Similarly for stvx. */
>>>>>> if (fcode == ALTIVEC_BUILTIN_VEC_ST
>>>>>> && (BYTES_BIG_ENDIAN || !VECTOR_ELT_ORDER_BIG)
>>>>>> && nargs == 3)
>>>>>> {
>>>>>> tree arg0 = (*arglist)[0];
>>>>>> diff --git a/gcc/config/rs6000/rs6000.c b/gcc/config/rs6000/rs6000.c
>>>>>> index 1338371..1fb5f44 100644
>>>>>> --- a/gcc/config/rs6000/rs6000.c
>>>>>> +++ b/gcc/config/rs6000/rs6000.c
>>>>>> @@ -16547,10 +16547,61 @@ rs6000_gimple_fold_builtin (gimple_stmt_iterator *gsi)
>>>>>> res = gimple_build (&stmts, VIEW_CONVERT_EXPR, TREE_TYPE (lhs), res);
>>>>>> gsi_insert_seq_before (gsi, stmts, GSI_SAME_STMT);
>>>>>> update_call_from_tree (gsi, res);
>>>>>> return true;
>>>>>> }
>>>>>> + /* Vector loads. */
>>>>>> + case ALTIVEC_BUILTIN_LVX_V16QI:
>>>>>> + case ALTIVEC_BUILTIN_LVX_V8HI:
>>>>>> + case ALTIVEC_BUILTIN_LVX_V4SI:
>>>>>> + case ALTIVEC_BUILTIN_LVX_V4SF:
>>>>>> + case ALTIVEC_BUILTIN_LVX_V2DI:
>>>>>> + case ALTIVEC_BUILTIN_LVX_V2DF:
>>>>>> + {
>>>>>> + gimple *g;
>>>>>> + arg0 = gimple_call_arg (stmt, 0); // offset
>>>>>> + arg1 = gimple_call_arg (stmt, 1); // address
>>>>>> +
>>>>>> + lhs = gimple_call_lhs (stmt);
>>>>>> + location_t loc = gimple_location (stmt);
>>>>>> +
>>>>>> + tree arg1_type = TREE_TYPE (arg1);
>>>>>> + tree lhs_type = TREE_TYPE (lhs);
>>>>>> +
>>>>>> + /* POINTER_PLUS_EXPR wants the offset to be of type 'sizetype'. Create
>>>>>> + the tree using the value from arg0. The resulting type will match
>>>>>> + the type of arg1. */
>>>>>> + tree temp_offset = create_tmp_reg_or_ssa_name (sizetype);
>>>>>> + g = gimple_build_assign (temp_offset, NOP_EXPR, arg0);
>>>>>> + gimple_set_location (g, loc);
>>>>>> + gsi_insert_before (gsi, g, GSI_SAME_STMT);
>>>>>> + tree temp_addr = create_tmp_reg_or_ssa_name (arg1_type);
>>>>>> + g = gimple_build_assign (temp_addr, POINTER_PLUS_EXPR, arg1,
>>>>>> + temp_offset);
>>>>>> + gimple_set_location (g, loc);
>>>>>> + gsi_insert_before (gsi, g, GSI_SAME_STMT);
>>>>>> +
>>>>>> + /* Mask off any lower bits from the address. */
>>>>>> + tree alignment_mask = build_int_cst (arg1_type, -16);
>>>>>> + tree aligned_addr = create_tmp_reg_or_ssa_name (arg1_type);
>>>>>> + g = gimple_build_assign (aligned_addr, BIT_AND_EXPR,
>>>>>> + temp_addr, alignment_mask);
>>>>>> + gimple_set_location (g, loc);
>>>>>> + gsi_insert_before (gsi, g, GSI_SAME_STMT);
>>>>>
>>>>> You could use
>>>>>
>>>>> gimple_seq stmts = NULL;
>>>>> tree temp_offset = gimple_convert (&stmts, loc, sizetype, arg0);
>>>>> tree temp_addr = gimple_build (&stmts, loc, POINTER_PLUS_EXPR,
>>>>> arg1_type, arg1, temp_offset);
>>>>> tree aligned_addr = gimple_build (&stmts, loc, BIT_AND_EXPR,
>>>>> arg1_type, temp_addr, build_int_cst (arg1_type, -16));
>>>>> gsi_insert_seq_before (gsi, stmts, GSI_SAME_STMT);
>>>>>
>>>>>> + /* Use the build2 helper to set up the mem_ref. The MEM_REF could also
>>>>>> + take an offset, but since we've already incorporated the offset
>>>>>> + above, here we just pass in a zero. */
>>>>>> + g = gimple_build_assign (lhs, build2 (MEM_REF, lhs_type, aligned_addr,
>>>>>> + build_int_cst (arg1_type, 0)));
>>>>>
>>>>> are you sure about arg1_type here? I'm sure not. For
>>>>>
>>>>> ... foo (struct S *p)
>>>>> {
>>>>> return __builtin_lvx_v2df (4, (double *)p);
>>>>> }
>>>>>
>>>>> you'd end up with p as arg1 and thus struct S * as arg1_type and thus
>>>>> TBAA using 'struct S' to access the memory.
>>>>
>>>> Hm, is that so? Wouldn't arg1_type be double* since arg1 is (double *)p?
>>>> Will, you should probably test this example and see, but I'm pretty confident
>>>> about this (see below).
>>>
>>> But, as I should have suspected, you're right. For some reason
>>> gimple_call_arg is returning p, stripped of the cast information where the
>>> user asserted that p points to a double*.
>>>
>>> Can you explain to me why this should be so? I assume that somebody
>>> has decided to strip_nops the argument and lose the cast.
>>
>> pointer types have no meaning in GIMPLE so we aggressively prune them.
>>
>>> Using ptr_type_node loses all type information, so that would be a
>>> regression from what we do today. In some cases we could reconstruct
>>> that this was necessarily, say, a double*, but I don't know how we would
>>> recover the signedness for an integer type.
>>
>> How did we handle the expansion previously - ah - it was done earlier
>> in the C FE. So why are you moving it to GIMPLE? The function is called
>> resolve_overloaded_builtin - what kind of overloading do you resolve here?
>> As said argument types might not be preserved.
>
> The AltiVec builtins allow overloaded names based on the argument types,
> using a special callout during parsing to convert the overloaded names to
> type-specific names. Historically these have then remained builtin calls
> until RTL expansion, which loses a lot of useful optimization. Will has been
> gradually implementing gimple folding for these builtins so that we can
> optimize simple vector arithmetic and so on. The overloading is still dealt
> with during parsing.
>
> As an example:
>
> double a[64];
> vector double x = vec_ld (0, a);
>
> will get translated into
>
> vector double x = __builtin_altivec_lvx_v2df (0, a);
>
> and
>
> unsigned char b[64];
> vector unsigned char y = vec_ld (0, b);
>
> will get translated into
>
> vector unsigned char y = __builtin_altivec_lvx_v16qi (0, b);
>
> So in resolving the overloading we still maintain the type info for arg1.
So TBAA-wise the vec_ld is specced to use alias-set zero for this case
as it loads from a unsinged char array? Or is it alias-set zero because
the type of arg1 is unsigned char *? What if the type of arg1 was
struct X *?
> Earlier I had dealt with the performance issue in a different way for the
> vec_ld and vec_st overloaded builtins, which created the rather grotty
> code in rs6000-c.c to modify the parse trees instead. My hope was that
> we could simplify the code by having Will deal with them as gimple folds
> instead. But if in so doing we lose type information, that may not be the
> right call.
>
> However, since you say that gimple aggressively removes the casts
> from pointer types, perhaps the code that we see in early gimple from
> the existing method might also be missing the type information? Will,
> it would be worth looking at that code to see. If it's no different then
> perhaps we still go ahead with the folding.
As I said you can't simply use the type of arg1 for the TBAA type.
You can conservatively use ptr_type_node (alias-set zero) or you
can use sth that you derive from the builtin used (is a supposedly
existing _v4si variant always subject to int * TBAA?)
> Another note for Will: The existing code gives up when -maltivec=be has
> been specified, and you probably want to do that as well. That may be
> why you initially turned off big endian -- it is easy to misread that code.
> -maltivec=be is VECTOR_ELT_ORDER_BIG && !BYTES_BIG_ENDIAN.
>
> Thanks,
> Bill
>>
>> Richard.
>>
>>> Bill
>>>>
>>>>>
>>>>> I think if the builtins have any TBAA constraints you need to build those
>>>>> explicitely, if not, you should use ptr_type_node aka no TBAA.
>>>>
>>>> The type signatures are constrained during parsing, so we should only
>>>> see allowed pointer types on arg1 by the time we get to gimple folding. I
>>>> think that using arg1_type should work, but I am probably missing
>>>> something subtle, so please feel free to whack me on the temple until
>>>> I get it. :-)
>>>>
>>>> Bill
>>>>>
>>>>> Richard.
>>>>>
>>>>>> + gimple_set_location (g, loc);
>>>>>> + gsi_replace (gsi, g, true);
>>>>>> +
>>>>>> + return true;
>>>>>> +
>>>>>> + }
>>>>>> +
>>>>>> default:
>>>>>> if (TARGET_DEBUG_BUILTIN)
>>>>>> fprintf (stderr, "gimple builtin intrinsic not matched:%d %s %s\n",
>>>>>> fn_code, fn_name1, fn_name2);
>>>>>> break;
>