On Sep 22, 2017, at 5:27 AM, Richard Biener <richard.guent...@gmail.com> wrote:
>
> On Thu, Sep 21, 2017 at 10:56 PM, Will Schmidt
> <will_schm...@vnet.ibm.com> wrote:
>> Hi,
>>
>> Folding of vector stores in GIMPLE.
>>
>> - Add code to handle gimple folding for the vec_st (vector store) builtins.
>> - Remove the now obsoleted folding code for vec_st from rs6000-c-c.
>>
>> There are two spots that I could use some feedback on.
>>
>> First -
>> An early exit remains in place prevent folding of statements that do not
>> have a LHS. To allow folding of the stores to get past the check, I have
>> added a helper function (rs6000_builtin_valid_without_lhs) that allows
>> those store intrinsics to proceed. I'm not sure the approach (or the name I
>> chose)
>> is the best choice, so I'll defer to recommendations on how to improve that.
>> :-)
It's fine, but please make the helper function static.
>>
>> Second -
>> This code (as-is) is subject to a TBAA related issue (similar to what was
>> noticed
>> in the gimple folding code for loads. As-is, with a testcase such as :
>>
>> void testst_struct1b (vector double vd1, long long ll1, struct S *p)
>> {
>> vec_st (vd1, ll1, (vector double *)p);
>> }
>>
>> will generate gimple that looks like:
>> MEM[(struct S *)D.3218] = vd1;
>>
>> If I rework the code, setting arg2_type to be ptr_type_node, i.e.
>> + tree arg2_type = TREE_TYPE (arg2);
>> to:
>> + tree arg2_type = ptr_type_node;
>>
>> the generated gimple then looks like
>> MEM[(void *)D.3218] = vd1;
>>
>> Which is probably OK, but I cannot say for certain. The generated .s
>> content is at least equivalent.
>
> It looks safe.
>
> The question I had is whether vec_st (vd1, ll1, (vector double *)p) is
> equivalent
> to *(vector double *)((char *)p + ll1) = vd1; from a TBAA perspective. Thus
> whether the type of the tird argument to vec_st defines the type of the access
> (in C standards meaning). If so then what we do now is pessimizing (but
> as you say previously (long long *) and (long *) were aliased together and
> you got wrong-code with aliasing with regular stores of the "wrong" same
> type).
>
> A proper fix would be to transition this type as seen from the frontend to
> GIMPLE, for example in a similar way we do for MEM_REFs by piggy-backing
> that on an extra argument, a constant zero pointer of the alias
> pointer type to use
> (which would also serve as a type indicator of the store itself). I'd use a
> target specific internal function for this (not sure if we can have those
> target
> specific, but I guess if it's folded away then that's fine) and get away with
> the overload set.
OK. Will, for now, let's again use the (void *) solution for the time being,
and
add commentary recording this improvement for future work. Same would
go for the vec_vsx_ld/st variations once you get to those.
Otherwise the patch looks ok to me. I'll defer to Segher for approval, of
course.
Thanks,
Bill
>
> Richard.
>
>> The resulting code is verified by testcases powerpc/fold-vec-st-*.c, which
>> has been posted separately.
>>
>> regtest looks clean on power6 and newer.
>>
>> pending feedback, OK for trunk?
>>
>> Thanks,
>> -Will
>>
>> [gcc]
>>
>> 2017-09-21 Will Schmidt <will_schm...@vnet.ibm.com>
>>
>> * config/rs6000/rs6000.c (rs6000_gimple_fold_builtin): Add handling
>> for early folding of vector stores (ALTIVEC_BUILTIN_ST_*).
>> (rs6000_builtin_valid_without_lhs): helper function.
>> * config/rs6000/rs6000-c.c (altivec_resolve_overloaded_builtin):
>> Remove obsoleted code for handling ALTIVEC_BUILTIN_VEC_ST.
>>
>> diff --git a/gcc/config/rs6000/rs6000-c.c b/gcc/config/rs6000/rs6000-c.c
>> index a49db97..4a363a1 100644
>> --- a/gcc/config/rs6000/rs6000-c.c
>> +++ b/gcc/config/rs6000/rs6000-c.c
>> @@ -6470,82 +6470,10 @@ 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_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_ST
>> - && (BYTES_BIG_ENDIAN || !VECTOR_ELT_ORDER_BIG)
>> - && nargs == 3)
>> - {
>> - tree arg0 = (*arglist)[0];
>> - tree arg1 = (*arglist)[1];
>> - tree arg2 = (*arglist)[2];
>> -
>> - /* Construct the masked address. Let existing error handling take
>> - over if we don't have a constant offset. */
>> - arg1 = fold (arg1);
>> -
>> - if (TREE_CODE (arg1) == INTEGER_CST)
>> - {
>> - if (!ptrofftype_p (TREE_TYPE (arg1)))
>> - arg1 = build1 (NOP_EXPR, sizetype, arg1);
>> -
>> - tree arg2_type = TREE_TYPE (arg2);
>> - if (TREE_CODE (arg2_type) == ARRAY_TYPE && c_dialect_cxx ())
>> - {
>> - /* Force array-to-pointer decay for C++. */
>> - arg2 = default_conversion (arg2);
>> - arg2_type = TREE_TYPE (arg2);
>> - }
>> -
>> - /* Find the built-in to make sure a compatible one exists; if not
>> - we fall back to default handling to get the error message. */
>> - 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)
>> - && rs6000_builtin_type_compatible (TREE_TYPE (arg2),
>> - desc->op3))
>> - {
>> - tree addr = fold_build2_loc (loc, POINTER_PLUS_EXPR,
>> arg2_type,
>> - arg2, arg1);
>> - tree aligned
>> - = fold_build2_loc (loc, BIT_AND_EXPR, arg2_type,
>> - addr, build_int_cst (arg2_type, -16));
>> -
>> - tree arg0_type = TREE_TYPE (arg0);
>> - if (TYPE_MODE (arg0_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 address type
>> - to be a may-alias type to avoid this. */
>> - arg0_type
>> - = build_pointer_type_for_mode (arg0_type, Pmode,
>> - true/*can_alias_all*/);
>> - else
>> - arg0_type = build_pointer_type (arg0_type);
>> - aligned = build1 (NOP_EXPR, arg0_type, aligned);
>> - tree stg = build_indirect_ref (loc, aligned, RO_NULL);
>> - tree retval = build2 (MODIFY_EXPR, TREE_TYPE (stg), stg,
>> - convert (TREE_TYPE (stg), arg0));
>> - return retval;
>> - }
>> - }
>> - }
>> -
>> for (n = 0;
>> !VOID_TYPE_P (TREE_VALUE (fnargs)) && n < nargs;
>> fnargs = TREE_CHAIN (fnargs), n++)
>> {
>> tree decl_type = TREE_VALUE (fnargs);
>> diff --git a/gcc/config/rs6000/rs6000.c b/gcc/config/rs6000/rs6000.c
>> index 1978634..ef41534 100644
>> --- a/gcc/config/rs6000/rs6000.c
>> +++ b/gcc/config/rs6000/rs6000.c
>> @@ -16155,10 +16155,29 @@ rs6000_fold_builtin (tree fndecl, int n_args
>> ATTRIBUTE_UNUSED,
>> #else
>> return NULL_TREE;
>> #endif
>> }
>>
>> +/* Helper function to sort out which built-ins may be valid without having
>> + a LHS. */
>> +bool
>> +rs6000_builtin_valid_without_lhs (enum rs6000_builtins fn_code)
>> +{
>> + switch (fn_code)
>> + {
>> + case ALTIVEC_BUILTIN_STVX_V16QI:
>> + case ALTIVEC_BUILTIN_STVX_V8HI:
>> + case ALTIVEC_BUILTIN_STVX_V4SI:
>> + case ALTIVEC_BUILTIN_STVX_V4SF:
>> + case ALTIVEC_BUILTIN_STVX_V2DI:
>> + case ALTIVEC_BUILTIN_STVX_V2DF:
>> + return true;
>> + default:
>> + return false;
>> + }
>> +}
>> +
>> /* Fold a machine-dependent built-in in GIMPLE. (For folding into
>> a constant, use rs6000_fold_builtin.) */
>>
>> bool
>> rs6000_gimple_fold_builtin (gimple_stmt_iterator *gsi)
>> @@ -16182,12 +16201,13 @@ rs6000_gimple_fold_builtin (gimple_stmt_iterator
>> *gsi)
>> fn_code, fn_name1, fn_name2);
>>
>> if (!rs6000_fold_gimple)
>> return false;
>>
>> - /* Generic solution to prevent gimple folding of code without a LHS. */
>> - if (!gimple_call_lhs (stmt))
>> + /* Prevent gimple folding for code that does not have a LHS, unless it is
>> + allowed per the rs6000_builtin_valid_without_lhs helper function. */
>> + if (!gimple_call_lhs (stmt) && !rs6000_builtin_valid_without_lhs
>> (fn_code))
>> return false;
>>
>> switch (fn_code)
>> {
>> /* Flavors of vec_add. We deliberately don't expand
>> @@ -16585,11 +16605,48 @@ rs6000_gimple_fold_builtin (gimple_stmt_iterator
>> *gsi)
>> build_int_cst (arg1_type,
>> 0)));
>> gimple_set_location (g, loc);
>> gsi_replace (gsi, g, true);
>> return true;
>> }
>> -
>> + /* Vector stores. */
>> + case ALTIVEC_BUILTIN_STVX_V16QI:
>> + case ALTIVEC_BUILTIN_STVX_V8HI:
>> + case ALTIVEC_BUILTIN_STVX_V4SI:
>> + case ALTIVEC_BUILTIN_STVX_V4SF:
>> + case ALTIVEC_BUILTIN_STVX_V2DI:
>> + case ALTIVEC_BUILTIN_STVX_V2DF:
>> + {
>> + /* Do not fold for -maltivec=be on LE targets. */
>> + if (VECTOR_ELT_ORDER_BIG && !BYTES_BIG_ENDIAN)
>> + return false;
>> + arg0 = gimple_call_arg (stmt, 0); /* Value to be stored. */
>> + arg1 = gimple_call_arg (stmt, 1); /* Offset. */
>> + tree arg2 = gimple_call_arg (stmt, 2); /* Store-to address. */
>> + location_t loc = gimple_location (stmt);
>> + tree arg0_type = TREE_TYPE (arg0);
>> + tree arg2_type = TREE_TYPE (arg2);
>> + /* 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 arg2. */
>> + gimple_seq stmts = NULL;
>> + tree temp_offset = gimple_convert (&stmts, loc, sizetype, arg1);
>> + tree temp_addr = gimple_build (&stmts, loc, POINTER_PLUS_EXPR,
>> + arg2_type, arg2, temp_offset);
>> + /* Mask off any lower bits from the address. */
>> + tree aligned_addr = gimple_build (&stmts, loc, BIT_AND_EXPR,
>> + arg2_type, temp_addr,
>> + build_int_cst (arg2_type, -16));
>> + gsi_insert_seq_before (gsi, stmts, GSI_SAME_STMT);
>> + /* The desired gimple result should be similar to:
>> + MEM[(__vector floatD.1407 *)_1] = vf1D.2697; */
>> + gimple *g;
>> + g = gimple_build_assign (build2 (MEM_REF, arg0_type, aligned_addr,
>> + build_int_cst (arg2_type, 0)),
>> arg0);
>> + 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;
