On Wed, Jun 14, 2017 at 4:55 PM, Will Schmidt <will_schm...@vnet.ibm.com> wrote:
> On Tue, 2017-06-13 at 10:03 +0200, Richard Biener wrote:
>> On Mon, Jun 12, 2017 at 11:56 PM, Will Schmidt
>> <will_schm...@vnet.ibm.com> wrote:
>> > Hi,
>> >
>> >
>> > diff --git a/gcc/config/rs6000/rs6000.c b/gcc/config/rs6000/rs6000.c
>> > index 63ca2d1..55592fb 100644
>> > --- a/gcc/config/rs6000/rs6000.c
>> > +++ b/gcc/config/rs6000/rs6000.c
>> > @@ -16588,6 +16588,83 @@ rs6000_gimple_fold_builtin (gimple_stmt_iterator
>> > *gsi)
>> > gsi_replace (gsi, g, true);
>> > return true;
>> > }
> <snip>
>> > + /* Flavors of vector shift right. */
>> > + case ALTIVEC_BUILTIN_VSRB:
>> > + case ALTIVEC_BUILTIN_VSRH:
>> > + case ALTIVEC_BUILTIN_VSRW:
>> > + case P8V_BUILTIN_VSRD:
>> > + {
>> > + arg0 = gimple_call_arg (stmt, 0);
>> > + arg1 = gimple_call_arg (stmt, 1);
>> > + lhs = gimple_call_lhs (stmt);
>> > + gimple *g;
>> > + /* convert arg0 to unsigned. */
>> > + arg0 = convert (unsigned_type_for (TREE_TYPE (arg0)), arg0);
>>
>> Please do not use 'convert', instead do ...
>
> Hi Richard,
>
> V3 of this patch , using the gimple_build() convenience helper function
> has been posted, and is the direction I'm going for with this patch. I
> wanted to make sure I fully understood the other options though, so I
> have a question/clarification on the other suggestions:
>
>> > + tree arg0_uns = create_tmp_reg_or_ssa_name
>> > + (unsigned_type_for (TREE_TYPE (arg0)));
>> > + g = gimple_build_assign (arg0_uns, arg0);
>>
>> g = gimple_build_assign (arg0_uns, VIEW_CONVERT_EXPR, usigned_type, arg0);
>
> I tried a few trivial variations of this:
> g = gimple_build_assign (arg0_uns, VIEW_CONVERT_EXPR,
> unsigned_type_for (TREE_TYPE(arg0_uns)), arg0);
>
> which lookd good, but it asserts in gimple_build_assign_1(), on the
> check
> "if (op2)
> {
> gcc_assert (num_ops > 2);
> ...
>
> Trolling around the other code for references, i found and tried this,
> which uses the build1() helper, and appears to work. Is this the gist
> of what you suggested, or would there be another alternative?
>
> g = gimple_build_assign (arg0_uns,
> build1(VIEW_CONVERT_EXPR,
> unsigned_type_for (TREE_TYPE(arg0_uns)), arg0));
>
> Thanks for the feedback, etc. :-)
Yeah, sorry -- the gimple_build machinery handles this GIMPLE wart
transparently but gimple_build_assign does not ...
Richard.
> -Will
>
>
>> You also want to avoid spitting out useless copies here if the
>> arg/result is already unsigned,
>> like via
>>
>> tree arg0_uns = arg0;
>> if (! TYPE_UNSIGNED (TREE_TYPE (arg0_uns)))
>> {
>> ...
>> }
>>
>> > + gimple_set_location (g, gimple_location (stmt));
>> > + gsi_insert_before (gsi, g, GSI_SAME_STMT);
>> > + /* convert lhs to unsigned and do the shift. */
>>
>> Just use lhs if it has the same sign as arg0_uns.
>>
>> > + tree lhs_uns = create_tmp_reg_or_ssa_name
>> > + (unsigned_type_for (TREE_TYPE (lhs)));
>>
>> You can re-use the type of arg0_uns here.
>>
>> > + g = gimple_build_assign (lhs_uns, RSHIFT_EXPR, arg0_uns, arg1);
>> > + gimple_set_location (g, gimple_location (stmt));
>> > + gsi_insert_before (gsi, g, GSI_SAME_STMT);
>> > + /* convert lhs back to a signed type for the return. */
>> > + lhs_uns = convert (signed_type_for (TREE_TYPE (lhs)),lhs_uns);
>> > + g = gimple_build_assign (lhs, lhs_uns);
>>
>> See above for how to perform the conversion.
>>
>> Note that you could use the gimple_build convenience to shorten the code
>> sequence above to
>>
>> gimple_seq stmts = NULL;
>> tree arg0_unsigned = gimple_build (&stmts, VIEW_CONVERT_EXPR,
>>
>> unsigned_type_for (...), arg0);
>> tree res = gimple_build (&stmts, RSHIFT_EXPR, TREE_TYPE (arg0_uns),
>> arg0_uns, arg1);
>> 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);
>>
>> The above gimple_build sequence will fold all the stmts thus remove
>> useless conversions and apply constant folding, etc.
>>
>> Richard.
>>
>> > + gimple_set_location (g, gimple_location (stmt));
>> > + gsi_replace (gsi, g, true);
>> > + return true;
>> > + }
>> > default:
>> > break;
>> > }
>
>
>
