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<?xml version="1.0" encoding="UTF-8"?> |
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<!-- |
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Copyright (c) 2017 OpenPOWER Foundation |
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Licensed under the Apache License, Version 2.0 (the "License"); |
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you may not use this file except in compliance with the License. |
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You may obtain a copy of the License at |
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http://www.apache.org/licenses/LICENSE-2.0 |
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Unless required by applicable law or agreed to in writing, software |
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distributed under the License is distributed on an "AS IS" BASIS, |
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
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See the License for the specific language governing permissions and |
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limitations under the License. |
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--> |
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<chapter xmlns="http://docbook.org/ns/docbook" |
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xmlns:xi="http://www.w3.org/2001/XInclude" |
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xmlns:xlink="http://www.w3.org/1999/xlink" |
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version="5.0" |
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xml:id="ch_howto_start"> |
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<title>How do we work this?</title> |
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<para>The working assumption is to start with the existing GCC headers from |
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<literal>./gcc/config/i386/</literal>, then convert them to PowerISA |
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and add them to <literal>./gcc/config/rs6000/</literal>. |
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I assume we will replicate the existing header structure |
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and retain the existing header file and intrinsic names. |
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This also allows us to reuse existing DejaGNU test cases from |
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<literal>./gcc/testsuite/gcc.target/i386</literal>, modify |
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them as needed for the POWER target, and add them to |
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<literal>./gcc/testsuite/gcc.target/powerpc</literal>.</para> |
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<para>We can be flexible on the sequence that headers/intrinsics and test |
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cases are ported. This should be based on customer need and resolving |
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internal dependencies. This implies an oldest-to-newest / bottoms-up (MMX, |
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SSE, SSE2, …) strategy. The assumption is, existing community and user |
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application codes, are more likely to have optimized code for previous |
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generation ubiquitous (SSE, SSE2, ...) processors than the latest (and rare) |
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SkyLake AVX512.</para> |
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<para>I would start with an existing header from the current GCC |
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./gcc/config/i386/ and copy the header comment (including FSF copyright) down |
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to any vector typedefs used in the API or implementation. Skip the Intel |
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intrinsic implementation code for now, but add the ending #end if matching the |
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headers conditional guard against multiple inclusion. You can add additional |
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#include's as needed. For example: |
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<programlisting><![CDATA[/* Copyright (C) 2003-2017 Free Software Foundation, Inc |
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... |
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/* This header provides a best effort implementation of the Intel X86 |
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* SSE2 intrinsics for the PowerPC target. This implementation is a |
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* combination of compiled C vector codes or equivalent sequences of |
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* GCC vector builtins from the GCC PowerPC Altivec target. |
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* |
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* However some details of this implementation will differ from |
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* the X86 due to differences in the underlying hardware or GCC |
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* implementation. For example the PowerPC target only uses unordered |
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* floating point compares. */ |
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#ifndef EMMINTRIN_H_ |
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#define EMMINTRIN_H_ |
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#include <altivec.h> |
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#include <assert.h> |
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/* We need definitions from the SSE header files. */ |
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#include <xmmintrin.h> |
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/* The Intel API is flexible enough that we must allow aliasing with other |
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vector types, and their scalar components. */ |
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typedef float __m128 __attribute__ ((__vector_size__ (16), __may_alias__)); |
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/* Internal data types for implementing the intrinsics. */ |
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typedef __vector float __v4sf; |
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/* more typedefs. */ |
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/* The intrinsic implmentations go here. */ |
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#endif /* EMMINTRIN_H_ */]]></programlisting></para> |
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<note><para> |
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The interface typedef (__m128) uses the GCC vector builtin |
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extension syntax, while the internal typedef (__v4sf) uses the altivec |
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vector extension syntax. |
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This allows the internal typedefs to work correctly with the PowerPC |
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overloaded vector builtins. Also we use the __vector (vs vector) type prefix |
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to avoid name space conflicts with C++. |
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</para></note> |
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<para>Then you can start adding small groups of related intrinsic |
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implementations to the header to be compiled and examine the generated code. |
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Once you have what looks like reasonable code you can grep through |
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./gcc/testsuite/gcc.target/i386 for examples using the intrinsic names you |
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just added. You should be able to find functional tests for most X86 |
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intrinsics. </para> |
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<para>The |
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<link xlink:href="https://gcc.gnu.org/onlinedocs/gccint/Testsuites.html#Testsuites"> |
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<emphasis role="italic">GCC testsuite</emphasis></link> |
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uses the DejaGNU test framework as documented in the |
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<link xlink:href="https://gcc.gnu.org/onlinedocs/gccint/"> |
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<emphasis role="italic">GNU Compiler Collection (GCC) |
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Internals</emphasis></link> |
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manual. GCC adds its own DejaGNU directives and extensions, |
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that are embedded in the testsuite source as comments. Some are platform |
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specific and will need to be adjusted for tests that are ported to our |
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platform. For example |
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<programlisting><![CDATA[/* { dg-do run } */ |
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/* { dg-options "-O2 -msse2" } */ |
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/* { dg-require-effective-target sse2 } */]]></programlisting></para> |
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<para>should become something like |
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<programlisting><![CDATA[/* { dg-do run } */ |
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/* { dg-options "-O3 -mpower8-vector" } */ |
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/* { dg-require-effective-target lp64 } */ |
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/* { dg-require-effective-target p8vector_hw { target powerpc*-*-* } } */]]></programlisting></para> |
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<para>Repeat this process until you have equivalent DejaGNU test |
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implementations for all the intrinsics in that header and associated |
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test cases that execute without error.</para> |
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<xi:include href="sec_prefered_methods.xml"/> |
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<xi:include href="sec_prepare.xml"/> |
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<xi:include href="sec_differences.xml"/> |
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</chapter> |
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