[Headers] [MS] Add intrin0.h

[azharudd]

Summary

xatomic.h header in VS 2017 includes <intrin0.h> instead of <intrin.h> like
before. Adding an intrin0.h header which internally includes <intrin.h> when
compiling for the Windows platform.

[rnk]

This sounds like it would defeat what I'm assuming is the intended purpose of intrin0.h, which is to reduce compile time. intrin.h is kind of enormous, and the compile time problems are well-documented. We should investigate what's up with intrin0.h and implement as many builtins as we need to support it.

[azharudd]

In D53912#1281584, @rnk wrote:

This sounds like it would defeat what I'm assuming is the intended purpose of intrin0.h, which is to reduce compile time. intrin.h is kind of enormous, and the compile time problems are well-documented. We should investigate what's up with intrin0.h and implement as many builtins as we need to support it.

I agree. This currently resolves issues with building for ARM64 target using Visual Studio 2017. The missing intrinsics it complains about are already present in intrin.h. We could add those to intrin0.h too but that would duplicate. Please let me know what you think.

[rnk]

In D53912#1284804, @azharudd wrote:

I agree. This currently resolves issues with building for ARM64 target using Visual Studio 2017. The missing intrinsics it complains about are already present in intrin.h. We could add those to intrin0.h too but that would duplicate. Please let me know what you think.

I see that more intrinsics are being added as builtins in D54046. I think that's a good future direction. We should do our best not to add new headers to shadow CRT and SDK headers anymore. +@STL_MSFT

[STL_MSFT]

Yes, the "real builtin" approach seems to be best. For a recent example, D49606 added __shiftright128 as an inline function in intrin.h, but that didn't work with MSVC's STL when I moved our declaration of __shiftright128 from intrin.h to intrin0.h. This was fixed by D50907 making __shiftright128 a real builtin.

For the record, MSVC's intrin.h declares ~880 intrinsics (plus many many more from immintrin.h etc.) and it includes intrin0.h to get the declarations of ~130 intrinsics. There is no duplication - each intrinsic is declared in either the small intrin0.h or the large intrin.h. MSVC's STL then includes intrin0.h in its headers for increased throughput. We occasionally move intrinsics from intrin.h to intrin0.h as we discover that they're needed in the STL (as we've recently done for __shiftright128, _umul128, _BitScanForward[64], and _BitScanReverse[64]).

lib/Headers/CMakeLists.txt

set(files
   fmaintrin.h
   fxsrintrin.h
   gfniintrin.h
   htmintrin.h
   htmxlintrin.h
   ia32intrin.h
   immintrin.h
   intrin.h
+  intrin0.h
   inttypes.h
   invpcidintrin.h
   iso646.h
   limits.h
   lwpintrin.h
   lzcntintrin.h
   mm3dnow.h
   mmintrin.h

lib/Headers/intrin0.h

+/* ===-------- intrin0.h --------------------------------------------------===
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ *
+ *===-----------------------------------------------------------------------===
+ */
+
+/* xatomic.h in VS 2017 includes <intrin0.h> instead of <intrin.h>.
+ * If compiling for the Windows platform, we'll internally just include
+ * <intrin.h>. */
+
+#ifdef _MSC_VER
+#include <intrin.h>
+#endif /* _MSC_VER */