[Headers] Fix up some conditionals

[probinson]

Summary

While looking at adding intrinsic function descriptions, I found some
oddities in the conditionals. I've fiddled with some of them. This is
not a complete audit.

Two headers have been changed to require only immintrin.h and not
x86intrin.h; this conforms to which header actually includes them, and with
Intel documentation.

One function in bmi2intrin.h was defined only in 32-bit mode, for no
apparent reason; I fixed that.

clzerointrin.h is included from x86intrin.h, so I made it not check for immintrin.h.
This is an AMD only instruction so there's no Intel documentation to check against.

[craig.topper]

LGTM

[craig.topper]

The mulx function being 32-bit mode only is also true in gcc. It probably won't generate a mulx instruction on x86-64. Maybe that's why it was 32-bit only? But it should still be functionally correct.

[probinson]

The Intel documentation doesn't hint that _mulx_32 isn't available in 64-bit mode. I'm guessing gcc messed up and we copied them.

[probinson]

Committed [[ here | https://github.com/llvm/llvm-project/commit/3db8410487ce704f02ef8a175e87295d4e86c8df ]] and closing manually because I forgot to put the review link in the commit message.

[pengfei]

In D153576#4442096, @craig.topper wrote:

The mulx function being 32-bit mode only is also true in gcc. It probably won't generate a mulx instruction on x86-64. Maybe that's why it was 32-bit only? But it should still be functionally correct.

It's not functionally correct. Candidate fix D153620.

clang/lib/Headers/bmi2intrin.h

 /*===---- bmi2intrin.h - BMI2 intrinsics -----------------------------------===
  *
  * Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
  * See https://llvm.org/LICENSE.txt for license information.
  * SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
  *
  *===-----------------------------------------------------------------------===
  */
 
-#if !defined __X86INTRIN_H && !defined __IMMINTRIN_H
-#error "Never use <bmi2intrin.h> directly; include <x86intrin.h> instead."
+#ifndef __IMMINTRIN_H
+#error "Never use <bmi2intrin.h> directly; include <immintrin.h> instead."
 #endif
 
 #ifndef __BMI2INTRIN_H
 #define __BMI2INTRIN_H
 
 /* Define the default attributes for the functions in this file. */
 #define __DEFAULT_FN_ATTRS __attribute__((__always_inline__, __nodebug__, __target__("bmi2")))
 

 }
 
 static __inline__ unsigned int __DEFAULT_FN_ATTRS
 _pext_u32(unsigned int __X, unsigned int __Y)
 {
   return __builtin_ia32_pext_si(__X, __Y);
 }
 
+static __inline__ unsigned int __DEFAULT_FN_ATTRS
+_mulx_u32(unsigned int __X, unsigned int __Y, unsigned int *__P)
+{
+  unsigned long long __res = (unsigned long long) __X * __Y;
+  *__P = (unsigned int)(__res >> 32);
+  return (unsigned int)__res;
+}
+
 #ifdef  __x86_64__
 
 static __inline__ unsigned long long __DEFAULT_FN_ATTRS
 _bzhi_u64(unsigned long long __X, unsigned long long __Y)
 {
   return __builtin_ia32_bzhi_di(__X, __Y);
 }
 

 _mulx_u64 (unsigned long long __X, unsigned long long __Y,
      unsigned long long *__P)
 {
   unsigned __int128 __res = (unsigned __int128) __X * __Y;
   *__P = (unsigned long long) (__res >> 64);
   return (unsigned long long) __res;
 }
 
-#else /* !__x86_64__ */
-
-static __inline__ unsigned int __DEFAULT_FN_ATTRS
-_mulx_u32 (unsigned int __X, unsigned int __Y, unsigned int *__P)
-{
-  unsigned long long __res = (unsigned long long) __X * __Y;
-  *__P = (unsigned int) (__res >> 32);
-  return (unsigned int) __res;
-}
-
-#endif /* !__x86_64__  */
+#endif /* __x86_64__  */
 
 #undef __DEFAULT_FN_ATTRS
 
 #endif /* __BMI2INTRIN_H */

clang/lib/Headers/clzerointrin.h

 /*===----------------------- clzerointrin.h - CLZERO ----------------------===
  *
  * Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
  * See https://llvm.org/LICENSE.txt for license information.
  * SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
  *
  *===-----------------------------------------------------------------------===
  */
-#if !defined __X86INTRIN_H && !defined __IMMINTRIN_H
+#ifndef __X86INTRIN_H
 #error "Never use <clzerointrin.h> directly; include <x86intrin.h> instead."
 #endif
 
 #ifndef __CLZEROINTRIN_H
 #define __CLZEROINTRIN_H
 
 /* Define the default attributes for the functions in this file. */
 #define __DEFAULT_FN_ATTRS \

clang/lib/Headers/rdseedintrin.h

 /*===---- rdseedintrin.h - RDSEED intrinsics -------------------------------===
  *
  * Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
  * See https://llvm.org/LICENSE.txt for license information.
  * SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
  *
  *===-----------------------------------------------------------------------===
  */
 
-#if !defined __X86INTRIN_H && !defined __IMMINTRIN_H
-#error "Never use <rdseedintrin.h> directly; include <x86intrin.h> instead."
+#ifndef __IMMINTRIN_H
+#error "Never use <rdseedintrin.h> directly; include <immintrin.h> instead."
 #endif
 
 #ifndef __RDSEEDINTRIN_H
 #define __RDSEEDINTRIN_H
 
 /* Define the default attributes for the functions in this file. */
 #define __DEFAULT_FN_ATTRS __attribute__((__always_inline__, __nodebug__, __target__("rdseed")))