x86: Add defines / utilities for making ISA specific x86 builds

1. Factor out some of the ISA level defines in isa-level.c to
   standalone header isa-level.h

2. Add new headers with ISA level dependent macros for handling
   ifuncs.

Note, this file does not change any code.

Tested with and without multiarch on x86_64 for ISA levels:
{generic, x86-64-v2, x86-64-v3, x86-64-v4}

And m32 with and without multiarch.

1 files changed, 102 insertions, 0 deletions

diff --git a/sysdeps/x86/isa-level.h b/sysdeps/x86/isa-level.h
new file mode 100644
index 0000000000..7cae11c228
--- /dev/null
+++ b/sysdeps/x86/isa-level.h
@@ -0,0 +1,102 @@
+/* Header defining the minimum x86 ISA level
+   Copyright (C) 2022 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   In addition to the permissions in the GNU Lesser General Public
+   License, the Free Software Foundation gives you unlimited
+   permission to link the compiled version of this file with other
+   programs, and to distribute those programs without any restriction
+   coming from the use of this file.  (The Lesser General Public
+   License restrictions do apply in other respects; for example, they
+   cover modification of the file, and distribution when not linked
+   into another program.)
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#ifndef _ISA_LEVEL_H
+#define _ISA_LEVEL_H
+
+#if defined __SSE__ && defined __SSE2__
+/* NB: ISAs, excluding MMX, in x86-64 ISA level baseline are used.  */
+# define __X86_ISA_V1 1
+#else
+# define __X86_ISA_V1 0
+#endif
+
+#if __X86_ISA_V1 && defined __GCC_HAVE_SYNC_COMPARE_AND_SWAP_16               \
+    && defined HAVE_X86_LAHF_SAHF && defined __POPCNT__ && defined __SSE3__   \
+    && defined __SSSE3__ && defined __SSE4_1__ && defined __SSE4_2__
+/* NB: ISAs in x86-64 ISA level v2 are used.  */
+# define __X86_ISA_V2 1
+#else
+# define __X86_ISA_V2 0
+#endif
+
+#if __X86_ISA_V2 && defined __AVX__ && defined __AVX2__ && defined __F16C__   \
+    && defined __FMA__ && defined __LZCNT__ && defined HAVE_X86_MOVBE         \
+    && defined __BMI__ && defined __BMI2__
+/* NB: ISAs in x86-64 ISA level v3 are used.  */
+# define __X86_ISA_V3 1
+#else
+# define __X86_ISA_V3 0
+#endif
+
+#if __X86_ISA_V3 && defined __AVX512F__ && defined __AVX512BW__               \
+    && defined __AVX512CD__ && defined __AVX512DQ__ && defined __AVX512VL__
+/* NB: ISAs in x86-64 ISA level v4 are used.  */
+# define __X86_ISA_V4 1
+#else
+# define __X86_ISA_V4 0
+#endif
+
+#define MINIMUM_X86_ISA_LEVEL                                                 \
+  (__X86_ISA_V1 + __X86_ISA_V2 + __X86_ISA_V3 + __X86_ISA_V4)
+
+
+/*
+ * CPU Features that are hard coded as enabled depending on ISA build
+ *   level.
+ *    - Values > 0 features are always ENABLED if:
+ *          Value >= MINIMUM_X86_ISA_LEVEL
+ */
+
+
+/* ISA level >= 4 guaranteed includes.  */
+#define AVX512VL_X86_ISA_LEVEL 4
+#define AVX512BW_X86_ISA_LEVEL 4
+
+/* ISA level >= 3 guaranteed includes.  */
+#define AVX2_X86_ISA_LEVEL 3
+#define BMI2_X86_ISA_LEVEL 3
+
+/*
+ * NB: This may not be fully assumable for ISA level >= 3. From
+ * looking over the architectures supported in cpu-features.h the
+ * following CPUs may have an issue with this being default set:
+ *      - AMD Excavator
+ */
+#define AVX_Fast_Unaligned_Load_X86_ISA_LEVEL 3
+
+/*
+ * KNL (the only cpu that sets this supported in cpu-features.h)
+ * builds with ISA V1 so this shouldn't harm any architectures.
+ */
+#define Prefer_No_VZEROUPPER_X86_ISA_LEVEL 3
+
+#define ISA_SHOULD_BUILD(isa_build_level)                              \
+  (MINIMUM_X86_ISA_LEVEL <= (isa_build_level) && IS_IN (libc))         \
+   || defined ISA_DEFAULT_IMPL
+
+#endif