x86: Add support to build strcmp/strlen/strchr with explicit ISA level

1. Add default ISA level selection in non-multiarch/rtld
   implementations.

2. Add ISA level build guards to different implementations.
    - I.e strcmp-avx2.S which is ISA level 3 will only build if
      compiled ISA level <= 3. Otherwise there is no reason to
      include it as we will always use one of the ISA level 4
      implementations (strcmp-evex.S).

3. Refactor the ifunc selector and ifunc implementation list to use
   the ISA level aware wrapper macros that allow functions below the
   compiled ISA level (with a guranteed replacement) to be skipped.

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, 10 insertions, 0 deletions

diff --git a/sysdeps/x86/isa-level.h b/sysdeps/x86/isa-level.h
index 77f9e2c0c3..3c4480aba7 100644
--- a/sysdeps/x86/isa-level.h
+++ b/sysdeps/x86/isa-level.h
@@ -84,6 +84,7 @@
 
 /* ISA level >= 2 guaranteed includes.  */
 #define SSE4_2_X86_ISA_LEVEL 2
+#define SSE4_1_X86_ISA_LEVEL 2
 #define SSSE3_X86_ISA_LEVEL 2
 
 
@@ -101,9 +102,18 @@
    when ISA level < 3.  */
 #define Prefer_No_VZEROUPPER_X86_ISA_LEVEL 3
 
+/* NB: This feature is disable when ISA level >= 3.  All CPUs with
+   this feature don't run on glibc built with ISA level >= 3.  */
+#define Slow_SSE42_X86_ISA_LEVEL 3
+
 /* Feature(s) enabled when ISA level >= 2.  */
 #define Fast_Unaligned_Load_X86_ISA_LEVEL 2
 
+/* NB: This feature is disable when ISA level >= 2, which was enabled
+   for the early Atom CPUs.  */
+#define Slow_BSF_X86_ISA_LEVEL 2
+
+
 /* Both X86_ISA_CPU_FEATURE_USABLE_P and X86_ISA_CPU_FEATURES_ARCH_P
    macros are wrappers for the respective CPU_FEATURE{S}_{USABLE|ARCH}_P
    runtime checks.  They differ in two ways.