[PATCH] i386: Evaluate constant cpu features at runtime

Redefine cpu_has() to evaluate cpu features already checked in early
boot at compile time.  This way the compiler might eliminate some dead code.
Signed-off-by: Andi Kleen <ak@suse.de>

1 files changed, 6 insertions, 2 deletions

diff --git a/include/asm-i386/cpufeature.h b/include/asm-i386/cpufeature.h
index e66d004aa651..20e849ae6ddc 100644
--- a/include/asm-i386/cpufeature.h
+++ b/include/asm-i386/cpufeature.h
@@ -106,8 +106,12 @@
 #define X86_FEATURE_LAHF_LM     (6*32+ 0) /* LAHF/SAHF in long mode */
 #define X86_FEATURE_CMP_LEGACY  (6*32+ 1) /* If yes HyperThreading not valid */
 
-#define cpu_has(c, bit)         test_bit(bit, (c)->x86_capability)
-#define boot_cpu_has(bit)       test_bit(bit, boot_cpu_data.x86_capability)
+#define cpu_has(c, bit)                                 \
+        ((__builtin_constant_p(bit) && (bit) < 32 &&    \
+                (1UL << (bit)) & REQUIRED_MASK1) ?      \
+                1 :                                     \
+        test_bit(bit, (c)->x86_capability))
+#define boot_cpu_has(bit)       cpu_has(&boot_cpu_data, bit)
 
 #define cpu_has_fpu             boot_cpu_has(X86_FEATURE_FPU)
 #define cpu_has_vme             boot_cpu_has(X86_FEATURE_VME)