ARC: fold __builtin_constant_p() into test_bit()

This makes test_bit() more like its siblings *_bit() routines.
Also add some comments about the constant @nr micro-optimization

Signed-off-by: Vineet Gupta <vgupta@synopsys.com>

1 files changed, 18 insertions, 13 deletions

diff --git a/arch/arc/include/asm/bitops.h b/arch/arc/include/asm/bitops.h
index 1a5bf07eefe2..4051e9525939 100644
--- a/arch/arc/include/asm/bitops.h
+++ b/arch/arc/include/asm/bitops.h
@@ -32,6 +32,20 @@ static inline void set_bit(unsigned long nr, volatile unsigned long *m)
 
         m += nr >> 5;
 
+        /*
+         * ARC ISA micro-optimization:
+         *
+         * Instructions dealing with bitpos only consider lower 5 bits (0-31)
+         * e.g (x << 33) is handled like (x << 1) by ASL instruction
+         *  (mem pointer still needs adjustment to point to next word)
+         *
+         * Hence the masking to clamp @nr arg can be elided in general.
+         *
+         * However if @nr is a constant (above assumed it in a register),
+         * and greater than 31, gcc can optimize away (x << 33) to 0,
+         * as overflow, given the 32-bit ISA. Thus masking needs to be done
+         * for constant @nr, but no code is generated due to const prop.
+         */
         if (__builtin_constant_p(nr))
                 nr &= 0x1f;
 
@@ -374,29 +388,20 @@ __test_and_change_bit(unsigned long nr, volatile unsigned long *m)
  * This routine doesn't need to be atomic.
  */
 static inline int
-__constant_test_bit(unsigned int nr, const volatile unsigned long *addr)
-{
-        return ((1UL << (nr & 31)) &
-                (((const volatile unsigned int *)addr)[nr >> 5])) != 0;
-}
-
-static inline int
-__test_bit(unsigned int nr, const volatile unsigned long *addr)
+test_bit(unsigned int nr, const volatile unsigned long *addr)
 {
         unsigned long mask;
 
         addr += nr >> 5;
 
-        /* ARC700 only considers 5 bits in bit-fiddling insn */
+        if (__builtin_constant_p(nr))
+                nr &= 0x1f;
+
         mask = 1 << nr;
 
         return ((mask & *addr) != 0);
 }
 
-#define test_bit(nr, addr)      (__builtin_constant_p(nr) ? \
-                                        __constant_test_bit((nr), (addr)) : \
-                                        __test_bit((nr), (addr)))
-
 /*
  * Count the number of zeros, starting from MSB
  * Helper for fls( ) friends