Merge tag 'x86_asm_for_v6.1_rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull x86 asm update from Borislav Petkov:

 - Use the __builtin_ffs/ctzl() compiler builtins for the constant
   argument case in the kernel's optimized ffs()/ffz() helpers in order
   to make use of the compiler's constant folding optmization passes.

* tag 'x86_asm_for_v6.1_rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/asm/bitops: Use __builtin_ctzl() to evaluate constant expressions
  x86/asm/bitops: Use __builtin_ffs() to evaluate constant expressions

Author: torvalds

arch/x86/include/asm/bitops.h

@@ -247,17 +247,30 @@ arch_test_bit_acquire(unsigned long nr, const volatile unsigned long *addr)
 					  variable_test_bit(nr, addr);
 }
 
+static __always_inline unsigned long variable__ffs(unsigned long word)
+{
+	asm("rep; bsf %1,%0"
+		: "=r" (word)
+		: "rm" (word));
+	return word;
+}
+
 /**
  * __ffs - find first set bit in word
  * @word: The word to search
  *
  * Undefined if no bit exists, so code should check against 0 first.
  */
-static __always_inline unsigned long __ffs(unsigned long word)
+#define __ffs(word)				\
+	(__builtin_constant_p(word) ?		\
+	 (unsigned long)__builtin_ctzl(word) :	\
+	 variable__ffs(word))
+
+static __always_inline unsigned long variable_ffz(unsigned long word)
 {
 	asm("rep; bsf %1,%0"
 		: "=r" (word)
-		: "rm" (word));
+		: "r" (~word));
 	return word;
 }
 
@@ -267,13 +280,10 @@ static __always_inline unsigned long __ffs(unsigned long word)
  *
  * Undefined if no zero exists, so code should check against ~0UL first.
  */
-static __always_inline unsigned long ffz(unsigned long word)
-{
-	asm("rep; bsf %1,%0"
-		: "=r" (word)
-		: "r" (~word));
-	return word;
-}
+#define ffz(word)				\
+	(__builtin_constant_p(word) ?		\
+	 (unsigned long)__builtin_ctzl(~word) :	\
+	 variable_ffz(word))
 
 /*
  * __fls: find last set bit in word
@@ -292,18 +302,7 @@ static __always_inline unsigned long __fls(unsigned long word)
 #undef ADDR
 
 #ifdef __KERNEL__
-/**
- * ffs - find first set bit in word
- * @x: the word to search
- *
- * This is defined the same way as the libc and compiler builtin ffs
- * routines, therefore differs in spirit from the other bitops.
- *
- * ffs(value) returns 0 if value is 0 or the position of the first
- * set bit if value is nonzero. The first (least significant) bit
- * is at position 1.
- */
-static __always_inline int ffs(int x)
+static __always_inline int variable_ffs(int x)
 {
 	int r;
 
@@ -333,6 +332,19 @@ static __always_inline int ffs(int x)
 	return r + 1;
 }
 
+/**
+ * ffs - find first set bit in word
+ * @x: the word to search
+ *
+ * This is defined the same way as the libc and compiler builtin ffs
+ * routines, therefore differs in spirit from the other bitops.
+ *
+ * ffs(value) returns 0 if value is 0 or the position of the first
+ * set bit if value is nonzero. The first (least significant) bit
+ * is at position 1.
+ */
+#define ffs(x) (__builtin_constant_p(x) ? __builtin_ffs(x) : variable_ffs(x))
+
 /**
  * fls - find last set bit in word
  * @x: the word to search