x86: Use asm goto to implement better modify_and_test() functions

Linus suggested using asm goto to get rid of the typical SETcc + TEST
instruction pair -- which also clobbers an extra register -- for our
typical modify_and_test() functions.

Because asm goto doesn't allow output fields it has to include an
unconditinal memory clobber when it changes a memory variable to force
a reload.

Luckily all atomic ops already imply a compiler barrier to go along
with their memory barrier semantics.

Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/n/tip-0mtn9siwbeo1d33bap1422se@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 4 insertions, 24 deletions

diff --git a/arch/x86/include/asm/local.h b/arch/x86/include/asm/local.h
index 2d89e3980cbd..5b23e605e707 100644
--- a/arch/x86/include/asm/local.h
+++ b/arch/x86/include/asm/local.h
@@ -52,12 +52,7 @@ static inline void local_sub(long i, local_t *l)
  */
 static inline int local_sub_and_test(long i, local_t *l)
 {
-        unsigned char c;
-
-        asm volatile(_ASM_SUB "%2,%0; sete %1"
-                     : "+m" (l->a.counter), "=qm" (c)
-                     : "ir" (i) : "memory");
-        return c;
+        GEN_BINARY_RMWcc(_ASM_SUB, l->a.counter, i, "%0", "e");
 }
 
 /**
@@ -70,12 +65,7 @@ static inline int local_sub_and_test(long i, local_t *l)
  */
 static inline int local_dec_and_test(local_t *l)
 {
-        unsigned char c;
-
-        asm volatile(_ASM_DEC "%0; sete %1"
-                     : "+m" (l->a.counter), "=qm" (c)
-                     : : "memory");
-        return c != 0;
+        GEN_UNARY_RMWcc(_ASM_DEC, l->a.counter, "%0", "e");
 }
 
 /**
@@ -88,12 +78,7 @@ static inline int local_dec_and_test(local_t *l)
  */
 static inline int local_inc_and_test(local_t *l)
 {
-        unsigned char c;
-
-        asm volatile(_ASM_INC "%0; sete %1"
-                     : "+m" (l->a.counter), "=qm" (c)
-                     : : "memory");
-        return c != 0;
+        GEN_UNARY_RMWcc(_ASM_INC, l->a.counter, "%0", "e");
 }
 
 /**
@@ -107,12 +92,7 @@ static inline int local_inc_and_test(local_t *l)
  */
 static inline int local_add_negative(long i, local_t *l)
 {
-        unsigned char c;
-
-        asm volatile(_ASM_ADD "%2,%0; sets %1"
-                     : "+m" (l->a.counter), "=qm" (c)
-                     : "ir" (i) : "memory");
-        return c;
+        GEN_BINARY_RMWcc(_ASM_ADD, l->a.counter, i, "%0", "s");
 }
 
 /**