x86: atomic64 assembly improvements

In the "xchg" implementation, %ebx and %ecx don't need to be copied
into %eax and %edx respectively (this is only necessary when desiring
to only read the stored value).

In the "add_unless" implementation, swapping the use of %ecx and %esi
for passing arguments allows %esi to become an input only (i.e.
permitting the register to be re-used to address the same object
without reload).

In "{add,sub}_return", doing the initial read64 through the passed in
%ecx decreases a register dependency.

In "inc_not_zero", a branch can be eliminated by or-ing together the
two halves of the current (64-bit) value, and code size can be further
reduced by adjusting the arithmetic slightly.

v2: Undo the folding of "xchg" and "set".

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Link: http://lkml.kernel.org/r/4F19A2BC020000780006E0DC@nat28.tlf.novell.com
Cc: Luca Barbieri <luca@luca-barbieri.com>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

2 files changed, 14 insertions, 21 deletions

diff --git a/arch/x86/lib/atomic64_386_32.S b/arch/x86/lib/atomic64_386_32.S
index e8e7e0d06f42..00933d5e992f 100644
--- a/arch/x86/lib/atomic64_386_32.S
+++ b/arch/x86/lib/atomic64_386_32.S
@@ -137,13 +137,13 @@ BEGIN(dec_return)
 RET_ENDP
 #undef v
 
-#define v %ecx
+#define v %esi
 BEGIN(add_unless)
-        addl %eax, %esi
+        addl %eax, %ecx
         adcl %edx, %edi
         addl  (v), %eax
         adcl 4(v), %edx
-        cmpl %eax, %esi
+        cmpl %eax, %ecx
         je 3f
 1:
         movl %eax,  (v)
diff --git a/arch/x86/lib/atomic64_cx8_32.S b/arch/x86/lib/atomic64_cx8_32.S
index 391a083674b4..f5cc9eb1d51b 100644
--- a/arch/x86/lib/atomic64_cx8_32.S
+++ b/arch/x86/lib/atomic64_cx8_32.S
@@ -55,8 +55,6 @@ ENDPROC(atomic64_set_cx8)
 ENTRY(atomic64_xchg_cx8)
         CFI_STARTPROC
 
-        movl %ebx, %eax
-        movl %ecx, %edx
 1:
         LOCK_PREFIX
         cmpxchg8b (%esi)
@@ -78,7 +76,7 @@ ENTRY(atomic64_\func\()_return_cx8)
         movl %edx, %edi
         movl %ecx, %ebp
 
-        read64 %ebp
+        read64 %ecx
 1:
         movl %eax, %ebx
         movl %edx, %ecx
@@ -159,23 +157,22 @@ ENTRY(atomic64_add_unless_cx8)
         SAVE ebx
 /* these just push these two parameters on the stack */
         SAVE edi
-        SAVE esi
+        SAVE ecx
 
-        movl %ecx, %ebp
-        movl %eax, %esi
+        movl %eax, %ebp
         movl %edx, %edi
 
-        read64 %ebp
+        read64 %esi
 1:
         cmpl %eax, 0(%esp)
         je 4f
 2:
         movl %eax, %ebx
         movl %edx, %ecx
-        addl %esi, %ebx
+        addl %ebp, %ebx
         adcl %edi, %ecx
         LOCK_PREFIX
-        cmpxchg8b (%ebp)
+        cmpxchg8b (%esi)
         jne 1b
 
         movl $1, %eax
@@ -199,13 +196,13 @@ ENTRY(atomic64_inc_not_zero_cx8)
 
         read64 %esi
 1:
-        testl %eax, %eax
-        je 4f
-2:
+        movl %eax, %ecx
+        orl %edx, %ecx
+        jz 3f
         movl %eax, %ebx
-        movl %edx, %ecx
+        xorl %ecx, %ecx
         addl $1, %ebx
-        adcl $0, %ecx
+        adcl %edx, %ecx
         LOCK_PREFIX
         cmpxchg8b (%esi)
         jne 1b
@@ -214,9 +211,5 @@ ENTRY(atomic64_inc_not_zero_cx8)
 3:
         RESTORE ebx
         ret
-4:
-        testl %edx, %edx
-        jne 2b
-        jmp 3b
         CFI_ENDPROC
 ENDPROC(atomic64_inc_not_zero_cx8)