Optimize x86-64 sem_wait for uncontested semaphore.

diff --git a/nptl/ChangeLog b/nptl/ChangeLog
index 5204ad1..5db47a1 100644 (file)
--- a/nptl/ChangeLog
+++ b/nptl/ChangeLog
@@ -1,5 +1,8 @@
 2009-07-17  Ulrich Drepper  <drepper@redhat.com>
 
+       * sysdeps/unix/sysv/linux/x86_64/sem_wait.S (sem_wait): Optimize
+       handling of uncontested semaphore.
+
        * sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S
        (__condvar_cleanup): Rewrite to use cfi directives instead of
        hand-coded unwind tables.

diff --git a/nptl/sysdeps/unix/sysv/linux/x86_64/sem_wait.S b/nptl/sysdeps/unix/sysv/linux/x86_64/sem_wait.S
index de6a53b..a01d745 100644 (file)
--- a/nptl/sysdeps/unix/sysv/linux/x86_64/sem_wait.S
+++ b/nptl/sysdeps/unix/sysv/linux/x86_64/sem_wait.S
@@ -40,18 +40,11 @@ sem_wait:
        cfi_personality(DW_EH_PE_udata4, __gcc_personality_v0)
        cfi_lsda(DW_EH_PE_udata4, .LexceptSTART)
 #endif
-       pushq   %r12
-       cfi_adjust_cfa_offset(8)
-       cfi_rel_offset(%r12, 0)
-       pushq   %r13
-       cfi_adjust_cfa_offset(8)
-       cfi_rel_offset(%r13, 0)
-       movq    %rdi, %r13
 
 #if VALUE == 0
-       movl    (%r13), %eax
+       movl    (%rdi), %eax
 #else
-       movl    VALUE(%r13), %eax
+       movl    VALUE(%rdi), %eax
 #endif
 2:     testl   %eax, %eax
        je      1f
@@ -59,27 +52,24 @@ sem_wait:
        leal    -1(%rax), %edx
        LOCK
 #if VALUE == 0
-       cmpxchgl %edx, (%r13)
+       cmpxchgl %edx, (%rdi)
 #else
-       cmpxchgl %edx, VALUE(%r13)
+       cmpxchgl %edx, VALUE(%rdi)
 #endif
        jne     2b
 
-7:     xorl    %eax, %eax
-
-9:     popq    %r13
-       cfi_adjust_cfa_offset(-8)
-       cfi_restore(%r13)
-       popq    %r12
-       cfi_adjust_cfa_offset(-8)
-       cfi_restore(%r12)
-
+       xorl    %eax, %eax
        retq
 
-       cfi_adjust_cfa_offset(2 * 8)
-       cfi_rel_offset(%r12, 8)
+1:     pushq   %r12
+       cfi_adjust_cfa_offset(8)
+       cfi_rel_offset(%r12, 0)
+       pushq   %r13
+       cfi_adjust_cfa_offset(8)
        cfi_rel_offset(%r13, 0)
-1:     LOCK
+       movq    %rdi, %r13
+
+       LOCK
        addq    $1, NWAITERS(%r13)
 
 .LcleanupSTART:
@@ -128,8 +118,21 @@ sem_wait:
 
        LOCK
        subq    $1, NWAITERS(%r13)
-       jmp     7b
 
+       xorl    %eax, %eax
+
+9:     popq    %r13
+       cfi_adjust_cfa_offset(-8)
+       cfi_restore(%r13)
+       popq    %r12
+       cfi_adjust_cfa_offset(-8)
+       cfi_restore(%r12)
+
+       retq
+
+       cfi_adjust_cfa_offset(2 * 8)
+       cfi_rel_offset(%r12, 8)
+       cfi_rel_offset(%r13, 0)
 4:     negq    %r12
 #if USE___THREAD
        movq    errno@gottpoff(%rip), %rdx