[PATCH] x86: optimize stack pointer access (reduce register usage)

Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

arch/i386/kernel/irq.c

@@ -87,7 +87,7 @@ fastcall unsigned int do_IRQ(struct pt_regs *regs)
 		/* build the stack frame on the IRQ stack */
 		isp = (u32*) ((char*)irqctx + sizeof(*irqctx));
 		irqctx->tinfo.task = curctx->tinfo.task;
-		irqctx->tinfo.previous_esp = current_stack_pointer();
+		irqctx->tinfo.previous_esp = current_stack_pointer;
 
 		asm volatile(
 			"       xchgl   %%ebx,%%esp      \n"
@@ -168,7 +168,7 @@ asmlinkage void do_softirq(void)
 		curctx = current_thread_info();
 		irqctx = softirq_ctx[smp_processor_id()];
 		irqctx->tinfo.task = curctx->task;
-		irqctx->tinfo.previous_esp = current_stack_pointer();
+		irqctx->tinfo.previous_esp = current_stack_pointer;
 
 		/* build the stack frame on the softirq stack */
 		isp = (u32*) ((char*)irqctx + sizeof(*irqctx));

include/asm-i386/thread_info.h

@@ -92,12 +92,7 @@ static inline struct thread_info *current_thread_info(void)
 }
 
 /* how to get the current stack pointer from C */
-static inline unsigned long current_stack_pointer(void)
-{
-	unsigned long ti;
-	__asm__("movl %%esp,%0; ":"=r" (ti) : );
-	return ti;
-}
+register unsigned long current_stack_pointer asm("esp");
 
 /* thread information allocation */
 #ifdef CONFIG_DEBUG_STACK_USAGE