[IA64] speed up syscall path a bit more

Recently I noticed that clearing ar.ssd/ar.csd right before srlz.d is
causing significant stalling in the syscall path.  The patch below
fixes that by moving the register-writes after srlz.d.  On a Madison,
this drops break-based getpid() from 241 to 226 cycles (-15 cycles).
Signed-off-by: NDavid Mosberger-Tang <davidm@hpl.hp.com>
Signed-off-by: NTony Luck <tony.luck@intel.com>

arch/ia64/kernel/entry.S

@@ -728,12 +728,8 @@ ENTRY(ia64_leave_syscall)
 	mov f8=f0		// clear f8
 	;;
 	ld8 r30=[r2],16		// M0|1 load cr.ifs
-	mov.m ar.ssd=r0		// M2 clear ar.ssd
-	cmp.eq p9,p0=r0,r0	// set p9 to indicate that we should restore cr.ifs
-	;;
 	ld8 r25=[r3],16		// M0|1 load ar.unat
-	mov.m ar.csd=r0		// M2 clear ar.csd
-	mov r22=r0		// clear r22
+	cmp.eq p9,p0=r0,r0	// set p9 to indicate that we should restore cr.ifs
 	;;
 	ld8 r26=[r2],PT(B0)-PT(AR_PFS)	// M0|1 load ar.pfs
 (pKStk)	mov r22=psr		// M2 read PSR now that interrupts are disabled
@@ -756,11 +752,15 @@ ENTRY(ia64_leave_syscall)
 	mov f7=f0		// clear f7
 	;;
 	ld8.fill r12=[r2]	// restore r12 (sp)
+	mov.m ar.ssd=r0		// M2 clear ar.ssd
+	mov r22=r0		// clear r22
+
 	ld8.fill r15=[r3]	// restore r15
+(pUStk) st1 [r14]=r17
 	addl r3=THIS_CPU(ia64_phys_stacked_size_p8),r0
 	;;
 (pUStk)	ld4 r3=[r3]		// r3 = cpu_data->phys_stacked_size_p8
-(pUStk) st1 [r14]=r17
+	mov.m ar.csd=r0		// M2 clear ar.csd
 	mov b6=r18		// I0  restore b6
 	;;
 	mov r14=r0		// clear r14