target/arm: Add cpu local variable to exception_return helper

We already call env_archcpu() multiple times within the
exception_return helper function, and we're about to want to
add another use of the ARMCPU pointer. Add a local variable
cpu so we can call env_archcpu() just once.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>

target/arm/tcg/helper-a64.c

@@ -631,6 +631,7 @@ static void cpsr_write_from_spsr_elx(CPUARMState *env,
 
 void HELPER(exception_return)(CPUARMState *env, uint64_t new_pc)
 {
+    ARMCPU *cpu = env_archcpu(env);
     int cur_el = arm_current_el(env);
     unsigned int spsr_idx = aarch64_banked_spsr_index(cur_el);
     uint32_t spsr = env->banked_spsr[spsr_idx];
@@ -682,7 +683,7 @@ void HELPER(exception_return)(CPUARMState *env, uint64_t new_pc)
     }
 
     bql_lock();
-    arm_call_pre_el_change_hook(env_archcpu(env));
+    arm_call_pre_el_change_hook(cpu);
     bql_unlock();
 
     if (!return_to_aa64) {
@@ -710,7 +711,7 @@ void HELPER(exception_return)(CPUARMState *env, uint64_t new_pc)
         int tbii;
 
         env->aarch64 = true;
-        spsr &= aarch64_pstate_valid_mask(&env_archcpu(env)->isar);
+        spsr &= aarch64_pstate_valid_mask(&cpu->isar);
         pstate_write(env, spsr);
         if (!arm_singlestep_active(env)) {
             env->pstate &= ~PSTATE_SS;
@@ -749,7 +750,7 @@ void HELPER(exception_return)(CPUARMState *env, uint64_t new_pc)
     aarch64_sve_change_el(env, cur_el, new_el, return_to_aa64);
 
     bql_lock();
-    arm_call_el_change_hook(env_archcpu(env));
+    arm_call_el_change_hook(cpu);
     bql_unlock();
 
     return;