Re: [Qemu-devel] [PATCH v2 2/2] target-arm: Implement MDCR_EL3.TPM and MDCR_EL2.TPM traps

[Peter Maydell <peter.maydell@linaro.org>]

On 19 February 2016 at 19:38, Alistair Francis <alistair23@gmail.com> wrote:
> On Fri, Feb 19, 2016 at 6:39 AM, Peter Maydell <peter.maydell@linaro.org> wrote:
>> +/* Check for traps to performance monitor registers, which are controlled
>> + * by MDCR_EL2.TPM for EL2 and MDCR_EL3.TPM for EL3.
>> + */
>> +static CPAccessResult access_tpm(CPUARMState *env, const ARMCPRegInfo *ri,
>> +                                 bool isread)
>> +{
>> +    int el = arm_current_el(env);
>> +
>> +    if (el < 2 && (env->cp15.mdcr_el2 & MDCR_TPM)
>> +        && !arm_is_secure_below_el3(env)) {
>> +        return CP_ACCESS_TRAP_EL2;
>> +    }
>> +    if (el < 3 && (env->cp15.mdcr_el3 & MDCR_TPM)) {
>> +        return CP_ACCESS_TRAP_EL3;
>> +    }
>
> Hey Peter,
>
> Why not use else if?

I generally tend not to use else-if ladders if the thing
in the conditional returns unconditionally, just as a
personal style preference. "if () { X } else if () { Y } Z"
implies a possible control flow path of "take the if
branch so run X, then skip Y, and continue after to run Z",
and if X returns unconditionally that can't happen.
It also matches up with the usual approach of
   if (something) {
       early return;
   }
   main body of function;

which you wouldn't want to write as
   if (something) {
      early return;
   } else {
      main body;
   }

thanks
-- PMM