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From: Richard Henderson <rth@twiddle.net>
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Date: Mon, 19 Jun 2017 16:44:38 -0700
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Subject: Re: [Qemu-devel] [PATCH] target/s390x: Implement CSST
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To: Thomas Huth <thuth@redhat.com>, qemu-devel@nongnu.org
Cc: aurelien@aurel32.net, David Hildenbrand <david@redhat.com>

On 06/19/2017 01:08 AM, Thomas Huth wrote:
>> +    /* Sanity check the function code and storage characteristic.  */
>> +    if (fc > 1 || sc > 3) {
>> +        if (!s390_has_feat(S390_FEAT_COMPARE_AND_SWAP_AND_STORE_2)) {
>> +            goto spec_exception;
>> +        }
>> +        if (fc > 2 || sc > 4 || (fc == 2 && (r3 & 1))) {
> 
> I think you could omit the "fc == 2" here. fc has to be bigger than 1
> due to the outer if-statement, and if it is not 2, the first "fc > 1"
> has already triggered. So "fc" has to be 2 here and the "fc == 2" is a
> redundant check.

Not so.  We can also get here with fc == 0 && sc == 4.


r~