On Jul 23, 2009, at 9:33 PM, Eli Friedman wrote:
>>> + // See if this is a known constant.
>>> + int KnownVal = TryEvaluateBool(B->getLHS());
>>> + if (KnownVal != -1 && (B->getOpcode() == BinaryOperator::LOr))
>>> + KnownVal = !KnownVal;
>>> +
>>> // Now link the LHSBlock with RHSBlock.
>>> if (B->getOpcode() == BinaryOperator::LOr) {
>>> - if (KnownTrue)
>>> + if (KnownVal == true)
>>> LHSBlock->addSuccessor(0);
>>> else
>>> LHSBlock->addSuccessor(ConfluenceBlock);
>>> - if (KnownFalse)
>>> + if (KnownVal == false)
>>> LHSBlock->addSuccessor(0);
>>
>> Hi Mike,
>>
>> This looks a little suspicious to me. Doesn't '-1' convert to 'true'
>> when an int is casted to a bool? This would cause 'KnowVal == true'
>> to evaluate to true even when 'KnownVal' is -1.
>
> (int)x == false is semantically equivalent to (int)x == 0 due to
> integer promotion rules. That said, it is slightly confusing the way
> it's written.
The problem isn't with 'x == 0', but with 'x == -1'. Since (I
believe) both '1' and '-1' convert to true when int is casted to a
bool, the 'KnownVal == true' would evaluate to true in both cases
(which isn't the desired behavior).
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