[llvm-commits] [llvm] r51268 - in /llvm/trunk: lib/Transforms/Scalar/InstructionCombining.cpp test/Transforms/InstCombine/sitofp.ll

[Chris Lattner]

On May 19, 2008, at 3:47 PM, Neil Booth wrote:

>> +  // See if the FP constant is top large for the integer.  For  
>> example,
>
> Typo.

Fixed.

>>   // Handle fcmp with constant RHS
>>   if (Constant *RHSC = dyn_cast<Constant>(Op1)) {
>> +    // If the constant is a nan, see if we can fold the comparison  
>> based on it.
>> +    if (ConstantFP *CFP = dyn_cast<ConstantFP>(RHSC)) {
>> +      if (CFP->getValueAPF().isNaN()) {
>> +        if (FCmpInst::isOrdered(I.getPredicate()))   // True if  
>> ordered and...
>> +          return ReplaceInstUsesWith(I,  
>> ConstantInt::get(Type::Int1Ty, 0));
>> +        if (FCmpInst::isUnordered(I.getPredicate())) // True if  
>> unordered or...
>> +          return ReplaceInstUsesWith(I,  
>> ConstantInt::get(Type::Int1Ty, 1));
>> +        if (FCmpInst::isUnordered(I.getPredicate())) // Undef on  
>> unordered.
>> +          return ReplaceInstUsesWith(I,  
>> UndefValue::get(Type::Int1Ty));
>> +
>
> Duplicate test?

Fixed.

>> +  // Okay, now we know that the FP constant fits in the range  
>> [SMIN, SMAX] but
>> +  // it may still be fractional.  See if it is fractional by  
>> casting the FP
>> +  // value to the integer value and back, checking for equality.   
>> Don't do this
>> +  // for zero, because -0.0 is not fractional.
>
> Perhaps this is better done as an APFloat method if I understand what
> you're trying to do?  It should be able to determine this reasonably
> easily without introducing allocations / conversions, though I've not
> thought about it a lot.

Yeah, I was meaning to ask you about this.  What is the best way of  
telling that an APFloat is fractional?  I could do the conversion back  
and forth and see if it is the same value, but that seems silly.  Is  
there a better way?

-Chris