[llvm-commits] CVS: llvm/lib/Analysis/ScalarEvolution.cpp

[Chris Lattner]

On Dec 5, 2006, at 11:58 AM, Reid Spencer wrote:
> On Tue, 2006-12-05 at 11:52 -0800, Chris Lattner wrote:
>>>  SCEVHandle SCEVTruncateExpr::get(const SCEVHandle &Op, const Type
>>> *Ty) {
>>>    if (SCEVConstant *SC = dyn_cast<SCEVConstant>(Op))
>>> -    return SCEVUnknown::get(ConstantExpr::getCast(SC->getValue(),
>>> Ty));
>>> +    return SCEVUnknown::get(
>>> +        ConstantExpr::getTruncOrBitCast(SC->getValue(), Ty));
>>
>> Shouldn't this one always bit a truncate?
>
> No, they could be the same size.

How?  The two call sites are:

   if (SrcTy->getPrimitiveSize() > Ty->getPrimitiveSize())
     return SCEVTruncateExpr::get(V, Ty);

and:

     case Instruction::Trunc:
       if (I->getType()->isInteger() && I->getOperand(0)->getType()- 
 >isInteger())
         return SCEVTruncateExpr::get(getSCEV(I->getOperand(0)),
                                      I->getType()->getUnsignedVersion 
());

The first can't be the same size, obviously.  The second can't be the  
same size because it's coming from a trunc instruction.  Further, the  
'I->getOperand(0)->getType()->isInteger()' in the second code is also  
redundant with 'truncness'.

>>
>>>  SCEVHandle SCEVZeroExtendExpr::get(const SCEVHandle &Op, const
>>> Type *Ty) {
>>>    if (SCEVConstant *SC = dyn_cast<SCEVConstant>(Op))
>>> -    return SCEVUnknown::get(ConstantExpr::getCast(SC->getValue(),
>>> Ty));
>>> +    return SCEVUnknown::get(
>>> +        ConstantExpr::getZExtOrBitCast(SC->getValue(), Ty));
>>
>> Likewise, always a zext?
>
> No, they could be the same size.

This is called in two places very similar to trunc.

If you believe that these can be called with srcsize=destsize, please  
explain how.

>>
>>> @@ -998,11 +1000,10 @@
>>>        Constant *LHSCV = LHSC->getValue();
>>>        Constant *RHSCV = RHSC->getValue();
>>>        if (LHSCV->getType()->isUnsigned())
>>> -        LHSCV = ConstantExpr::getInferredCast(
>>> -            LHSCV, false, LHSCV->getType()->getSignedVersion(),
>>> true);
>>> +        LHSCV = ConstantExpr::getBitCast(LHSCV,
>>> +                                         LHSCV->getType()-
>>>> getSignedVersion());
>>>        if (RHSCV->getType()->isUnsigned())
>>> -        RHSCV = ConstantExpr::getInferredCast(
>>> -            RHSCV, false, LHSCV->getType(), true);
>>> +        RHSCV = ConstantExpr::getBitCast(RHSCV, LHSCV->getType());
>>>        return SCEVUnknown::get(ConstantExpr::getSDiv(LHSCV, RHSCV));
>>>      }
>>>    }
>>
>> As I mentioned before, these casts can all go away.  sdiv is signless
>> now.
>
> One thing at a time.  This patch is getting rid of getInferredCast and
> no more.

Fair enough, please make sure it happens at some point though.

-Chris