[cfe-dev] Checking For The Overflow Of An Expr In A ASTMatcher

[Farzad Sadeghi via cfe-dev]

its solved now. I was matching the same expr more than once without
realizing, so i was looking at the result from a different part of the
same expr.

On 1/9/17, Daniel Marjamäki <Daniel.Marjamaki at evidente.se> wrote:
>
> I don't know why you get 0xFFFFFFFF from getExtValue(). I get 0.
>
>     B->dump();
>
>     llvm::APSInt Result;
>     B->EvaluateAsInt(Result, AC->getASTContext());
>     Result.dump();
>
>     llvm::APSInt LVal;
>     B->getLHS()->EvaluateAsInt(LVal, AC->getASTContext());
>
>     __int64 x = Result.getExtValue();  // <- x=0
>     bool y = Result < LVal; // <- y=true
>
>
> Best regards,
> Daniel Marjamäki
>
> ..................................................................................................................
> Daniel Marjamäki Senior Engineer
> Evidente ES East AB  Warfvinges väg 34  SE-112 51 Stockholm  Sweden
>
> Mobile:                 +46 (0)709 12 42 62
> E-mail:                 Daniel.Marjamaki at evidente.se
>
> www.evidente.se
>
> ________________________________________
> From: Farzad Sadeghi [thabogre at gmail.com]
> Sent: 09 January 2017 12:09
> To: Daniel Marjamäki
> Cc: cfe-dev
> Subject: Re: [cfe-dev] Checking For The Overflow Of An Expr In A ASTMatcher
>
> My dump also shows the same thing:
> ParenExpr 0x30debe0 'unsigned int'
> `-BinaryOperator 0x30debb8 'unsigned int' '+'
>   |-IntegerLiteral 0x30deb78 'unsigned int' 2147483648
>   `-IntegerLiteral 0x30deb98 'unsigned int' 2147483648
> APInt(32b, 0u 0s)
>
> but when i use getExtValue() it returns 0xFFFFFFFF which is not a
> wrap-around.
> maybe i shouldnt get the value like that?
>
> On 1/9/17, Daniel Marjamäki <Daniel.Marjamaki at evidente.se> wrote:
>>
>> Hello!
>>
>> It sounds strange that you get a saturated value.
>>
>> try this code:
>>
>>     B->dump();
>>
>>     llvm::APSInt Result;
>>     B->EvaluateAsInt(Result, AC->getASTContext());
>>     Result.dump();
>>
>> My output is:
>>
>>     BinaryOperator 0x651b98 'unsigned int' '+'
>>     |-IntegerLiteral 0x651b58 'unsigned int' 2147483648
>>     `-IntegerLiteral 0x651b78 'unsigned int' 2147483648
>>
>>     APInt(32b, 0u 0s)
>>
>> Here it can be seen that there has been an overflow since the result is
>> less
>> than the operands.
>>
>> Best regards,
>> Daniel Marjamäki
>>
>> ..................................................................................................................
>> Daniel Marjamäki Senior Engineer
>> Evidente ES East AB  Warfvinges väg 34  SE-112 51 Stockholm  Sweden
>>
>> Mobile:                 +46 (0)709 12 42 62
>> E-mail:                 Daniel.Marjamaki at evidente.se
>>
>> www.evidente.se
>>
>> ________________________________________
>> From: cfe-dev [cfe-dev-bounces at lists.llvm.org] on behalf of Farzad Sadeghi
>> via cfe-dev [cfe-dev at lists.llvm.org]
>> Sent: 09 January 2017 09:13
>> To: cfe-dev
>> Subject: [cfe-dev] Checking For The Overflow Of An Expr In A ASTMatcher
>>
>> Hi,
>> I have two questions.
>> I wan to check for overflows in an ASTMatcher.
>> I only need to check for Exprs that are of type Int, so I figured I
>> could use Expr::EvaluateAsInt.
>> I have the following code:
>>
>> #define START 0x80000000
>> #define END 0xFFFFFFFF
>> #define LEN 0x80000000
>>
>> if ((START + LEN) > END)
>> {
>>    /*does something*/
>> }
>>
>> Int size on my target(x86-64) is 32-bits so obviously START + LEN
>> should overflow.
>> when i call the APSInt.getExtValue() I get 4294967295 which has
>> overflowed and saturated. The type of the Expr is Int so the result is
>> saturated and then when i extend it with getExtValue its not going to
>> give me 4294967296 obviously.
>> My question is, is there a way to cast the result of the evaluation to
>> a wider type before it gets truncated?
>>
>> I also thought i could use Expr::EvaluateForOverflow( const
>> ASTContext) but i cant figure out how it works.  My question is How
>> does it return a value I can check for?
>> The return type is void so i figured maybe its setting a flag
>> somewhere but I couldnt find it. I looked at Expr's attributes but no
>> luck. I thought maybe ASTContext holds the result but I couldn't find
>> anything there either.
>>
>> --
>> Farzad Sadeghi
>> project mutator-https://github.com/bloodstalker/mutator
>> _______________________________________________
>> cfe-dev mailing list
>> cfe-dev at lists.llvm.org
>> http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev
>>
>
>
> --
> Farzad Sadeghi
> project mutator-https://github.com/bloodstalker/mutator
>


-- 
Farzad Sadeghi
project mutator-https://github.com/bloodstalker/mutator