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

[Daniel Marjamäki via cfe-dev]

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
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