I’m trying to find all the implicit casts in a program compiled with llvm-gcc. What I’ve been doing is for each function taking all the instruction and going through each of their operands (and the opreands of their operands etc…) and checking to see if any are an instance of UnaryConstantExpr. When I encounter such an instance, I determine whether the type of that value and its 0th operand differ, if they do its an implicit cast. I do basically the same procedure for the the global variables. Is this the best approach to take or is there a better way of going about this?
I’ve asked at least a few questions on this mailing-list and you have all been VERY helpful. Thank you all so much.
I'm trying to find all the implicit casts in a program compiled with
llvm-gcc.
I'm not sure exactly what you're trying to do here. In particular, llvm-gcc will turn any casts that are implicit in the C code into explicit casts in the LLVM... which means that there is no good way to tell the difference between an implicit or explicit cast.
What I've been doing is for each function taking all the
instruction and going through each of their operands (and the opreands of
their operands etc...) and checking to see if any are an instance of
UnaryConstantExpr. When I encounter such an instance, I determine whether
the type of that value and its 0th operand differ, if they do its an
implicit cast. I do basically the same procedure for the the global
variables. Is this the best approach to take or is there a better way of
going about this?
I'm not sure I follow here. It sounds like you are detecting things like:
short A = ...
int B = ...
int C = (int)A + B;
However, there isn't a way to tell if the "(int)" was implicit or explicit.
I've asked at least a few questions on this mailing-list and you haveall
been VERY helpful. Thank you all so much.
-Chris
Err… Your right. What about just finding casts in general.
Err.. Your right. What about just finding casts in general.
Two separate issues: cast instructions and cast constant expressions.
You can find cast instructions by looping through all the instructions, and using "isa<CastInst>(I)". To find cast constant expressions, you'd use basically what you describe below: loop through globals and instructions, checking the operands to see if they are constant expression casts.
-Chris