[llvm-dev] Highlight taken LLVM IR branches in a real execution environment

[Jameson Nash via llvm-dev]

It sounds a bit like you're looking for code-coverage (and in particular
branch-coverage)? ie.
https://clang.llvm.org/docs/SourceBasedCodeCoverage.html#branch-regions Or
other fuzzer frameworks, such as using concolic testing?

On Fri, Feb 26, 2021 at 11:08 AM Johannes Doerfert via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> Could you elaborate what you mean with "mark" here?
>
> You want to create a flow sensitive static analysis or profile which
> branch has been taken at runtime, or both?
>
> FWIW, if you tell LLVM x > 0, e.g., `__builtin_assume(x > 0)` in your
> source,
> the branches should be folded away.
>
> ~ Johannes
>
>
> On 2/26/21 9:15 AM, Joseph via llvm-dev wrote:
> > Hey. I realize this question is a bit out-of-place, but I feel someone in
> > the LLVM community might've ran into a similar topic before.
> >
> > I'd like to find a way to run LLVM IR and mark all branches taken, given
> a
> > specific input.
> >
> > Take this example:
> >
> > ```
> > int get_sign(int x) {
> > if (x == -1234) return -1234;
> > if (x < 0) return -1;
> > else return 1;
> > }
> > ```
> >
> > It's clear that the `x == -1234` branch is useless if x > 0. Does the
> LLVM
> > project have a way of marking the taken branches, so that one can reason
> > about them later, possibly in an LLVM pass?
> >
> > I do realize KLEE exists, but SMT solvers require quite a bit of
> "plugging"
> > of functions to limit the scope. Not to mention the path explosion that a
> > real binary would entail. What I was looking for was possibly an lldb/lli
> > mechanism to allow "marking" the taken branches, in a real execution
> > environment.
> >
> > Has someone encountered such an issue before?
> >
> > Many thanks
> >
> > -- J
> >
> >
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