[Bug gcov-profile/115047] Inconsistent MC/DC reported by GCC and LLVM

[j at lambda dot is via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115047

--- Comment #4 from Jørgen Kvalsvik  ---
> I guess it would be desirable to (1) let LLVM support masking MC/DC and (2) 
> let
gcov support unique-cause MC/DC. The first seems easier and I might try
implementing a prototype.

There is room for both, e.g. -fcondition-coverage={masking,unique} or similar.
I don't think supporting unique cause MC/DC would be too hard in GCC either,
using a method similar to GCC's upcoming path coverage and LLVM's MC/DC, if it
is desirable.

[Bug gcov-profile/115047] Inconsistent MC/DC reported by GCC and LLVM

[j at lambda dot is via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115047

--- Comment #2 from Jørgen Kvalsvik  ---
> f(1, 0, 0) = false, while f(1, 0, 1) = true

Sorry, I meant:

f(0, 0, 1) = true
f(0, 0, 0) = false
and
f(1, 0, 1) = true
f(1, 0, 0) = false

It does not take away from the conclusion when doing masking MC/DC.

[Bug gcov-profile/115047] Inconsistent MC/DC reported by GCC and LLVM

[j at lambda dot is via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115047

--- Comment #1 from Jørgen Kvalsvik  ---
gcc is not wrong here - f(1, 0, 0) = false, while f(1, 0, 1) = true so clearly
c has an independent effect on the outcome here, and both its values has been
observed.

I think clang measures unique-cause and not masking MC/DC which probably
explains the difference (at least clang's documentation [1] does not specify
which form it measures. Since more than one variable change between the two
test vectors I assume that would be it. I don't have clang 19 available right
now, does f(0, 0, 1); f(0, 0, 0); cover c?

[1]
https://clang.llvm.org/docs/SourceBasedCodeCoverage.html#mc-dc-instrumentation