*** Bug llvm/llvm-bugzilla-archive#10683 has been marked as a duplicate of this bug. ***

It has nothing to do with MFC though. Any file containing "//" with an empty line afterwards will cause a crash.

This code:
// \
int a; //dead line

Will be preprocessed as:
// int a; //dead line

Thus the second line is lost.

Fixed in r147091.

The bug is active in clang 3.6.2. This code:

int main(int argc, char* argv[]) {
//
int a; //dead line
int b;
return 0;
}

is preprocessed as:

int main(int argc, char* argv[]) {

int b;
return 0;

}

mentioned in issue llvm/llvm-bugzilla-archive#10683

Crash was indeed fixed in Clang 3.1: https://godbolt.org/z/cGrxoe5fn

As for the last example:

int main(int argc, char* argv[]) {
	// \
	int a; //dead line
	int b;
	return 0;
}

per N4944.lex.phases, backslashes are processed during the second phase, whereas comments are processed during the third phase. Which means int a; //dead line becomes a part of the previous line // before compiler recognizes comments to skip over them. There's no implementation divergence on this, save for MSVC /C (preserve comments) mode: https://godbolt.org/z/PYYhhdjKb