[Line Coverage] for loop which has empty predicate or true from <stdbool.h> as the predicate has wrong execution counters

[manvik99]

How to reproduce the bug ( Compiler explorer link: link )

cat > test.c << EOF
int main(){
    int x = 0;
    for (int i=0; ; i++)
    {
        if (x == 2){
            break;
        }
        x++;
    }
    return 0;
}
EOF
clang -fprofile-instr-generate -fcoverage-mapping -isystem. test.c -o test
./test
llvm-profdata merge default.profraw -o default.profdata
llvm-cov show -instr-profile default.profdata test

which would produce:

    1|      1|int main(){
    2|      1|    int x = 0;           // N1
    3|      2|    for (int i=0; ; i++) // N2-N1
    4|      3|    {                    // N2
    5|      3|        if (x == 2){
    6|      1|            break;
    7|      1|        }
    8|      2|        x++;
    9|      2|    }
   10|      1|    return 0;
   11|      1|}

The line before 'for' (Line number 2) has counter value N1.
The line after 'for' ( Line number 4) has counter value N2.
The line counter for 'for' ( Line number 3) is (N2-N1), which is hard to interpret.