[llvm-bugs] [Bug 44011] New: line coverage shows coverage of unreachable whitespace in switch statements

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=44011

            Bug ID: 44011
           Summary: line coverage shows coverage of unreachable whitespace
                    in switch statements
           Product: new-bugs
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: new bugs
          Assignee: unassignedbugs at nondot.org
          Reporter: hans at chromium.org
                CC: efriedma at quicinc.com, htmldeveloper at gmail.com,
                    llvm-bugs at lists.llvm.org, vsk at apple.com

Example:

$ cat /tmp/c.c
int main(int argc, char **argv) {
  switch (argc) {

  case 1:
    return 0;

  default:
    return 1;
  }
}

$ bin/clang -fcoverage-mapping -fprofile-instr-generate /tmp/c.c -Xclang
-dump-coverage-mapping && ./a.out && bin/llvm-profdata merge default.profraw -o
default.profdata && bin/llvm-cov show a.out -instr-profile=default.profdata
main:
  File 0, 1:33 -> 10:2 = #0
  File 0, 4:3 -> 5:13 = #2
  File 0, 7:3 -> 8:13 = #3
    1|      1|int main(int argc, char **argv) {
    2|      1|  switch (argc) {
    3|      1|
    4|      1|  case 1:
    5|      1|    return 0;
    6|      1|
    7|      1|  default:
    8|      0|    return 1;
    9|      1|  }
   10|      1|}


Note how lines 3 and 6 are shown as covered, even though control can never pass
through those lines.
Line 7 is also marked as executed, though a color terminal reveals it's only
the whitespace before "default" that was hit.

I think what's happening is that the whitespace inside the switch ends up in
region #0, which is used for the function body, which is obviously marked
executed.


Looking at https://bugs.llvm.org/show_bug.cgi?id=34612, perhaps the fix here is
to insert "gap" regions in between the switch cases. Or, would it work if we
emitted one big "gap" region for the whole switch body, kind of nested
underneath the regions for the cases?

+eli and +vedant who seem familiar with this area.



There are several similar bugs. I'm guessing most are due to the same problem:
https://bugs.llvm.org/show_bug.cgi?id=37072
https://bugs.llvm.org/show_bug.cgi?id=37124
https://bugs.llvm.org/show_bug.cgi?id=41821


(This was reported in Chromium: https://crbug.com/1024987)

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