[llvm-bugs] [Bug 49423] New: [LLVM-COV] Label in switch statement and dead code were wrongly marked as executed

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=49423

            Bug ID: 49423
           Summary: [LLVM-COV] Label in switch statement and dead code
                    were wrongly marked as executed
           Product: Runtime Libraries
           Version: 11.0
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: libprofile library
          Assignee: unassignedbugs at nondot.org
          Reporter: cnwy1996 at outlook.com
                CC: llvm-bugs at lists.llvm.org

$ clang -v
clang version 11.0.0
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /home/wangyang/llvm-project/build/bin
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7.5.0
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/8
Selected GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7.5.0
Candidate multilib: .;@m64
Selected multilib: .;@m64

$ cat test.c
#include<stdio.h>
int *ptr;
struct a {
  int c;
};
int main(int argc, char **argv) {
  struct a e;
  e.c = 2;
  int x = 0;
  for (;;)
    switch (e.c)
    case 3: {
      printf("1");
      int resxxx;
    case 2:
      ptr = &resxxx;
      *ptr = 123;
      if (x)
        return 0;
      else
        x = 1;
    }
      printf("2");
      return 1;
}

$ clang -w -O0 -g -fcoverage-mapping -fprofile-instr-generate=test.profraw
test.c; ./a.out; llvm-profdata merge test.profraw -o test.profdata; llvm-cov
show a.out -instr-profile=test.profdata test.c > test.lcov; cat test.lcov
    1|       |#include<stdio.h>
    2|       |int *ptr;
    3|       |struct a {
    4|       |  int c;
    5|       |};
    6|      1|int main(int argc, char **argv) {
    7|      1|  struct a e;
    8|      1|  e.c = 2;
    9|      1|  int x = 0;
   10|      1|  for (;;)
   11|      2|    switch (e.c)
   12|      2|    case 3: {
   13|      0|      printf("1");
   14|      0|      int resxxx;
   15|      2|    case 2:
   16|      2|      ptr = &resxxx;
   17|      2|      *ptr = 123;
   18|      2|      if (x)
   19|      1|        return 0;
   20|      1|      else
   21|      1|        x = 1;
   22|      2|    }
   23|      1|      printf("2");
   24|      0|      return 1;
   25|      1|}
   26|       |

Line 12 and 23 were actually not executed.

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