llvm-cov: wrong coverage for the "for-expression"


Bugzilla Link	PR45846
Status	CONFIRMED
Importance	P normal
Reported by	Yibiao Yang (yangyibiao@nju.edu.cn)
Reported on	2020-05-08 10:37:36 -0700
Last modified on	2020-12-16 23:20:23 -0800
Version	trunk
Hardware	PC Linux
CC	dblaikie@gmail.com, llvm-bugs@lists.llvm.org
Fixed by commit(s)
Attachments
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Blocked by
See also

$ clang --version
clang version 11.0.0 (/home/yibiao/.cache/yay/llvm-git/llvm-project
871beba234a83a2a02da9dedbd59b91a1bfbd7af)
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/bin

$ clang -O0 -w -fcoverage-mapping -fprofile-instr-generate=small.profraw
small.c; ./a.out; llvm-profdata merge small.profraw -o small.profdata; llvm-cov
show a.out -instr-profile=small.profdata small.c > small.c.lcov; cat
small.c.lcov
    1|      1|void ok() { exit(0); }
    2|       |
    3|      1|void foo() {
    4|      1|  int i;
    5|      2|  for (i=1; 1>0; ++i)
    6|      1|    ok();
    7|      1|}
    8|       |
    9|      1|int main() {
   10|      1|  foo();
   11|      1|}

***
Line 5 is wrongly marked as executed twice. However, when called ok, the
program is exit. Thus, the for expression should be executed only once. When
setting breakpoint for Line 5 in LLDB, it only hit one time as follow:
$ clang -w -g small.c; lldb a.out
(lldb) target create "a.out"
Current executable set to '/home/yibiao/Decov/a.out' (x86_64).
(lldb) b 5
Breakpoint 1: where = a.out`foo + 8 at small.c:5:9, address = 0x0000000000401148
(lldb) r
Process 447035 launched: '/home/yibiao/Decov/a.out' (x86_64)
Process 447035 stopped
* thread #1, name = 'a.out', stop reason = breakpoint 1.1
    frame #0: 0x0000000000401148 a.out`foo at small.c:5:9
   2
   3    void foo() {
   4      int i;
-> 5      for (i=1; 1>0; ++i)
   6        ok();
   7    }
   8
(lldb) c
Process 447035 resuming
Process 447035 exited with status = 0 (0x00000000)

When we replace Line 6 with "exit(0); // ok();", the coverage is correct as
follow:

    1|      0|void ok() { exit(0); }
    2|       |
    3|      1|void foo() {
    4|      1|  int i;
    5|      1|  for (i=1; 1>0; ++i)
    6|      1|    exit(0); // ok();
    7|      1|}
    8|       |
    9|      1|int main() {
   10|      1|  foo();
   11|      1|}

$ cat small.c
void ok() { exit(0); }

void foo() {
  int i;
  for (i=1; 1>0; ++i)
    ok();
}

int main() {
  foo();
}

Quuxplusone / LLVMBugzillaTest

llvm-cov: wrong coverage for the "for-expression" #44816