[llvm-bugs] [Bug 49773] New: missed optimization for dead code elimination at -O3 (vs. -O2)

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=49773

            Bug ID: 49773
           Summary: missed optimization for dead code elimination at -O3
                    (vs. -O2)
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Interprocedural Optimizations
          Assignee: unassignedbugs at nondot.org
          Reporter: zhendong.su at inf.ethz.ch
                CC: llvm-bugs at lists.llvm.org

[637] % clangtk -v
clang version 13.0.0 (https://github.com/llvm/llvm-project.git
9fb0025f7084db14d16fe5cbe1d799f4ee0020af)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /local/suz-local/opfuzz/bin
Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/8
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/6
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/6.5.0
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
Candidate multilib: 32;@m32
Candidate multilib: x32;@mx32
Selected multilib: .;@m64
[638] % 
[638] % clangtk -O2 -S -o O2.s small.c
[639] % clangtk -O3 -S -o O3.s small.c
[640] % 
[640] % wc O2.s O3.s
  66  172 1711 O2.s
  82  213 2061 O3.s
 148  385 3772 total
[641] % 
[641] % grep foo O2.s
[642] % grep foo O3.s
        callq   foo
[643] % 
[643] % cat small.c
extern void foo(void);
static int a;
int **b, c, d, e;
int main() {
  if (a)
    foo();
  while (e)
    while (a++)
      while (c)
        *b = &d;
  return 0;
}

-- 
You are receiving this mail because:
You are on the CC list for the bug.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-bugs/attachments/20210330/632dc18b/attachment.html>