[llvm-bugs] [Bug 51139] New: [regression] missed optimization for dead code elimination at -O3 (vs. -O2)

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=51139

            Bug ID: 51139
           Summary: [regression] missed optimization for dead code
                    elimination at -O3 (vs. -O2)
           Product: new-bugs
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: new bugs
          Assignee: unassignedbugs at nondot.org
          Reporter: theodoros.theodoridis at inf.ethz.ch
                CC: htmldeveloper at gmail.com, llvm-bugs at lists.llvm.org

$./bin/clang -v
clang version 13.0.0 (https://github.com/llvm/llvm-project.git
96d8f2a1e0842b83b319a8daf3cc82dd5e1350fa)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /dev/shm/llvm-project/build/./bin
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/10
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
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/9
Selected GCC installation: /usr/lib/gcc/x86_64-linux-gnu/10
Candidate multilib: .;@m64
Selected multilib: .;@m64
$cat test.c       
extern void foo(void);
extern void bar(void);
int a, b, d, e, f;
void g(int h);
static void c(int h) {
 g(b);
 while (1)
  while (a) {
   if (h)
    break;
   foo();
  }
}
void g(int h) {
 int i = 0;
 while (i < 1) {
  if (h)
   for (; i < 6; i++)
    ;
  while (d)
   while (f)
    while (e)
     bar();
 }
}
int main() {
 if (a)
  c(b);
 return 0;
}

$./bin/clang -O2 test.c -S -o O2.s     
$./bin/clang -O3 test.c -S -o O3.s     
$grep foo O2.s       
$grep foo O3.s   
        callq   foo



The commit which introduced this regression is f3a27511c9f8

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