[llvm-bugs] [Bug 25631] New: failure to remove redundant global without 'norecurse'

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=25631

            Bug ID: 25631
           Summary: failure to remove redundant global without 'norecurse'
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: Core LLVM classes
          Assignee: unassignedbugs at nondot.org
          Reporter: richard-llvm at metafoo.co.uk
                CC: llvm-bugs at lists.llvm.org
    Classification: Unclassified

In bug#25629, we have this testcase:

int printf (const char *, ...); 

int a, d; 
static char b = 48, c;

int
main ()
{
  c = b;
  for (; c < 45; c++)
    a = a ? d : d < a;
  b = 0;
  printf ("%d\n", c);
  return 0;
}

When built as C++, we can completely delete the global variable 'c'. When built
as C++, we cannot. The difference is that 'main' is implicitly 'norecurse' in
C++.

It should be possible to do the same optimization whether or not 'main' is
marked 'norecurse' -- within the entire program, there are only stores and no
loads to @c.

(Running opt over the output a second time results in @c being removed.)

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