[Bug tree-optimization/100510] New: bogus -Wvla-large-than with -Walloca

[msebor at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100510

            Bug ID: 100510
           Summary: bogus -Wvla-large-than with -Walloca
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: msebor at gcc dot gnu.org
  Target Milestone: ---

The VLA below is at most 32 bytes large but with both -Walloca and
-Wvla-larger-than= GCC issues a -Wvla-larger-than false positive, both with and
without optimization.

$ cat a.c && gcc -Walloca  -S -Wvla-larger-than=1000 a.c
void f (void*);

void g (__SIZE_TYPE__ n)
{
  if (n > 32)
    return;

  char a[n];
  f (a);
}

a.c: In function ‘g’:
a.c:8:8: warning: unbounded use of variable-length array [-Wvla-larger-than=]
    8 |   char a[n];
      |        ^