[Bug tree-optimization/112296] __builtin_constant_p doesn't propagate through member functions

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112296

--- Comment #10 from Richard Biener <rguenth at gcc dot gnu.org> ---
Some history shows r0-31250-gb0b3afb2f34492 splitting this to the folding
code from RTL expansion of __builtin_constant_p where it previously was.
Even before r0-17364-gcff48d8f76463f we were simply doing

@@ -8566,10 +8579,34 @@ expand_builtin (exp, target, subtarget, mode, ignore)
          tree arg = TREE_VALUE (arglist);

          STRIP_NOPS (arg);
-         return (TREE_CODE_CLASS (TREE_CODE (arg)) == 'c'
-                 || (TREE_CODE (arg) == ADDR_EXPR
-                     && TREE_CODE (TREE_OPERAND (arg, 0)) == STRING_CST)
-                 ? const1_rtx : const0_rtx);

and that dates back to r0-384-gbbf6f052d786c2, "Initial revision" of expr.c
from Kenner :/