[Bug c++/71372] [6/7 Regression] C++ FE drops TREE_THIS_VOLATILE in cp_fold on all tcc_reference trees

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71372

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
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                 CC|                            |jakub at gcc dot gnu.org

--- Comment #6 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Isn't this generally a problem of the whole folder, not just cp_fold?
I mean, if you have say
MEM[&MEM[p, CST1], CST2]
and the outer MEM_REF has e.g. TREE_THIS_VOLATILE, TREE_THIS_NOTRAP,
TREE_SIDE_EFFECTS, TREE_READONLY, TREE_CONSTANT set on it, and you call fold on
it, then I don't see what would preserve those bits (not sure if all of them
are applicable).
I see just
      switch (TREE_CODE_LENGTH (code))
        {
        case 1:
          op0 = TREE_OPERAND (t, 0);
          tem = fold_unary_loc (loc, code, type, op0);
          return tem ? tem : expr;
        case 2:
          op0 = TREE_OPERAND (t, 0);
          op1 = TREE_OPERAND (t, 1);
          tem = fold_binary_loc (loc, code, type, op0, op1);
          return tem ? tem : expr;
        case 3:
          op0 = TREE_OPERAND (t, 0);
          op1 = TREE_OPERAND (t, 1);
          op2 = TREE_OPERAND (t, 2);
          tem = fold_ternary_loc (loc, code, type, op0, op1, op2);
          return tem ? tem : expr;
without really trying to preserve anything.  Similarly to this cp_fold has
similar problem, c_fully_fold* will work more often than cp_fold, because it
always goes through build instead of fold_build*, followed by copying over of
TREE_THIS_VOLATILE and various other flags, and only then calls fold on the
whole result, so just for the tem != NULL cases above can drop the flags, but
in cp_fold it always calls fold_build* without copying flags over.

Now, the question is, if what we should do here and cp_fold is not fold at all
for TREE_THIS_VOLATILE (in cp_fold then just build and copy over flags), or
fold, check if the result of the folding is still e.g. tcc_reference, and just
set the flag on the result if it has been set before.