On Tue, Sep 12, 2023 at 05:26:25PM -0400, Jason Merrill wrote:
> On 9/8/23 14:24, Marek Polacek wrote:
> > + if (!in_immediate_context ()
> > + /* P2564: a subexpression of a manifestly constant-evaluated
> > expression
> > +or conversion is an immediate function context. */
> > + && ctx->manifestly_const_eval != mce_true
>
> I might check this first as a tiny optimization.
Done.
> > + switch (TREE_CODE (stmt))
> > +{
> > +/* Unfortunately we must handle code like
> > +false ? bar () : 42
> > + where we have to check bar too. */
> > +case COND_EXPR:
> > + if (cp_fold_immediate_r (_OPERAND (stmt, 1), walk_subtrees,
> > data))
> > + return error_mark_node;
> > + if (TREE_OPERAND (stmt, 2)
> > + && cp_fold_immediate_r (_OPERAND (stmt, 2), walk_subtrees, data))
> > + return error_mark_node;
>
> Is this necessary? Doesn't walk_tree already walk into the arms of
> COND_EXPR?
Unfortunately yes. The cp_fold call in cp_fold_r could fold the ?: into
a constant before we see it here. I've added a comment saying just that.
> > + break;
> > +
> > case PTRMEM_CST:
> > if (TREE_CODE (PTRMEM_CST_MEMBER (stmt)) == FUNCTION_DECL
> > && DECL_IMMEDIATE_FUNCTION_P (PTRMEM_CST_MEMBER (stmt)))
> > {
> > - if (!data->pset.add (stmt))
> > + if (!data->pset.add (stmt) && (complain & tf_error))
> > error_at (PTRMEM_CST_LOCATION (stmt),
> > "taking address of an immediate function %qD",
> > PTRMEM_CST_MEMBER (stmt));
> > stmt = *stmt_p = build_zero_cst (TREE_TYPE (stmt));
>
> It looks like this will overwrite *stmt_p even if we didn't give an error.
I suppose that could result in missing errors, adjusted. And there's no
point in setting stmt.
> > - break;
> > + return error_mark_node;
> > }
> > break;
> > +/* Expand immediate invocations. */
> > +case CALL_EXPR:
> > +case AGGR_INIT_EXPR:
> > + if (tree fn = cp_get_callee (stmt))
> > + if (TREE_CODE (fn) != ADDR_EXPR || ADDR_EXPR_DENOTES_CALL_P (fn))
> > + if (tree fndecl = cp_get_fndecl_from_callee (fn, /*fold*/false))
> > + if (DECL_IMMEDIATE_FUNCTION_P (fndecl))
> > + {
> > + *stmt_p = stmt = cxx_constant_value (stmt, complain);
>
> Likewise.
I think we have to keep setting *stmt_p to actually evaluate consteval
functions. But again, no need to set stmt.
> > + if (stmt == error_mark_node)
> > + return error_mark_node;
> > + }
> > + break;
> > +
> > case ADDR_EXPR:
> > if (TREE_CODE (TREE_OPERAND (stmt, 0)) == FUNCTION_DECL
> > && DECL_IMMEDIATE_FUNCTION_P (TREE_OPERAND (stmt, 0)))
> > {
> > - error_at (EXPR_LOCATION (stmt),
> > - "taking address of an immediate function %qD",
> > - TREE_OPERAND (stmt, 0));
> > + if (complain & tf_error)
> > + error_at (EXPR_LOCATION (stmt),
> > + "taking address of an immediate function %qD",
> > + TREE_OPERAND (stmt, 0));
> > stmt = *stmt_p = build_zero_cst (TREE_TYPE (stmt));
>
> Likewise.
Adjusted like case PTRMEM_CST.
Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
-- >8 --
In the review of P2564:
it turned out that in order to correctly handle an example in the paper,
we should stop doing immediate evaluation in build_over_call and
bot_replace, and instead do it in cp_fold_r. This patch does that.
Another benefit is that this is a pretty significant simplification, at
least in my opinion. Also, this fixes the c++/110997 ICE (but the test
doesn't compile yet).
The main drawback seems to be that cp_fold_r doesn't process
uninstantiated templates. We still have to handle things like
"false ? foo () : 1". To that end, I've added cp_fold_immediate, called
on dead branches in cxx_eval_conditional_expression. Since in cxx_*
I can't rely on current_function_decl being available, I've added
another walk: a new overload for in_immediate_context that looks into
constexpr_ctx.
You'll see that I've reintroduced ADDR_EXPR_DENOTES_CALL_P here. This
is to detect
*()) ()
(s.*::foo) ()
which were deemed ill-formed.
gcc/cp/ChangeLog:
* call.cc (in_immediate_context): No longer static.
(build_over_call): Set ADDR_EXPR_DENOTES_CALL_P. Don't handle
immediate_invocation_p here.
* constexpr.cc (in_immediate_context): New overload.
(cxx_eval_call_expression): Use mce_true for DECL_IMMEDIATE_FUNCTION_P.
(cxx_eval_conditional_expression): Call cp_fold_immediate.
* cp-gimplify.cc (maybe_replace_decl): Make static.
(cp_fold_r): Expand immediate invocations.
(cp_fold_immediate_r): New.
(cp_fold_immediate): New.
* cp-tree.h (ADDR_EXPR_DENOTES_CALL_P): Define.
(cp_fold_immediate): Declare.
* tree.cc
