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| author | Patrick Palka <ppalka@redhat.com> | 2023-11-15 12:03:16 -0500 |
|---|---|---|
| committer | Patrick Palka <ppalka@redhat.com> | 2023-11-15 12:03:16 -0500 |
| commit | 6665a8572c8f24bd55c6081c91f461442c94dcfb (patch) | |
| tree | cac5a0d267e871406728301433a870e46ff3b5b6 /gcc/cp/constexpr.cc | |
| parent | 93d85b80605aa787d2cc103e7a70d10487c01bea (diff) | |
| download | gcc-6665a8572c8f24bd55c6081c91f461442c94dcfb.zip gcc-6665a8572c8f24bd55c6081c91f461442c94dcfb.tar.gz gcc-6665a8572c8f24bd55c6081c91f461442c94dcfb.tar.bz2 | |
c++: constantness of local var in constexpr fn [PR111703, PR112269]
potential_constant_expression was incorrectly treating most local
variables from a constexpr function as constant because it wasn't
considering the 'now' parameter. This patch fixes this by relaxing
its var_in_maybe_constexpr_fn checks accordingly, which turns out to
partially fix two recently reported regressions:
PR111703 is a regression caused by r11-550-gf65a3299a521a4 for restricting
constexpr evaluation during warning-dependent folding. The mechanism is
intended to restrict only constant evaluation of the instantiated
non-dependent expression, but it also ends up restricting constant
evaluation occurring during instantiation of the expression, in particular
when instantiating the converted argument 'x' (a VIEW_CONVERT_EXPR) into
a copy constructor call. This seems like a flaw in the mechanism, though
I don't know if we want to fix the mechanism or get rid of it completely
since the original testcases which motivated the mechanism are fixed more
simply by r13-1225-gb00b95198e6720. In any case, this patch partially
fixes this by making us correctly treat 'x' as non-constant which prevents
the problematic warning-dependent folding from occurring at all.
PR112269 is caused by r14-4796-g3e3d73ed5e85e7 for merging tsubst_copy
into tsubst_copy_and_build. tsubst_copy used to exit early when 'args'
was empty, behavior which that commit deliberately didn't preserve.
This early exit masked the fact that COMPLEX_EXPR wasn't handled by
tsubst at all, and is a tree code that apparently we could see during
warning-dependent folding on some targets. A complete fix is to add
handling for this tree code in tsubst_expr, but this patch should fix
the reported testsuite failures since the COMPLEX_EXPRs that crop up
in <complex> are considered non-constant expressions after this patch.
PR c++/111703
PR c++/112269
gcc/cp/ChangeLog:
* constexpr.cc (potential_constant_expression_1) <case VAR_DECL>:
Only consider var_in_maybe_constexpr_fn if 'now' is false.
<case INDIRECT_REF>: Likewise.
gcc/testsuite/ChangeLog:
* g++.dg/cpp2a/concepts-fn8.C: New test.
Diffstat (limited to 'gcc/cp/constexpr.cc')
| -rw-r--r-- | gcc/cp/constexpr.cc | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc index c05760e..8a6b210 100644 --- a/gcc/cp/constexpr.cc +++ b/gcc/cp/constexpr.cc @@ -9623,7 +9623,7 @@ potential_constant_expression_1 (tree t, bool want_rval, bool strict, bool now, return RECUR (DECL_VALUE_EXPR (t), rval); } if (want_rval - && !var_in_maybe_constexpr_fn (t) + && (now || !var_in_maybe_constexpr_fn (t)) && !type_dependent_expression_p (t) && !decl_maybe_constant_var_p (t) && (strict @@ -9737,7 +9737,7 @@ potential_constant_expression_1 (tree t, bool want_rval, bool strict, bool now, STRIP_NOPS (x); if (is_this_parameter (x) && !is_capture_proxy (x)) { - if (!var_in_maybe_constexpr_fn (x)) + if (now || !var_in_maybe_constexpr_fn (x)) { if (flags & tf_error) constexpr_error (loc, fundef_p, "use of %<this%> in a " |