* [pushed] c++: don't do constexpr folding in unevaluated context
@ 2021-11-15 7:48 Jason Merrill
0 siblings, 0 replies; only message in thread
From: Jason Merrill @ 2021-11-15 7:48 UTC (permalink / raw)
To: gcc-patches
The implicit constexpr patch revealed that we were doing constant evaluation
of arbitrary expressions in unevaluated contexts, leading to failure when we
tried to evaluate e.g. a call to declval. This is wrong more generally;
only manifestly-constant-evaluated expressions should be evaluated within
an unevaluated operand.
Making this change revealed a case we were failing to mark as manifestly
constant-evaluated.
Tested x86_64-pc-linux-gnu, applying to trunk.
gcc/cp/ChangeLog:
* constexpr.c (maybe_constant_value): Don't evaluate
in an unevaluated operand unless manifestly const-evaluated.
(fold_non_dependent_expr_template): Likewise.
* decl.c (compute_array_index_type_loc): This context is
manifestly constant-evaluated.
---
gcc/cp/constexpr.c | 7 +++++++
gcc/cp/decl.c | 2 +-
2 files changed, 8 insertions(+), 1 deletion(-)
diff --git a/gcc/cp/constexpr.c b/gcc/cp/constexpr.c
index 7c27131f506..82a597d7bad 100644
--- a/gcc/cp/constexpr.c
+++ b/gcc/cp/constexpr.c
@@ -7696,6 +7696,10 @@ maybe_constant_value (tree t, tree decl, bool manifestly_const_eval)
return r;
}
+ /* Don't evaluate an unevaluated operand. */
+ if (cp_unevaluated_operand)
+ return t;
+
uid_sensitive_constexpr_evaluation_checker c;
r = cxx_eval_outermost_constant_expr (t, true, true, false, false, decl);
gcc_checking_assert (r == t
@@ -7759,6 +7763,9 @@ fold_non_dependent_expr_template (tree t, tsubst_flags_t complain,
return t;
}
+ if (cp_unevaluated_operand && !manifestly_const_eval)
+ return t;
+
tree r = cxx_eval_outermost_constant_expr (t, true, true,
manifestly_const_eval,
false, object);
diff --git a/gcc/cp/decl.c b/gcc/cp/decl.c
index 947bbfc6637..eed478199ea 100644
--- a/gcc/cp/decl.c
+++ b/gcc/cp/decl.c
@@ -11000,7 +11000,7 @@ compute_array_index_type_loc (location_t name_loc, tree name, tree size,
cp_convert (ssizetype, integer_one_node,
complain),
complain);
- itype = maybe_constant_value (itype);
+ itype = maybe_constant_value (itype, NULL_TREE, true);
}
if (!TREE_CONSTANT (itype))
base-commit: 267318a2857a42922c3ca033dac4690172b17683
--
2.27.0
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