Tested x86_64-pc-linux-gnu, applying to trunk.
-- 8< --
In reviewing Nathaniel's patch for PR70331, it occurred to me that instead
of looking for various specific problematic things in the result of a
constexpr call to decide whether to cache it, we should use
reduced_constant_expression_p.
The change to that function is to avoid crashing on uninitialized objects of
non-class type.
In a trial version of this patch I checked to see what cases this stopped
caching; some were instances of partially-initialized return values, which
seem fine to not cache. Some were returning pointers to expiring local
variables, which we definitely want not to cache. And one was bit-cast3.C,
which will be handled in a follow-up patch.
gcc/cp/ChangeLog:
* constexpr.cc (cxx_eval_call_expression): Only cache
reduced_constant_expression_p results.
(reduced_constant_expression_p): Handle CONSTRUCTOR of scalar type.
(cxx_eval_constant_expression): Fold vectors here.
(cxx_eval_bare_aggregate): Not here.
---
gcc/cp/constexpr.cc | 17 +++++++++--------
1 file changed, 9 insertions(+), 8 deletions(-)
diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc
index c6f323ebf43..9d85c3be5cc 100644
--- a/gcc/cp/constexpr.cc
+++ b/gcc/cp/constexpr.cc
@@ -3033,7 +3033,7 @@ cxx_eval_call_expression (const constexpr_ctx *ctx, tree
t,
}
else
{
- bool cacheable = true;
+ bool cacheable = !!entry;
if (result && result != error_mark_node)
/* OK */;
else if (!DECL_SAVED_TREE (fun))
@@ -3185,7 +3185,7 @@ cxx_eval_call_expression (const constexpr_ctx *ctx, tree
t,
for the constexpr evaluation and should not be cached.
It is fine if the call allocates something and deallocates it
too. */
- if (entry
+ if (cacheable
&& (save_heap_alloc_count != ctx->global->heap_vars.length ()
|| (save_heap_dealloc_count
!= ctx->global->heap_dealloc_count)))
@@ -3204,10 +3204,6 @@ cxx_eval_call_expression (const constexpr_ctx *ctx, tree
t,
cacheable = false;
break;
}
- /* Also don't cache a call that returns a deallocated pointer. */
- if (cacheable && (cp_walk_tree_without_duplicates
- (&result, find_heap_var_refs, NULL)))
- cacheable = false;
}
/* Rewrite all occurrences of the function's RESULT_DECL with the
@@ -3217,6 +3213,10 @@ cxx_eval_call_expression (const constexpr_ctx *ctx, tree
t,
&& !is_empty_class (TREE_TYPE (res)))
if (replace_decl (&result, res, ctx->object))
cacheable = false;
+
+ /* Only cache a permitted result of a constant expression. */
+ if (cacheable && !reduced_constant_expression_p (result))
+ cacheable = false;
}
else
/* Couldn't get a function copy to evaluate. */
@@ -3268,8 +3268,9 @@ reduced_constant_expression_p (tree t)
case CONSTRUCTOR:
/* And we need to handle PTRMEM_CST wrapped in a CONSTRUCTOR. */
tree field;
- if (TREE_CODE (TREE_TYPE (t)) == VECTOR_TYPE)
- /* An initialized vector would have a VECTOR_CST. */
+ if (!AGGREGATE_TYPE_P (TREE_TYPE (t)))
+ /* A constant vector would be folded to VECTOR_CST.
+ A CONSTRUCTOR of scalar type means uninitialized. */
return false;
if (CONSTRUCTOR_NO_CLEARING (t))
{
base-commit: caabf0973a4e9a26421c94d540e3e20051e93e77
--
2.39.3
