* [PATCH RFA (fold)] c++: constexpr bit_cast with empty field
@ 2023-07-17 21:19 Jason Merrill
2023-07-18 11:31 ` Richard Biener
0 siblings, 1 reply; 3+ messages in thread
From: Jason Merrill @ 2023-07-17 21:19 UTC (permalink / raw)
To: gcc-patches
Tested x86_64-pc-linux-gnu, OK for trunk?
-- 8< --
The change to only cache constexpr calls that are
reduced_constant_expression_p tripped on bit-cast3.C, which failed that
predicate due to the presence of an empty field in the result of
native_interpret_aggregate, which reduced_constant_expression_p rejects to
avoid confusing output_constructor.
This patch proposes to skip such fields in native_interpret_aggregate, since
they aren't actually involved in the value representation.
gcc/ChangeLog:
* fold-const.cc (native_interpret_aggregate): Skip empty fields.
gcc/cp/ChangeLog:
* constexpr.cc (cxx_eval_bit_cast): Check that the result of
native_interpret_aggregate doesn't need more evaluation.
---
gcc/cp/constexpr.cc | 9 +++++++++
gcc/fold-const.cc | 3 ++-
2 files changed, 11 insertions(+), 1 deletion(-)
diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc
index 9d85c3be5cc..6e8f1c2b61e 100644
--- a/gcc/cp/constexpr.cc
+++ b/gcc/cp/constexpr.cc
@@ -1440,6 +1440,8 @@ enum value_cat {
static tree cxx_eval_constant_expression (const constexpr_ctx *, tree,
value_cat, bool *, bool *, tree * = NULL);
+static tree cxx_eval_bare_aggregate (const constexpr_ctx *, tree,
+ value_cat, bool *, bool *);
static tree cxx_fold_indirect_ref (const constexpr_ctx *, location_t, tree, tree,
bool * = NULL);
static tree find_heap_var_refs (tree *, int *, void *);
@@ -4803,6 +4805,13 @@ cxx_eval_bit_cast (const constexpr_ctx *ctx, tree t, bool *non_constant_p,
{
clear_type_padding_in_mask (TREE_TYPE (t), mask);
clear_uchar_or_std_byte_in_mask (loc, r, mask);
+ if (CHECKING_P)
+ {
+ tree e = cxx_eval_bare_aggregate (ctx, r, vc_prvalue,
+ non_constant_p, overflow_p);
+ gcc_checking_assert (e == r);
+ r = e;
+ }
}
}
diff --git a/gcc/fold-const.cc b/gcc/fold-const.cc
index a02ede79fed..db8f7de5680 100644
--- a/gcc/fold-const.cc
+++ b/gcc/fold-const.cc
@@ -8935,7 +8935,8 @@ native_interpret_aggregate (tree type, const unsigned char *ptr, int off,
return NULL_TREE;
for (tree field = TYPE_FIELDS (type); field; field = DECL_CHAIN (field))
{
- if (TREE_CODE (field) != FIELD_DECL || DECL_PADDING_P (field))
+ if (TREE_CODE (field) != FIELD_DECL || DECL_PADDING_P (field)
+ || integer_zerop (DECL_SIZE (field)))
continue;
tree fld = field;
HOST_WIDE_INT bitoff = 0, pos = 0, sz = 0;
base-commit: caabf0973a4e9a26421c94d540e3e20051e93e77
--
2.39.3
^ permalink raw reply [flat|nested] 3+ messages in thread* Re: [PATCH RFA (fold)] c++: constexpr bit_cast with empty field
2023-07-17 21:19 [PATCH RFA (fold)] c++: constexpr bit_cast with empty field Jason Merrill
@ 2023-07-18 11:31 ` Richard Biener
2023-07-18 16:26 ` Jason Merrill
0 siblings, 1 reply; 3+ messages in thread
From: Richard Biener @ 2023-07-18 11:31 UTC (permalink / raw)
To: Jason Merrill; +Cc: gcc-patches
On Mon, Jul 17, 2023 at 11:20 PM Jason Merrill via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> Tested x86_64-pc-linux-gnu, OK for trunk?
>
> -- 8< --
>
> The change to only cache constexpr calls that are
> reduced_constant_expression_p tripped on bit-cast3.C, which failed that
> predicate due to the presence of an empty field in the result of
> native_interpret_aggregate, which reduced_constant_expression_p rejects to
> avoid confusing output_constructor.
>
> This patch proposes to skip such fields in native_interpret_aggregate, since
> they aren't actually involved in the value representation.
>
> gcc/ChangeLog:
>
> * fold-const.cc (native_interpret_aggregate): Skip empty fields.
>
> gcc/cp/ChangeLog:
>
> * constexpr.cc (cxx_eval_bit_cast): Check that the result of
> native_interpret_aggregate doesn't need more evaluation.
> ---
> gcc/cp/constexpr.cc | 9 +++++++++
> gcc/fold-const.cc | 3 ++-
> 2 files changed, 11 insertions(+), 1 deletion(-)
>
> diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc
> index 9d85c3be5cc..6e8f1c2b61e 100644
> --- a/gcc/cp/constexpr.cc
> +++ b/gcc/cp/constexpr.cc
> @@ -1440,6 +1440,8 @@ enum value_cat {
>
> static tree cxx_eval_constant_expression (const constexpr_ctx *, tree,
> value_cat, bool *, bool *, tree * = NULL);
> +static tree cxx_eval_bare_aggregate (const constexpr_ctx *, tree,
> + value_cat, bool *, bool *);
> static tree cxx_fold_indirect_ref (const constexpr_ctx *, location_t, tree, tree,
> bool * = NULL);
> static tree find_heap_var_refs (tree *, int *, void *);
> @@ -4803,6 +4805,13 @@ cxx_eval_bit_cast (const constexpr_ctx *ctx, tree t, bool *non_constant_p,
> {
> clear_type_padding_in_mask (TREE_TYPE (t), mask);
> clear_uchar_or_std_byte_in_mask (loc, r, mask);
> + if (CHECKING_P)
> + {
> + tree e = cxx_eval_bare_aggregate (ctx, r, vc_prvalue,
> + non_constant_p, overflow_p);
> + gcc_checking_assert (e == r);
> + r = e;
> + }
> }
> }
>
> diff --git a/gcc/fold-const.cc b/gcc/fold-const.cc
> index a02ede79fed..db8f7de5680 100644
> --- a/gcc/fold-const.cc
> +++ b/gcc/fold-const.cc
> @@ -8935,7 +8935,8 @@ native_interpret_aggregate (tree type, const unsigned char *ptr, int off,
> return NULL_TREE;
> for (tree field = TYPE_FIELDS (type); field; field = DECL_CHAIN (field))
> {
> - if (TREE_CODE (field) != FIELD_DECL || DECL_PADDING_P (field))
> + if (TREE_CODE (field) != FIELD_DECL || DECL_PADDING_P (field)
> + || integer_zerop (DECL_SIZE (field)))
The gimplifier uses is_empty_type (TREE_TYPE (field)), wouldn't that be better
for consistency reasons at least?
OK with that change or with integer_zerop if there is a reason to not
use is_empty_type
here.
Thanks,
Richard.
> continue;
> tree fld = field;
> HOST_WIDE_INT bitoff = 0, pos = 0, sz = 0;
>
> base-commit: caabf0973a4e9a26421c94d540e3e20051e93e77
> --
> 2.39.3
>
^ permalink raw reply [flat|nested] 3+ messages in thread* Re: [PATCH RFA (fold)] c++: constexpr bit_cast with empty field
2023-07-18 11:31 ` Richard Biener
@ 2023-07-18 16:26 ` Jason Merrill
0 siblings, 0 replies; 3+ messages in thread
From: Jason Merrill @ 2023-07-18 16:26 UTC (permalink / raw)
To: Richard Biener; +Cc: gcc-patches
On 7/18/23 07:31, Richard Biener wrote:
> On Mon, Jul 17, 2023 at 11:20 PM Jason Merrill via Gcc-patches
> <gcc-patches@gcc.gnu.org> wrote:
>>
>> Tested x86_64-pc-linux-gnu, OK for trunk?
>>
>> -- 8< --
>>
>> The change to only cache constexpr calls that are
>> reduced_constant_expression_p tripped on bit-cast3.C, which failed that
>> predicate due to the presence of an empty field in the result of
>> native_interpret_aggregate, which reduced_constant_expression_p rejects to
>> avoid confusing output_constructor.
>>
>> This patch proposes to skip such fields in native_interpret_aggregate, since
>> they aren't actually involved in the value representation.
>>
>> gcc/ChangeLog:
>>
>> * fold-const.cc (native_interpret_aggregate): Skip empty fields.
>>
>> gcc/cp/ChangeLog:
>>
>> * constexpr.cc (cxx_eval_bit_cast): Check that the result of
>> native_interpret_aggregate doesn't need more evaluation.
>> ---
>> gcc/cp/constexpr.cc | 9 +++++++++
>> gcc/fold-const.cc | 3 ++-
>> 2 files changed, 11 insertions(+), 1 deletion(-)
>>
>> diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc
>> index 9d85c3be5cc..6e8f1c2b61e 100644
>> --- a/gcc/cp/constexpr.cc
>> +++ b/gcc/cp/constexpr.cc
>> @@ -1440,6 +1440,8 @@ enum value_cat {
>>
>> static tree cxx_eval_constant_expression (const constexpr_ctx *, tree,
>> value_cat, bool *, bool *, tree * = NULL);
>> +static tree cxx_eval_bare_aggregate (const constexpr_ctx *, tree,
>> + value_cat, bool *, bool *);
>> static tree cxx_fold_indirect_ref (const constexpr_ctx *, location_t, tree, tree,
>> bool * = NULL);
>> static tree find_heap_var_refs (tree *, int *, void *);
>> @@ -4803,6 +4805,13 @@ cxx_eval_bit_cast (const constexpr_ctx *ctx, tree t, bool *non_constant_p,
>> {
>> clear_type_padding_in_mask (TREE_TYPE (t), mask);
>> clear_uchar_or_std_byte_in_mask (loc, r, mask);
>> + if (CHECKING_P)
>> + {
>> + tree e = cxx_eval_bare_aggregate (ctx, r, vc_prvalue,
>> + non_constant_p, overflow_p);
>> + gcc_checking_assert (e == r);
>> + r = e;
>> + }
>> }
>> }
>>
>> diff --git a/gcc/fold-const.cc b/gcc/fold-const.cc
>> index a02ede79fed..db8f7de5680 100644
>> --- a/gcc/fold-const.cc
>> +++ b/gcc/fold-const.cc
>> @@ -8935,7 +8935,8 @@ native_interpret_aggregate (tree type, const unsigned char *ptr, int off,
>> return NULL_TREE;
>> for (tree field = TYPE_FIELDS (type); field; field = DECL_CHAIN (field))
>> {
>> - if (TREE_CODE (field) != FIELD_DECL || DECL_PADDING_P (field))
>> + if (TREE_CODE (field) != FIELD_DECL || DECL_PADDING_P (field)
>> + || integer_zerop (DECL_SIZE (field)))
>
> The gimplifier uses is_empty_type (TREE_TYPE (field)), wouldn't that be better
> for consistency reasons at least?
Good point, thanks. Pushed with that change.
> OK with that change or with integer_zerop if there is a reason to not
> use is_empty_type
> here.
>
> Thanks,
> Richard.
>
>> continue;
>> tree fld = field;
>> HOST_WIDE_INT bitoff = 0, pos = 0, sz = 0;
>>
>> base-commit: caabf0973a4e9a26421c94d540e3e20051e93e77
>> --
>> 2.39.3
>>
>
^ permalink raw reply [flat|nested] 3+ messages in thread
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2023-07-18 11:31 ` Richard Biener
2023-07-18 16:26 ` Jason Merrill
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