Re: [PATCH RFA (fold)] c++: constexpr bit_cast with empty field

2023-07-18 Thread Jason Merrill via 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
 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

Re: [PATCH RFA (fold)] c++: constexpr bit_cast with empty field

2023-07-18 Thread Richard Biener via Gcc-patches 
On Mon, Jul 17, 2023 at 11:20 PM Jason Merrill via Gcc-patches
 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
>

[PATCH RFA (fold)] c++: constexpr bit_cast with empty field

2023-07-17 Thread Jason Merrill via 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