c++: simplify build_new_1 when in a template context
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Commit Message
Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look
OK for trunk?
-- >8 --
Since when in a template context we end up just discarding the result
of build_new_1, we don't have to bother with much of the code generation
it performs. This patch makes the function exit early, returning a dummy
non-erroneous result, once we've done pretty much all ahead of time checks
that we could have. In passing avoid building up 'outer_nelts_check' in
a template context too.
gcc/cp/ChangeLog:
* init.cc (build_new_1): Don't build 'outer_nelts_check' when
in a template context. Exit early returning void_node when
in a template context. Simplify the remainder of the function
accordingly.
---
gcc/cp/init.cc | 36 +++++++++++-------------------------
1 file changed, 11 insertions(+), 25 deletions(-)
Comments
On 10/26/23 14:01, Patrick Palka wrote:
> Since when in a template context we end up just discarding the result
> of build_new_1, we don't have to bother with much of the code generation
> it performs. This patch makes the function exit early, returning a dummy
> non-erroneous result, once we've done pretty much all ahead of time checks
> that we could have. In passing avoid building up 'outer_nelts_check' in
> a template context too.
It seems like this stops checking the calls to the constructor and
operator delete?
Jason
On Thu, 26 Oct 2023, Jason Merrill wrote:
> On 10/26/23 14:01, Patrick Palka wrote:
> > Since when in a template context we end up just discarding the result
> > of build_new_1, we don't have to bother with much of the code generation
> > it performs. This patch makes the function exit early, returning a dummy
> > non-erroneous result, once we've done pretty much all ahead of time checks
> > that we could have. In passing avoid building up 'outer_nelts_check' in
> > a template context too.
>
> It seems like this stops checking the calls to the constructor and operator
> delete?
Oops, indeed... I missed that the removed processing_template_decl hunk
still checks the constructor via build_special_member_call. Never mind
then, I guess the function doesn't admit any easy simplification after all :(
I'll add a testcase verifying such ahead of time checking of new-exprs.
>
> Jason
>
>
@@ -3281,7 +3281,7 @@ build_new_1 (vec<tree, va_gc> **placement, tree type, tree nelts,
return error_mark_node;
}
}
- else
+ else if (!processing_template_decl)
{
/* When a runtime check is necessary because the array size
isn't constant, keep only the top-most seven bits (starting
@@ -3467,10 +3467,15 @@ build_new_1 (vec<tree, va_gc> **placement, tree type, tree nelts,
}
}
+ if (processing_template_decl)
+ /* We've done pretty much all we can to check this non-dependent new-expr
+ ahead of time. Any further work is unnecessary since (build_new just
+ discards the result) and/or unsuitable inside a template context. */
+ return void_node;
+
/* If we found a simple case of PLACEMENT_EXPR above, then copy it
into a temporary variable. */
- if (!processing_template_decl
- && TREE_CODE (alloc_call) == CALL_EXPR
+ if (TREE_CODE (alloc_call) == CALL_EXPR
&& call_expr_nargs (alloc_call) == 2
&& TREE_CODE (TREE_TYPE (CALL_EXPR_ARG (alloc_call, 0))) == INTEGER_TYPE
&& TYPE_PTR_P (TREE_TYPE (CALL_EXPR_ARG (alloc_call, 1))))
@@ -3609,25 +3614,7 @@ build_new_1 (vec<tree, va_gc> **placement, tree type, tree nelts,
explicit_value_init_p = true;
}
- if (processing_template_decl)
- {
- /* Avoid an ICE when converting to a base in build_simple_base_path.
- We'll throw this all away anyway, and build_new will create
- a NEW_EXPR. */
- tree t = fold_convert (build_pointer_type (elt_type), data_addr);
- /* build_value_init doesn't work in templates, and we don't need
- the initializer anyway since we're going to throw it away and
- rebuild it at instantiation time, so just build up a single
- constructor call to get any appropriate diagnostics. */
- init_expr = cp_build_fold_indirect_ref (t);
- if (type_build_ctor_call (elt_type))
- init_expr = build_special_member_call (init_expr,
- complete_ctor_identifier,
- init, elt_type,
- LOOKUP_NORMAL,
- complain);
- }
- else if (array_p)
+ if (array_p)
{
tree vecinit = NULL_TREE;
const size_t len = vec_safe_length (*init);
@@ -3721,8 +3708,7 @@ build_new_1 (vec<tree, va_gc> **placement, tree type, tree nelts,
object being initialized, replace them now and don't try to
preevaluate. */
bool had_placeholder = false;
- if (!processing_template_decl
- && TREE_CODE (init_expr) == INIT_EXPR)
+ if (TREE_CODE (init_expr) == INIT_EXPR)
TREE_OPERAND (init_expr, 1)
= replace_placeholders (TREE_OPERAND (init_expr, 1),
TREE_OPERAND (init_expr, 0),
@@ -3760,7 +3746,7 @@ build_new_1 (vec<tree, va_gc> **placement, tree type, tree nelts,
alloc_fn,
complain));
- if (cleanup && init_expr && !processing_template_decl)
+ if (cleanup && init_expr)
/* Ack! First we allocate the memory. Then we set our sentry
variable to true, and expand a cleanup that deletes the
memory if sentry is true. Then we run the constructor, and