Avoid an allocation in attr_to_dynamic_prop
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Commit Message
I noticed that attr_to_dynamic_prop allocates a dwarf_block, when no
allocation is required. This patch stack-allocates the object
instead.
---
gdb/dwarf2/read.c | 17 ++++++++---------
1 file changed, 8 insertions(+), 9 deletions(-)
Comments
On 2/4/24 20:15, Tom Tromey wrote:
> - struct dwarf_block *block;
> + struct dwarf_block block;
...
> - block = attr->as_block ();
> + block = *attr->as_block ();
I noticed that this replaces a pointer copy with a struct copy. Perhaps
that's not very relevant because the the struct is still small, and the
compiler might optimize the copy away.
But I suppose you could consider doing the micro-optimization of:
...
- struct dwarf_block *block;
+ struct dwarf_block local_block;
+ struct dwarf_block* block = &local_block;
...
and keep the pointer copy.
Anyway, regardless, LGTM.
Reviewed-By: Tom de Vries <tdevries@suse.de>
Thanks,
- Tom
>>>>> "Tom" == Tom de Vries <tdevries@suse.de> writes:
Tom> But I suppose you could consider doing the micro-optimization of:
Tom> ...
Tom> - struct dwarf_block *block;
Tom> + struct dwarf_block local_block;
Tom> + struct dwarf_block* block = &local_block;
Tom> ...
Tom> and keep the pointer copy.
IME these micro-optimizations don't really affect the outcome much. I
tried a bunch like this back in the psymtab days without real effect.
Probably the baton should have a dwarf_block object and then there'd
just be a single copy here.
Tom> Reviewed-By: Tom de Vries <tdevries@suse.de>
Thanks
Tom
@@ -15385,24 +15385,23 @@ attr_to_dynamic_prop (const struct attribute *attr, struct die_info *die,
baton->locexpr.per_cu = cu->per_cu;
baton->locexpr.per_objfile = per_objfile;
- struct dwarf_block *block;
+ struct dwarf_block block;
if (attr->form == DW_FORM_data16)
{
size_t data_size = 16;
- block = XOBNEW (obstack, struct dwarf_block);
- block->size = (data_size
- + 2 /* Extra bytes for DW_OP and arg. */);
- gdb_byte *data = XOBNEWVEC (obstack, gdb_byte, block->size);
+ block.size = (data_size
+ + 2 /* Extra bytes for DW_OP and arg. */);
+ gdb_byte *data = XOBNEWVEC (obstack, gdb_byte, block.size);
data[0] = DW_OP_implicit_value;
data[1] = data_size;
memcpy (&data[2], attr->as_block ()->data, data_size);
- block->data = data;
+ block.data = data;
}
else
- block = attr->as_block ();
+ block = *attr->as_block ();
- baton->locexpr.size = block->size;
- baton->locexpr.data = block->data;
+ baton->locexpr.size = block.size;
+ baton->locexpr.data = block.data;
switch (attr->name)
{
case DW_AT_string_length: