Micro-optimize partial_die_info::read

While profiling the DWARF reader, I noticed that
partial_die_info::read creates a vector to store attributes.  However,
the vector is not needed, as this code only processes a single
attribute at a time.

This patch removes the vector.  On my machine, this improves the time
of "./gdb ./gdb" from 2.22 seconds to 1.92 seconds (mean times over 10
runs).

Note that the attribute is initialized by read_attribute, so it does
not need any special initialization.  Avoiding this also improves
performance a bit.

Tested on x86-64 Fedora 30.  I'm checking this in.

gdb/ChangeLog
2020-04-02  Tom Tromey  <tromey@adacore.com>

	* dwarf2/read.c (partial_die_info::read): Do not create a vector
	of attributes.

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index d8019713cdb52026e9d53c8436832b80f6237f00..993a358d34573e513dfe8c934f13d347bebeafc9 100644 (file)
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,8 @@
+2020-04-02  Tom Tromey  <tromey@adacore.com>
+
+       * dwarf2/read.c (partial_die_info::read): Do not create a vector
+       of attributes.
+
 2020-04-02  Andrew Burgess  <andrew.burgess@embecosm.com>
            Bernd Edlinger <bernd.edlinger@hotmail.de>
            Tom Tromey  <tromey@adacore.com>

diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
index f94c66b4f1bc7f0a8563a361139177faa69ac175..0df5676c4d3ab57b97204e6ecd702ad56661210a 100644 (file)
--- a/gdb/dwarf2/read.c
+++ b/gdb/dwarf2/read.c
@@ -17879,18 +17879,17 @@ partial_die_info::read (const struct die_reader_specs *reader,
   int has_high_pc_attr = 0;
   int high_pc_relative = 0;
 
-  std::vector<struct attribute> attr_vec (abbrev.num_attrs);
   for (i = 0; i < abbrev.num_attrs; ++i)
     {
+      attribute attr;
       bool need_reprocess;
-      info_ptr = read_attribute (reader, &attr_vec[i], &abbrev.attrs[i],
+      info_ptr = read_attribute (reader, &attr, &abbrev.attrs[i],
                                 info_ptr, &need_reprocess);
       /* String and address offsets that need to do the reprocessing have
          already been read at this point, so there is no need to wait until
         the loop terminates to do the reprocessing.  */
       if (need_reprocess)
-       read_attribute_reprocess (reader, &attr_vec[i]);
-      attribute &attr = attr_vec[i];
+       read_attribute_reprocess (reader, &attr);
       /* Store the data if it is of an attribute we want to keep in a
          partial symbol table.  */
       switch (attr.name)