From 365b1b3592fd222ad0af74071ca4e81cd98b1f71 Mon Sep 17 00:00:00 2001
From: Xiaole He <hexiaole@kylinos.cn>
Date: Sun, 16 Oct 2022 06:47:03 +0000
Subject: [PATCH] abg-reader: optimize if construction

In 'build_enum_type_decl' function of 'src/abg-reader.cc', the
'for loop' walk through all the child nodes of the '<enum-decl>' for
seeking '<underlying-type>' and '<enumerator>':

/* original src/abg-reader.cc begin */
static enum_type_decl_sptr
build_enum_type_decl(read_context& ctxt,
             const xmlNodePtr node,
             bool add_to_current_scope)
{
  ...
  for (xmlNodePtr n = xmlFirstElementChild(node);
       n;
       n = xmlNextElementSibling(n))
    {
      if (xmlStrEqual(n->name, BAD_CAST("underlying-type")))
      {
         ...
      }

      if (xmlStrEqual(n->name, BAD_CAST("enumerator")))
      {
         ...
      }
    }
  ...
}
/* original src/abg-reader.cc end */

Here uses 2 separate 'if' statements for seeking, that is, for any
child node of the '<enum-decl>', there involves 2 'if' comparations.
Because the child node of the '<enum-decl>' is either
'<underlying-type>' or '<enumerator>', there would be a slight
optimization when use 'if-else if' construction instead, like below:

/* optimized src/abg-reader.cc begin */
for (xmlNodePtr n = xmlFirstElementChild(node);
     n;
     n = xmlNextElementSibling(n))
  {
    if (xmlStrEqual(n->name, BAD_CAST("underlying-type")))
    {
       ...
    }
    else if (xmlStrEqual(n->name, BAD_CAST("enumerator")))
    {
       ...
    }
  }
/* optimized src/abg-reader.cc end */

Supposing there has the test case:

/* test case begin */
<abi-instr version='1.0'>
  <enum-decl name='E' filepath='../../abitests/test-enum0-v0.cc' line='1' column='6' id='type-id-2'>
    <underlying-type type-id='type-id-1'/>
    <enumerator name='e0' value='0'/>
    <enumerator name='e2' value='1'/>
  </enum-decl>
</abi-instr>
/* test case end */

When parsing the '<underlying-type>' xml tag, for the original
'src/abg-reader.cc', there involves 2 'if' comparations. But involves
only 1 'if' comparation for the optimized 'src/abg-reader.cc'.

Signed-off-by: Xiaole He <hexiaole@kylinos.cn>
Tested-by: Xiaole He <hexiaole@kylinos.cn>
Signed-off-by: Dodji Seketeli <dodji@redhat.com>
---
 src/abg-reader.cc | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/src/abg-reader.cc b/src/abg-reader.cc
index b55808b9..4afa427a 100644
--- a/src/abg-reader.cc
+++ b/src/abg-reader.cc
@@ -4602,8 +4602,7 @@ build_enum_type_decl(read_context&	ctxt,
 	    base_type_id = CHAR_STR(a);
 	  continue;
 	}
-
-      if (xmlStrEqual(n->name, BAD_CAST("enumerator")))
+      else if (xmlStrEqual(n->name, BAD_CAST("enumerator")))
 	{
 	  string name;
 	  int64_t value = 0;