[PATCH] libiberty: d-demangle: use appendc for single chars append

[PATCH] libiberty: d-demangle: use appendc for single chars append

[Luís Ferreira]

[-- Attachment #1: Type: text/plain, Size: 7135 bytes --]

This may be optimized by some modern smart compilers inliner, but since
strlen can be an external source, this can produce unoptimized code.

Signed-off-by: Luís Ferreira <contact@lsferreira.net>
---
 libiberty/d-demangle.c | 60 ++++++++++++++++++++++++------------------
 1 file changed, 34 insertions(+), 26 deletions(-)

diff --git a/libiberty/d-demangle.c b/libiberty/d-demangle.c
index 3adf7b562d1..9b12c8158bb 100644
--- a/libiberty/d-demangle.c
+++ b/libiberty/d-demangle.c
@@ -144,6 +144,14 @@ string_appendn (string *p, const char *s, size_t
n)
     }
 }
 
+static void
+string_appendc (string *p, char c)
+{
+  string_need (p, 1);
+  *p->p = c;
+  p->p++;
+}
+
 static void
 string_prependn (string *p, const char *s, size_t n)
 {
@@ -664,7 +672,7 @@ dlang_function_type (string *decl, const char
*mangled, struct dlang_info *info)
   /* Append to decl in order. */
   string_appendn (decl, type.b, string_length (&type));
   string_appendn (decl, args.b, string_length (&args));
-  string_append (decl, " ");
+  string_appendc (decl, ' ');
   string_appendn (decl, attr.b, string_length (&attr));
 
   string_delete (&attr);
@@ -816,9 +824,9 @@ dlang_type (string *decl, const char *mangled,
struct dlang_info *info)
 	  mangled++;
 	}
       mangled = dlang_type (decl, mangled, info);
-      string_append (decl, "[");
+      string_appendc (decl, '[');
       string_appendn (decl, numptr, num);
-      string_append (decl, "]");
+      string_appendc (decl, ']');
       return mangled;
     }
     case 'H': /* associative array (T[T]) */
@@ -832,9 +840,9 @@ dlang_type (string *decl, const char *mangled,
struct dlang_info *info)
       sztype = string_length (&type);
 
       mangled = dlang_type (decl, mangled, info);
-      string_append (decl, "[");
+      string_appendc (decl, '[');
       string_appendn (decl, type.b, sztype);
-      string_append (decl, "]");
+      string_appendc (decl, ']');
 
       string_delete (&type);
       return mangled;
@@ -844,7 +852,7 @@ dlang_type (string *decl, const char *mangled,
struct dlang_info *info)
       if (!dlang_call_convention_p (mangled))
 	{
 	  mangled = dlang_type (decl, mangled, info);
-	  string_append (decl, "*");
+	  string_appendc (decl, '*');
 	  return mangled;
 	}
       /* Fall through */
@@ -1181,7 +1189,7 @@ dlang_parse_integer (string *decl, const char
*mangled, char type)
 	{
 	  /* Represent as a character literal.  */
 	  char c = (char) val;
-	  string_appendn (decl, &c, 1);
+	  string_appendc (decl, c);
 	}
       else
 	{
@@ -1297,7 +1305,7 @@ dlang_parse_real (string *decl, const char
*mangled)
   /* Hexadecimal prefix and leading bit.  */
   if (*mangled == 'N')
     {
-      string_append (decl, "-");
+      string_appendc (decl, '-');
       mangled++;
     }
 
@@ -1305,14 +1313,14 @@ dlang_parse_real (string *decl, const char
*mangled)
     return NULL;
 
   string_append (decl, "0x");
-  string_appendn (decl, mangled, 1);
-  string_append (decl, ".");
+  string_appendc (decl, *mangled);
+  string_appendc (decl, '.');
   mangled++;
 
   /* Significand.  */
   while (ISXDIGIT (*mangled))
     {
-      string_appendn (decl, mangled, 1);
+      string_appendc (decl, *mangled);
       mangled++;
     }
 
@@ -1325,7 +1333,7 @@ dlang_parse_real (string *decl, const char
*mangled)
 
   if (*mangled == 'N')
     {
-      string_append (decl, "-");
+      string_appendc (decl, '-');
       mangled++;
     }
 
@@ -1352,7 +1360,7 @@ dlang_parse_string (string *decl, const char
*mangled)
     return NULL;
 
   mangled++;
-  string_append (decl, "\"");
+  string_appendc (decl, '\"');
   while (len--)
     {
       char val;
@@ -1365,7 +1373,7 @@ dlang_parse_string (string *decl, const char
*mangled)
       switch (val)
 	{
 	case ' ':
-	  string_append (decl, " ");
+	  string_appendc (decl, ' ');
 	  break;
 	case '\t':
 	  string_append (decl, "\\t");
@@ -1415,7 +1423,7 @@ dlang_parse_arrayliteral (string *decl, const
char *mangled,
   if (mangled == NULL)
     return NULL;
 
-  string_append (decl, "[");
+  string_appendc (decl, '[');
   while (elements--)
     {
       mangled = dlang_value (decl, mangled, NULL, '\0', info);
@@ -1426,7 +1434,7 @@ dlang_parse_arrayliteral (string *decl, const
char *mangled,
 	string_append (decl, ", ");
     }
 
-  string_append (decl, "]");
+  string_appendc (decl, ']');
   return mangled;
 }
 
@@ -1442,14 +1450,14 @@ dlang_parse_assocarray (string *decl, const
char *mangled,
   if (mangled == NULL)
     return NULL;
 
-  string_append (decl, "[");
+  string_appendc (decl, '[');
   while (elements--)
     {
       mangled = dlang_value (decl, mangled, NULL, '\0', info);
       if (mangled == NULL)
 	return NULL;
 
-      string_append (decl, ":");
+      string_appendc (decl, ':');
       mangled = dlang_value (decl, mangled, NULL, '\0', info);
       if (mangled == NULL)
 	return NULL;
@@ -1458,7 +1466,7 @@ dlang_parse_assocarray (string *decl, const char
*mangled,
 	string_append (decl, ", ");
     }
 
-  string_append (decl, "]");
+  string_appendc (decl, ']');
   return mangled;
 }
 
@@ -1477,7 +1485,7 @@ dlang_parse_structlit (string *decl, const char
*mangled, const char *name,
   if (name != NULL)
     string_append (decl, name);
 
-  string_append (decl, "(");
+  string_appendc (decl, '(');
   while (args--)
     {
       mangled = dlang_value (decl, mangled, NULL, '\0', info);
@@ -1488,7 +1496,7 @@ dlang_parse_structlit (string *decl, const char
*mangled, const char *name,
 	string_append (decl, ", ");
     }
 
-  string_append (decl, ")");
+  string_appendc (decl, ')');
   return mangled;
 }
 
@@ -1512,7 +1520,7 @@ dlang_value (string *decl, const char *mangled,
const char *name, char type,
       /* Integral values.  */
     case 'N':
       mangled++;
-      string_append (decl, "-");
+      string_appendc (decl, '-');
       mangled = dlang_parse_integer (decl, mangled, type);
       break;
 
@@ -1538,12 +1546,12 @@ dlang_value (string *decl, const char *mangled,
const char *name, char type,
     case 'c':
       mangled++;
       mangled = dlang_parse_real (decl, mangled);
-      string_append (decl, "+");
+      string_appendc (decl, '+');
       if (mangled == NULL || *mangled != 'c')
 	return NULL;
       mangled++;
       mangled = dlang_parse_real (decl, mangled);
-      string_append (decl, "i");
+      string_appendc (decl, 'i');
       break;
 
       /* String values.  */
@@ -1651,7 +1659,7 @@ dlang_parse_qualified (string *decl, const char
*mangled,
   do
     {
       if (n++)
-	string_append (decl, ".");
+	string_appendc (decl, '.');
 
       /* Skip over anonymous symbols.  */
       while (*mangled == '0')
@@ -1723,7 +1731,7 @@ dlang_parse_tuple (string *decl, const char
*mangled, struct dlang_info *info)
 	string_append (decl, ", ");
     }
 
-  string_append (decl, ")");
+  string_appendc (decl, ')');
   return mangled;
 }
 


[-- Attachment #2: This is a digitally signed message part --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

Re: [PATCH] libiberty: d-demangle: use appendc for single chars append

[Jeff Law]

On 9/29/2021 9:32 AM, Luís Ferreira wrote:
> This may be optimized by some modern smart compilers inliner, but since
> strlen can be an external source, this can produce unoptimized code.
strlen has very well defined semantics by ISO and even if it's defined 
externally compilers know those semantics and can optimize 
appropriately.  In fact, if you build a testcase, compile it with a 
modern compiler, you should see the call to strlen optimized away & the 
call to memcpy turned into a simple store.

So I just don't see the value in adding more code here when we can just 
let the optimizer do its job and get the same result.

I won't object if Iain wants to go forward with this patch, but I'm not 
going forward with it independently.

jeff