X-Git-Url: http://git.sourceforge.jp/view?a=blobdiff_plain;f=gcc%2FREADME.Portability;h=4101a2f7b4240e998f83f5bd61583b6c92b33cac;hb=cf95b05b99e654234040272fc4095ec0a455d7e0;hp=2724f2a53fd65ccf8db1c04e96b31017b6d36e81;hpb=34c059db3cfd6b16de62f2312f776b74eb459ca5;p=pf3gnuchains%2Fgcc-fork.git

diff --git a/gcc/README.Portability b/gcc/README.Portability
index 2724f2a53fd..4101a2f7b42 100644
--- a/gcc/README.Portability
+++ b/gcc/README.Portability
@@ -10,7 +10,7 @@ This knowledge until know has been sparsely spread around, so I
 thought I'd collect it in one useful place.  Please add and correct
 any problems as you come across them.
 
-I'm going to start from a base of the ISO C89 standard, since that is
+I'm going to start from a base of the ISO C90 standard, since that is
 probably what most people code to naturally.  Obviously using
 constructs introduced after that is not a good idea.
 
@@ -51,14 +51,28 @@ foo (bar, )
 needs to be coded in some other way.
 
 
-free and realloc
-----------------
+Avoid unnecessary test before free
+----------------------------------
 
-Some implementations crash upon attempts to free or realloc the null
-pointer.  Thus if mem might be null, you need to write
+Since SunOS 4 stopped being a reasonable portability target,
+(which happened around 2007) there has been no need to guard
+against "free (NULL)".  Thus, any guard like the following
+constitutes a redundant test:
+
+  if (P)
+    free (P);
+
+It is better to avoid the test.[*]
+Instead, simply free P, regardless of whether it is NULL.
+
+[*] However, if your profiling exposes a test like this in a
+performance-critical loop, say where P is nearly always NULL, and
+the cost of calling free on a NULL pointer would be prohibitively
+high, consider using __builtin_expect, e.g., like this:
+
+  if (__builtin_expect (ptr != NULL, 0))
+    free (ptr);
 
-  if (mem)
-    free (mem);
 
 
 Trigraphs
@@ -194,4 +208,3 @@ o Passing incorrect types to fprintf and friends.
 
 o Adding a function declaration for a module declared in another file to
   a .c file instead of to a .h file.
-