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Date: Thu, 7 Feb 2013 14:31:07 +0100 (CET)
From: Richard Biener
To: gcc-patches@gcc.gnu.org
Cc: Jakub Jelinek
Subject: [PATCH][www] Add loop case to non-bugs in bugs.html
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As promised, a bugs.html entry.
Ok?
Thanks,
Richard.
2013-02-07 Richard Biener
* bugs/index.html: Add "Loops do not terminate" case to non-bugs.
Index: index.html
===================================================================
RCS file: /cvs/gcc/wwwdocs/htdocs/bugs/index.html,v
retrieving revision 1.109
diff -u -r1.109 index.html
--- index.html 10 Oct 2012 15:52:29 -0000 1.109
+++ index.html 7 Feb 2013 13:29:39 -0000
@@ -429,6 +429,32 @@
article.
+Loops do not terminate
+This is often caused by out-of-bound array accesses or by signed integer
+overflow which both result in undefined behavior according to the ISO
+C standard. For example
+
+
+int
+SATD (int* diff, int use_hadamard)
+{
+ int k, satd = 0, m[16], dd, d[16];
+ ...
+ for (dd=d[k=0]; k<16; dd=d[++k])
+ satd += (dd < 0 ? -dd : dd);
+
+
+accesses d[16]
before the loop is exited with
+the k<16
check. This causes the compiler to
+optimize away the exit test because the new value of k
+must be in the range [0, 15]
according to ISO C.
+
+GCC starting with version 4.8 has a new option
+-fno-aggressive-loop-optimizations
that may help here.
+If it does, then this is a clear sign that your code is not conforming
+to ISO C and it is not a GCC bug.
+
+
Cannot use preprocessor directive in macro arguments.
Let me guess... you used an older version of GCC to compile code
that looks something like this: