[cfe-dev] CLang 2.1 doesn't catch assert within if

Don Quixote de la Mancha quixote at dulcineatech.com
Fri Oct 7 22:02:29 PDT 2011

I've been looking around for an analysis I could add to clang, but I
used Xcode 4.1's clang to test this, which only has CLang 2.1.  Could
someone please check whether the current SVN catches this?  I would
check myself but I am having some trouble getting the current SVN to
build.  It's not the source code but some arcane problems with the
configure shell scripts.  If I can't figure out my configure problem
soon I will ask about it here.

If the current SVN does not catch this, I'd like to do the work to add
the analysis myself.  I've been following the list for a couple weeks
and understand now what would be expected of my code for it to be
accepted.  I will open a Bugzilla bug to track my progress.

You NEVER EVER want to do the following:

if ( condition )
  assert( must_be_true );


If NDEBUG is defined as for a release or profile build, you'll get the
following in your preprocessed code, which will be very hard to debug:

if ( condition )

If you really must insist on putting an assert as the only line within
an if statement, you MUST place it in a Basic Block:

if ( condition ){
  assert( must_be_true );

Even better is to make the if statement part of the assert:

assert( condition && must_be_true );

Back in the day I wrote a new library to replace my client's old one.
To test that my new library got the same results as his old one, he
asked me to link his executable with both his old and my new library,
and to compare the results of all the calls to each library.  I don't
recall why anymore but I actually made the mistake, then spent all day
long tracking down my bug, as the executables and both libraries were
very complex.

I'm running Mac OS X Snow Leopard 10.6.8 on a MacBook Pro, Model
Identifier MacBookPro1,1 (32-bit Core Duo, NOT 64-bit Core 2 Duo).

$ clang --version
Apple clang version 2.1 (tags/Apple/clang-163.7.1) (based on LLVM 3.0svn)
Target: i386-apple-darwin10.8.0
Thread model: posix

$ gcc --version
i686-apple-darwin10-llvm-gcc-4.2 (GCC) 4.2.1 (Based on Apple Inc.
build 5658) (LLVM build 2335.15.00)

$ gcc --pedantic -Wall -c assert_within_if.c

This compile succeeds without any warnings.

$ clang --analyze assert_within_if.c

CLang doesn't print anything to the terminal.  assert_within_if.plist
doesn't contain any diagnostics.

====== Cut Here ======
/* assert_within_if.c */
#include <stdlib.h>
#include <assert.h>

int assert_within_if( int flag, int  *pointer );

int assert_within_if( int flag, int  *pointer )
	int result = 0;

	if ( flag )
		assert( NULL != pointer );

	result = *pointer;

	return result;

====== Cut Here =====

Ever Faithful,

Don Quixote
Don Quixote de la Mancha
Dulcinea Technologies Corporation
Software of Elegance and Beauty
quixote at dulcineatech.com

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