Re: [Mesa-dev] [PATCH] util: Unbreak usage of assert()/debug_assert() inside expressions.

[Jose Fonseca]

On 12/12/14 16:30, Patrick Baggett wrote:


On Fri, Dec 12, 2014 at 10:17 AM, Roland Scheidegger <srol...@vmware.com
<mailto:srol...@vmware.com>> wrote:

    Am 12.12.2014 um 15:09 schrieb Jose Fonseca:
     > From: José Fonseca <jfons...@vmware.com <mailto:jfons...@vmware.com>>
     >
     > f0ba7d897d1c22202531acb70f134f2edc30557d made debug_assert()/assert()
     > unsafe for expressions, but only now with u_atomic.h started to
    rely on
     > them for Windows this became an issue.
     >
     > This fixes non-debug builds with MSVC.
     > ---
     >  src/gallium/auxiliary/util/u_debug.h | 2 +-
     >  1 file changed, 1 insertion(+), 1 deletion(-)
     >
     > diff --git a/src/gallium/auxiliary/util/u_debug.h
    b/src/gallium/auxiliary/util/u_debug.h
     > index badd5e2..4c22fdf 100644
     > --- a/src/gallium/auxiliary/util/u_debug.h
     > +++ b/src/gallium/auxiliary/util/u_debug.h
     > @@ -185,7 +185,7 @@ void _debug_assert_fail(const char *expr,
     >  #ifdef DEBUG
     >  #define debug_assert(expr) ((expr) ? (void)0 :
    _debug_assert_fail(#expr, __FILE__, __LINE__, __FUNCTION__))
     >  #else
     > -#define debug_assert(expr) do { } while (0 && (expr))
     > +#define debug_assert(expr) (void)(0 && (expr))
     >  #endif
     >
     >
     >


Just for my own education, can someone explain what the need for
`debug_assert()` to have any expansion of `expr` at all? Rather, what
breaks with something like:

   #define debug_assert(expr) ((void)0)



Did you read the above mentioned 
f0ba7d897d1c22202531acb70f134f2edc30557d commit message?  It's explained 
there:

$ git show f0ba7d897d1c22202531acb70f134f2edc30557d
commit f0ba7d897d1c22202531acb70f134f2edc30557d
Author: Keith Whitwell <kei...@vmware.com>
Date:   Mon Dec 28 11:05:06 2009 +0000

    util: better fix for unused variable warnings with asserts

    Modify the non-debug (ie disabled) version of assert to expose the
    value in the expression to the compiler (avoiding the unused variable
    messages) while still expanding to a noop.

diff --git a/src/gallium/auxiliary/util/u_debug.h 
b/src/gallium/auxiliary/util/u_debug.h
index abd834c..facc30a 100644
--- a/src/gallium/auxiliary/util/u_debug.h
+++ b/src/gallium/auxiliary/util/u_debug.h
@@ -188,7 +188,7 @@ void _debug_assert_fail(const char *expr,
 #ifdef DEBUG
 #define debug_assert(expr) ((expr) ? (void)0 : 
_debug_assert_fail(#expr, __FILE__, __LINE__, __FUNCTION__))
 #else
-#define debug_assert(expr) ((void)0)
+#define debug_assert(expr) do { } while (0 && (expr))
 #endif



Jose


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