Created attachment 471538 [details]
Prevent compiling 3DNOW code in a x86_64 build

Description of problem:

x86_64 builds compile/link code that can not be used.

Version-Release number of selected component (if applicable):

qt-4.7.1-7.fc14

How reproducible:

always

Steps to Reproduce:
1. Build from source RPM on x86_64 system.
2. Note QT_HAVE_3DNOW in build flags
3.
  
Actual results:

Code is compiled which cannot be used by runtime detection of CPU features

Expected results:

Should not build unreachable code

Additional info:

From source file BUILD/qt-everywhere-opensource-src-4.7.1/src/corelib/tools/qsimd.cpp:

#elif defined(__x86_64) || defined(Q_OS_WIN64)
static inline uint detectProcessorFeatures()
{
    uint features = MMX|SSE|SSE2|CMOV;
    uint feature_result = 0;


The base set of CPUs features does not include the 3DNOW instruction set, so that flag won't be set in the "features" variable, so it will never be seen as set at runtime.  Code that does a 'if (features & MMX3DNOW)' will never be reached.