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x64 code behavior on Win7 & Win8

David_DiLaura1
New Contributor I
‎07-30-2013 11:11 AM
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Colleagues, Steve,

We have an application that is available in both IA-32 and x64 flavors. Engineering code with lots of math so we optimize as much as possible: using /O3 in both IA-32 and x64 compiles. The x64 bit version behaves differently on Win7 than on Win8.  The Win8 results are incorrect. The IA-32 version runs fine in both Win7 and Win8. How differently is the compiler behaving (regarding optimizations, say) when generating x64 code?

David

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Steven_L_Intel1
Employee
‎07-30-2013 12:52 PM
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The compiler generates rather different code, since x64 has a different instruction set as well as more and wider registers. My guess as to the different behavior is probably an uninitialized variable, as otherwise there should not be Win7/Win8 differences.

Do you also use the /Qx or /Qax options to target newer processors? The default is Pentium 4/SSE2.

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