https://community.intel.com/t5/Intel-Fortran-Compiler/Optimization-problem/m-p/745641#M3725 Hi, <BR /><BR />compiling the attached code (&lt;50 lines) with -O0 gives <PRE>ifort -O0 test.f<BR />a.out <INPUT /><BR />d=1.00000000000000<BR /></PRE> while -O1 breaks it and gives different results with each run. <PRE>ifort -O1 test.f<BR />a.out <INPUT /><BR />d= 6.953301764193981E-310<BR />a.out <INPUT /><BR />d= 6.953263450359657E-310<BR /></PRE>The input used is<SPAN><BR /><PRE>cat input<BR /> 1. 0. 0.<BR />-1. 0. 0.<BR /><BR /></PRE> All this is on a Core2Quad, Suse 10.2 (64bit) using ifort Version 10.1 Build 20070913 Package ID: l_fc_p_10.1.008<BR /><BR />I think the code is valid Fortran90. <BR />Any ideas on what might be the problem will be greatly appreciated.<BR /><BR />Thanks<BR />Volker</SPAN> Mon, 26 Nov 2007 12:41:12 GMT v_koch 2007-11-26T12:41:12Z https://community.intel.com/t5/Intel-Fortran-Compiler/Optimization-problem/m-p/745641#M3725 Hi, <BR /><BR />compiling the attached code (&lt;50 lines) with -O0 gives <PRE>ifort -O0 test.f<BR />a.out <INPUT /><BR />d=1.00000000000000<BR /></PRE> while -O1 breaks it and gives different results with each run. <PRE>ifort -O1 test.f<BR />a.out <INPUT /><BR />d= 6.953301764193981E-310<BR />a.out <INPUT /><BR />d= 6.953263450359657E-310<BR /></PRE>The input used is<SPAN><BR /><PRE>cat input<BR /> 1. 0. 0.<BR />-1. 0. 0.<BR /><BR /></PRE> All this is on a Core2Quad, Suse 10.2 (64bit) using ifort Version 10.1 Build 20070913 Package ID: l_fc_p_10.1.008<BR /><BR />I think the code is valid Fortran90. <BR />Any ideas on what might be the problem will be greatly appreciated.<BR /><BR />Thanks<BR />Volker</SPAN> Mon, 26 Nov 2007 12:41:12 GMT https://community.intel.com/t5/Intel-Fortran-Compiler/Optimization-problem/m-p/745641#M3725 v_koch 2007-11-26T12:41:12Z https://community.intel.com/t5/Intel-Fortran-Compiler/Optimization-problem/m-p/745642#M3726 I see, on my SuSE 10.3 32-bit installation, it works again at -O2 (default), but fails, as you said, at -O1. I agree that -O1 is an important option level. I assume this example is cut down from a meaningful case, so you should submit a problem report on premier.intel.com.<BR /> Mon, 26 Nov 2007 15:02:34 GMT https://community.intel.com/t5/Intel-Fortran-Compiler/Optimization-problem/m-p/745642#M3726 TimP 2007-11-26T15:02:34Z