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Editorial Team
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Asked: 2026-06-12T15:49:31+00:00

We have a large solution in Visual Studio 2010 which comprises a Fortran exe

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We have a large solution in Visual Studio 2010 which comprises a Fortran exe and multiple Fortran and C++ static library projects:

FORTRAN EXE --> MY_LIB (C++)
--> MY_LIB_2 (C++)
--> MY_LIB_3 (Fortran)

We and have encountered a problem with the run-time performance of the EXE diminishing by about 50% after modifying a C++ static library dependency.

Everything was running fine until we referenced some additional header files in one of the C++ libs. These headers are contained in a project that does not contain any source files, only C++ header files, and therefore does not produce any compiled output of its own:

FORTRAN EXE --> MY_LIB (C++, now includes headers from headers-only project)
--> MY_LIB_2 (C++)
--> MY_LIB_3 (Fortran)

The reason that the headers-only aspect is significant is that it is not possible to set optimizations for a C++ project in Project Properties unless it contains source (.c/.cpp files) and produces some output. However, when included elsewhere, the headers will be subject to the same optimizations as the including project. We’re not doing anything in the code the disables optimizations (e.g. with pragmas).

After the change our code now runs about 50% slower. We are calling only one function in the newly included headers which carries little overhead and does not account for the slowdown. Profiling in AQTime reveals that the slowdown is consistent throughout the code.

What I believe may be causing this is optimizations being inadvertently disabled. At the point the Fortran EXE is linked, we receive a large number of C4748 warnings about optimisations having been disabled in various functions defined in the newly included headers, as well as in and other cpp files that also include them (we didn’t receive these before including the additional headers): 

------ Build started: Project: FortranEXEProject, Configuration: Release Win32 ------
Linking...
   Creating library D:\Source\Release\FortranEXEProject.lib and object D:\Source\Release\FortranEXEProject.exp
Generating code
c:\program files (x86)\microsoft visual studio 10.0\vc\include\memory(620) : warning C4748: /GS can not protect parameters and local variables from local buffer overrun because optimizations are disabled in function
d:\Source\CPPHeaderLibrary\header1.hpp(3231) : warning C4748: /GS can not protect parameters and local variables from local buffer overrun because optimizations are disabled in function
d:\Source\CPPSourceLibrary\source.cpp(54) : warning C4748: /GS can not protect parameters and local variables from local buffer overrun because optimizations are disabled in function

All projects have optimizations enabled and are using link-time code generation (/LTCG).

Process explorer reveals that that the Fortran linker XLink.exe is calling the C++ linker, LINK.exe.

Can anyone explain what is happening here, and how to ensure that optimizations in linked C++ code are maintained in Fortran?

We are using Intel Fortran Composer XE 2011.

Thanks in advance.

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1 Answer

  1. Editorial Team

    In the end we noticed that optimisations had been disabled in a couple of our C++ static library projects further down the call graph which included the new headers. This occurred some time before adding the new headers but clearly the performance hit only came to light when the new code was linked. Turning optimisations back on has fixed the problem; what distracted us was LINK.EXE being invoked by XLINK – it turns out that link.exe is just the windows linker – it is not C++ specific.

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