#2043 C++ fenv.h header broken

[Vadim]

After upgrading to mingw 4.0 (gcc 4.8.1), I can no longer compile LLVM. Here's the error:

In file included from c:/rust/src/llvm/lib/Analysis/ConstantFolding.cpp:33:0:
c:/rust/src/llvm/include/llvm/Support/FEnv.h: In function 'void llvm::sys::llvm_fenv_clearexcept()':
c:/rust/src/llvm/include/llvm/Support/FEnv.h:36:17: error: 'FE_ALL_EXCEPT' was not declared in this scope
feclearexcept(FE_ALL_EXCEPT);
^
c:/rust/src/llvm/include/llvm/Support/FEnv.h:36:30: error: 'feclearexcept' was not declared in this scope
feclearexcept(FE_ALL_EXCEPT);
^
c:/rust/src/llvm/include/llvm/Support/FEnv.h: In function 'bool llvm::sys::llvm_fenv_testexcept()':
c:/rust/src/llvm/include/llvm/Support/FEnv.h:47:20: error: 'FE_ALL_EXCEPT' was not declared in this scope
if (fetestexcept(FE_ALL_EXCEPT & ~FE_INEXACT))
^
c:/rust/src/llvm/include/llvm/Support/FEnv.h:47:37: error: 'FE_INEXACT' was not declared in this scope
if (fetestexcept(FE_ALL_EXCEPT & ~FE_INEXACT))
^
c:/rust/src/llvm/include/llvm/Support/FEnv.h:47:47: error: 'fetestexcept' was not declared in this scope
if (fetestexcept(FE_ALL_EXCEPT & ~FE_INEXACT))

The culprit seems to be that "%mingw%\lib\gcc\mingw32\4.8.1\include\c++\fenv.h" header does not include "%mingw%\include\fenv.h" because _GLIBCXX_HAVE_FENV_H is not defined.
I figure that "_GLIBCXX_HAVE_FENV_H" should have been defined in "bits\c++config.h", but it isn't.

[Earnie Boyd]

I'll take a look at the config.log but the issue becomes one of why the upstream system did not find fenv.h to declare the appropriate HAVE environment macro.

[Keith Marshall]

I'm wondering if this is maybe another search order issue, similar to what we've seen before with float.h; maybe even the float.h issue itself, in another guise?

When Danny Smith built the MinGW releases of GCC, he always arranged for the MinGW' host-specific headers to be searched BEFORE the GCC host-neutral headers; that way MinGW's float.h was included, and it pulled in GCC's with an #include_next. However, that's contrary to GCC's natural way of setting things up. If that search order is reversed, as it naturally is in a GCC build, then MinGW's headers such as float.h never get included, because GCC doesn't extend the #include_next courtesy to the platform headers.

[Thad Guidry]

Defining it at the command line below works around the issue, but Earnie is right, it would be nice for the make files to figure it out for themselves :

make CXXFLAGS=-D_GLIBCXX_HAVE_FENV_H

Also, I did notice an existing comment about Clang build not finding fenv.h as well, and a patch was made in the source. Weird.