Newlib's trigonometric functions won't compile by Clang

[abrodkin]

Consider a very simple example:

#include <tgmath.h>

float f1, f = 0.5f;

int main(void)
{
        f1 = acos(f);
}

Compile with a full GNU toolchain:

arc-elf32-gcc -c test.c

Compile with a full Clang/LLVM tollchain:

clang -c test.c

Now let's try to compile with Clang and headers of Newlib:

clang -c test.c -I.../newlib/install/arc/include
test.c:8:14: error: '__builtin_choose_expr' requires a constant expression
        f1 = acos(f);
             ^~~~~~~
.../newlib/install/arc/include/tgmath.h:111:20: note: expanded from macro 'acos'
#define acos(__x)               __tg_full(__x, acos)
                                ^~~~~~~~~~~~~~~~~~~~
.../newlib/install/arc/include/tgmath.h:107:2: note: expanded from macro '__tg_full'
        __tg_impl_full(__x, __x, __x, __fn, __fn##f, __fn##l, c##__fn, c##__fn##f, c##__fn##l, __x)
        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
.../newlib/install/arc/include/tgmath.h:96:6: note: expanded from macro '__tg_impl_full'
            __tg_impl_simple(__x, __y, __z, __cfn, __cfnf, __cfnl, __VA_ARGS__),        \
            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
.../newlib/install/arc/include/tgmath.h:86:3: note: expanded from macro '__tg_impl_simple'
                __tg_type_corr(x, y, z, double) || __tg_integer(x, y, z),\
                ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
.../newlib/install/arc/include/tgmath.h:71:2: note: expanded from macro '__tg_type_corr'
        (__tg_type3(__e1, __e2, __e3, __t) ||                           \
        ^
1 error generated.

Any ideas on how to fix that? Is that a problem in Newlib or Clang?

[abrodkin]

Hm, looks like we don't need these headers in Newlib in the first place, as compilers provide its own versions which are known to work for them. See https://github.com/picolibc/picolibc/commit/7c9e9c3480a3e8c8ca1e8e20e4b90f0a38927ea1 & https://github.com/picolibc/picolibc/commit/e6a8fc69964ffba7d48ad8185eb7664f32f4c37b.

[claziss]

Maybe this is an issue which you can discuss it with upstream Newlib maintainers. I see no problem with GNU toolchain.