ping x1

Complex Partial Integers are unimplemented, resulting in an ICE when
attempting to use them. https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79242
This results in GCC7/8 for msp430-elf failing to build.

typedef _Complex __int20 C;

C
foo (C x, C y)
{
  return x + y;
}

(Thanks Jakub - https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79242#c2)

../../gcc/testsuite/gcc.target/msp430/pr79242.c: In function 'foo':
../../gcc/testsuite/gcc.target/msp430/pr79242.c:8:1: internal compiler
error: in make_decl_rtl, at varasm.c:1304
 foo (C x, C y)
 ^~~
0xc07b29 make_decl_rtl(tree_node*)
        ../../gcc/varasm.c:1303
0x67523c set_parm_rtl(tree_node*, rtx_def*)
        ../../gcc/cfgexpand.c:1274
0x79ffb9 expand_function_start(tree_node*)
        ../../gcc/function.c:5166
0x6800e1 execute
        ../../gcc/cfgexpand.c:6250

The attached patch defines a new complex mode for PARTIAL_INT.
You may notice that genmodes.c:complex_class returns MODE_COMPLEX_INT for
MODE_PARTIAL_INT rather than MODE_COMPLEX_PARTIAL_INT. I reviewed the uses of
MODE_COMPLEX_INT and it doesn't looked like a Complex Partial Int requires any
different behaviour to MODE_COMPLEX_INT.

msp430_hard_regno_nregs now returns 2 for CPSImode, but I feel like this may be
better handled in the front-end. PSImode is already defined to only use 1
register, so for a CPSI shouldn't the front-end should be able to work out that
double the amount of registers are required? Thoughts?
Without the definition for CPSI in msp430_hard_regno_nregs,
rtlanal.c:subreg_get_info thinks that a CPSI requires 4 registers of size 2,
instead of 2 registers of size 4.

Successfully bootstrapped and tested for c,c++,fortran,lto,objc on
x86_64-pc-linux-gnu with no regressions on gcc-7-branch.

With this patch gcc-7-branch now builds for msp430-elf. A further bug prevents
trunk from building for msp430-elf.

If the attached patch is acceptable, I would appreciate if someone would commit
it for me (to trunk and gcc-7-branch), as I do not have write access.