[PR debug/77773] segfault when compiling __simd64_float16_t with -g

[Aldy Hernandez]

The following one-liner segfaults on arm-eabi when compiled with 
-mfloat-abi=hard -g:

        __simd64_float16_t usingit;
The problem is that the pretty printer (in simple_type_specificer()) is 
dereferencing a NULL result from c_common_type_for_mode:

          int prec = TYPE_PRECISION (t);
          if (ALL_FIXED_POINT_MODE_P (TYPE_MODE (t)))
            t = c_common_type_for_mode (TYPE_MODE (t), TYPE_SATURATING (t));
          else
            t = c_common_type_for_mode (TYPE_MODE (t), TYPE_UNSIGNED (t));
          if (TYPE_NAME (t))

The type in question is:

        <real_type 0x7fffefdeb150 HF ...>

which corresponds to HFmode and which AFAICT, does not have a type by 
design.

I see that other uses of *type_for_node() throughout the compiler check 
the result for NULL, so perhaps we should do the same here.

The attached patch fixes the problem.

OK for trunk?
commit 10c5a54cb1bf4684864b01cb965d83f3fe474797
Author: Aldy Hernandez <al...@redhat.com>
Date:   Wed Oct 26 12:06:09 2016 -0700

        PR debug/77773
        * c-pretty-print.c (simple_type_specifier): Do not dereference `t'
        if NULL.

diff --git a/gcc/c-family/c-pretty-print.c b/gcc/c-family/c-pretty-print.c
index 90428ca..6bb38a9 100644
--- a/gcc/c-family/c-pretty-print.c
+++ b/gcc/c-family/c-pretty-print.c
@@ -348,7 +348,7 @@ c_pretty_printer::simple_type_specifier (tree t)
            t = c_common_type_for_mode (TYPE_MODE (t), TYPE_SATURATING (t));
          else
            t = c_common_type_for_mode (TYPE_MODE (t), TYPE_UNSIGNED (t));
-         if (TYPE_NAME (t))
+         if (t && TYPE_NAME (t))
            {
              simple_type_specifier (t);
              if (TYPE_PRECISION (t) != prec)
@@ -362,6 +362,7 @@ c_pretty_printer::simple_type_specifier (tree t)
              switch (code)
                {
                case INTEGER_TYPE:
+                 gcc_assert (t != NULL);
                  translate_string (TYPE_UNSIGNED (t)
                                     ? "<unnamed-unsigned:"
                                     : "<unnamed-signed:");