[Bug middle-end/58970] [4.7/4.8/4.9 Regression] internal compiler error: in get_bit_range, at expr.c:4562

[bernd.edlinger at hotmail dot de]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58970

--- Comment #23 from Bernd Edlinger <bernd.edlinger at hotmail dot de> ---
hmm...

all examples I can see, where bitpos is negative,
or less than the representative's bitoffset with offset=NULL,
are just blandtly invalid.

The only valid example would be

struct S { unsigned char s : 1; };
void function(struct S *p)
{
  p[-1].s = 0;
}

However this one is gimplified to

  D.1590 = p + -1;
  D.1590->s = 0;

no ARRAY_REFs at all, never.

Handling all that negative bitoffsets seems to be
a bit too much complication just to generate
valid code for invalid C.

At least returning negative bitoffset could be easily
avoided in get_inner_reference:

--- expr.c.jj    2013-10-31 14:57:05.000000000 +0100
+++ expr.c    2013-11-05 09:24:39.821624212 +0100
@@ -6708,7 +6708,7 @@
       tem = tem.sext (TYPE_PRECISION (sizetype));
       tem = tem.lshift (BITS_PER_UNIT == 8 ? 3 : exact_log2 (BITS_PER_UNIT));
       tem += bit_offset;
-      if (tem.fits_shwi ())
+      if (tem.fits_shwi () && !tem.is_negative ())
     {
       *pbitpos = tem.to_shwi ();
       *poffset = offset = NULL_TREE;