[Bug target/30255] register spills in x87 unit need to be 80-bit, not 64

["whaley at cs dot utsa dot edu" <gcc-bugzilla@gcc.gnu.org>]

------- Comment #3 from whaley at cs dot utsa dot edu  2006-12-18 21:16 -------
BTW, in case it isn't obvious, here's the fix that I typically use for problems
like bug 323 that I cannot when it is gcc itself that is unpredictably spilling
the computation:

void test(double x, double y)
{
  const double y2 = x + 1.0;
  volatile double v[2];
  v[0] = y2;
  v[1] = y;
  if (v[0] != v[1]) printf("error\n");
}

The idea being that the volatile keyword prevents gcc from getting rid of the
store/load cycle, which forces the round-down.  This allows me to still do this
kind of comparison, w/o the speed loss of associated with -ffloat-store (the
compare itself becomes slow due to the store/load, but the body of the code
runs as fast as normal), or the loss of precision associated with always
rounding to 64 bit, as when you change the x87 control word.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30255

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