gcc/testsuite/gcc.target/spu/dfcgt-nan.c

   1 /* { dg-do compile } */
   2 /* { dg-options "-march=celledp -O1" } */
   3 /* { dg-final { scan-assembler "dfceq" } } */
   4
   5 /* GCC previously transformed an "a <= b" test into "! (a > b)" when
   6    compiling with -march=celledp, so that the dfcgt instruction can be
   7    used to implement the comparison.
   8
   9    However, this transformation violates the IEEE-754 standard in the
  10    presence of NaN values.  If either a or b is a NaN, a <= b should
  11    evaluate to false according to IEEE rules.  However, after the
  12    transformation, a > b as implemented by dfcgt itself returns false,
  13    so the transformed test returns true.
  14
  15    Note that the equivalent transformation is valid for single-
  16    precision floating-point values on the Cell SPU, because the format
  17    does not have NaNs.  It is invalid for double-precision, even on
  18    Cell, however.  */
  19
  20 int test (double a, double b) __attribute__ ((noinline));
  21 int test (double a, double b)
  22 {
  23   return a <= b;
  24 }
  25
  26 int main (void)
  27 {
  28   double x = 0.0;
  29   double y = 0.0/0.0;
  30   return test (x, y);
  31 }