re PR middle-end/36578 (cast to long double not taken into account when result stored to a double)

	PR middle-end/36578
	* convert.c (convert_to_real): Do not optimize conversions of
	binary arithmetic operations between binary and decimal
	floating-point types.  Consider mode of target type in determining
	decimal type for arithmetic.  Unless
	flag_unsafe_math_optimizations, do not optimize binary conversions
	where this may change rounding behavior.
	* real.c (real_can_shorten_arithmetic): New.
	* real.h (real_can_shorten_arithmetic): Declare.

testsuite:
	* gcc.dg/dfp/convert-bfp-13.c, gcc.dg/dfp/convert-bfp-14.c,
	gcc.dg/dfp/convert-dfp-fold-2.c, gcc.target/i386/pr36578-1.c,
	gcc.target/i386/pr36578-2.c: New tests.

From-SVN: r141432

1 files changed, 29 insertions, 0 deletions

diff --git a/gcc/real.c b/gcc/real.c
index dc6d748..c5a16a8 100644
--- a/gcc/real.c
+++ b/gcc/real.c
@@ -1266,6 +1266,35 @@ exact_real_inverse (enum machine_mode mode, REAL_VALUE_TYPE *r)
   *r = u;
   return true;
 }
+
+/* Return true if arithmetic on values in IMODE that were promoted
+   from values in TMODE is equivalent to direct arithmetic on values
+   in TMODE.  */
+
+bool
+real_can_shorten_arithmetic (enum machine_mode imode, enum machine_mode tmode)
+{
+  const struct real_format *tfmt, *ifmt;
+  tfmt = REAL_MODE_FORMAT (tmode);
+  ifmt = REAL_MODE_FORMAT (imode);
+  /* These conditions are conservative rather than trying to catch the
+     exact boundary conditions; the main case to allow is IEEE float
+     and double.  */
+  return (ifmt->b == tfmt->b
+	  && ifmt->p > 2 * tfmt->p
+	  && ifmt->emin < 2 * tfmt->emin - tfmt->p - 2
+	  && ifmt->emin < tfmt->emin - tfmt->emax - tfmt->p - 2
+	  && ifmt->emax > 2 * tfmt->emax + 2
+	  && ifmt->emax > tfmt->emax - tfmt->emin + tfmt->p + 2
+	  && ifmt->round_towards_zero == tfmt->round_towards_zero
+	  && (ifmt->has_sign_dependent_rounding
+	      == tfmt->has_sign_dependent_rounding)
+	  && ifmt->has_nans >= tfmt->has_nans
+	  && ifmt->has_inf >= tfmt->has_inf
+	  && ifmt->has_signed_zero >= tfmt->has_signed_zero
+	  && !MODE_COMPOSITE_P (tmode)
+	  && !MODE_COMPOSITE_P (imode));
+}
 
 /* Render R as an integer.  */