re PR rtl-optimization/23941 (compress_float_constant creates denormals)

        PR 23941
        * real.c (exact_real_truncate): Return false if the format cannot
        represent the number as a normal.

From-SVN: r104424

1 files changed, 12 insertions, 0 deletions

diff --git a/gcc/real.c b/gcc/real.c
index 2d26185..9b165ec 100644
--- a/gcc/real.c
+++ b/gcc/real.c
@@ -2399,7 +2399,19 @@ real_value_truncate (enum machine_mode mode, REAL_VALUE_TYPE a)
 bool
 exact_real_truncate (enum machine_mode mode, const REAL_VALUE_TYPE *a)
 {
+  const struct real_format *fmt;
   REAL_VALUE_TYPE t;
+  int emin2m1;
+
+  fmt = REAL_MODE_FORMAT (mode);
+  gcc_assert (fmt);
+
+  /* Don't allow conversion to denormals.  */
+  emin2m1 = (fmt->emin - 1) * fmt->log2_b;
+  if (REAL_EXP (a) <= emin2m1)
+    return false;
+
+  /* After conversion to the new mode, the value must be identical.  */
   real_convert (&t, mode, a);
   return real_identical (&t, a);
 }