[gcc(refs/vendors/redhat/heads/gcc-8-branch)] dfp: Fix decimal_to_binary [PR94111]

[Jakub Jelinek]

https://gcc.gnu.org/g:c1bc06bd5a2532ee7409fb2ba601c77f6a1ed773

commit c1bc06bd5a2532ee7409fb2ba601c77f6a1ed773
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Wed Mar 11 09:33:52 2020 +0100

    dfp: Fix decimal_to_binary [PR94111]
    
    As e.g. decimal_from_decnumber shows, the REAL_VALUE_TYPE representation
    contains a decimal128 embedded in ->sig only if it is rvc_normal, for
    other kinds like rvc_inf or rvc_nan, ->sig is ignored and everything is
    contained in the REAL_VALUE_TYPE flags (cl, sign, signalling and decimal).
    decimal_to_binary which is used when folding a decimal{32,64,128} constant
    to a binary floating point type ignores this and thus folds infinities and
    NaNs into +0.0.
    The following patch fixes that by only doing that for rvc_normal.
    Similarly to the binary to decimal folding, it goes through a string, in
    order to e.g. deal with canonical NaN mantissas, or binary float formats
    that don't support infinities and/or NaNs.
    
    2020-03-11  Jakub Jelinek  <jakub@redhat.com>
    
            PR middle-end/94111
            * dfp.c (decimal_to_binary): Only use decimal128ToString if from->cl
            is rvc_normal, otherwise use real_to_decimal to print the number to
            string.
    
            * gcc.dg/dfp/pr94111.c: New test.
    
    (cherry picked from commit 343c467ccdc24edb9acd7c60d54914d9656ab499)

Diff:
---
 gcc/dfp.c                          | 10 +++++++---
 gcc/testsuite/gcc.dg/dfp/pr94111.c | 12 ++++++++++++
 2 files changed, 19 insertions(+), 3 deletions(-)

diff --git a/gcc/dfp.c b/gcc/dfp.c
index 230b1b14eaa..26efdc51901 100644
--- a/gcc/dfp.c
+++ b/gcc/dfp.c
@@ -342,9 +342,13 @@ decimal_to_binary (REAL_VALUE_TYPE *to, const REAL_VALUE_TYPE *from,
 		   const real_format *fmt)
 {
   char string[256];
-  const decimal128 *const d128 = (const decimal128 *) from->sig;
-
-  decimal128ToString (d128, string);
+  if (from->cl == rvc_normal)
+    {
+      const decimal128 *const d128 = (const decimal128 *) from->sig;
+      decimal128ToString (d128, string);
+    }
+  else
+    real_to_decimal (string, from, sizeof (string), 0, 1);
   real_from_string3 (to, string, fmt);
 }
 
diff --git a/gcc/testsuite/gcc.dg/dfp/pr94111.c b/gcc/testsuite/gcc.dg/dfp/pr94111.c
new file mode 100644
index 00000000000..ea3a132270a
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/dfp/pr94111.c
@@ -0,0 +1,12 @@
+/* PR middle-end/94111 */
+/* { dg-do run } */
+/* { dg-options "-O2" } */
+
+int
+main ()
+{
+  _Decimal32 d = (_Decimal32) __builtin_inff ();
+  if (!__builtin_isinf ((double) d))
+    __builtin_abort ();
+  return 0;
+}