[gcc r10-10683] c-family: Fix up shorten_compare for decimal vs. non-decimal float comparison [PR104510]

[Jakub Jelinek <jakub@gcc.gnu.org>]

https://gcc.gnu.org/g:83aea9cb28f729698a79e4262ef3a43a0fd79d4f

commit r10-10683-g83aea9cb28f729698a79e4262ef3a43a0fd79d4f
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Wed Feb 16 09:25:55 2022 +0100

    c-family: Fix up shorten_compare for decimal vs. non-decimal float comparison [PR104510]
    
    The comment in shorten_compare says:
      /* If either arg is decimal float and the other is float, fail.  */
    but the callers of shorten_compare don't expect anything like failure
    as a possibility from the function, callers require that the function
    promotes the operands to the same type, whether the original selected
    *restype_ptr one or some shortened.
    So, if we choose not to shorten, we should still promote to the original
    *restype_ptr.
    
    2022-02-16  Jakub Jelinek  <jakub@redhat.com>
    
            PR c/104510
            * c-common.c (shorten_compare): Convert original arguments to
            the original *restype_ptr when mixing binary and decimal float.
    
            * gcc.dg/dfp/pr104510.c: New test.
    
    (cherry picked from commit 6e74122f0de6748b3fd0ed9183090cd7c61fb53e)

Diff:
---
 gcc/c-family/c-common.c             |  6 +++++-
 gcc/testsuite/gcc.dg/dfp/pr104510.c | 12 ++++++++++++
 2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/gcc/c-family/c-common.c b/gcc/c-family/c-common.c
index 661a194fc89..ad8bdc34a56 100644
--- a/gcc/c-family/c-common.c
+++ b/gcc/c-family/c-common.c
@@ -2980,7 +2980,11 @@ shorten_compare (location_t loc, tree *op0_ptr, tree *op1_ptr,
   else if (real1 && real2
 	   && (DECIMAL_FLOAT_MODE_P (TYPE_MODE (TREE_TYPE (primop0)))
 	       || DECIMAL_FLOAT_MODE_P (TYPE_MODE (TREE_TYPE (primop1)))))
-    return NULL_TREE;
+    {
+      type = *restype_ptr;
+      primop0 = op0;
+      primop1 = op1;
+    }
 
   else if (real1 && real2
 	   && (TYPE_PRECISION (TREE_TYPE (primop0))
diff --git a/gcc/testsuite/gcc.dg/dfp/pr104510.c b/gcc/testsuite/gcc.dg/dfp/pr104510.c
new file mode 100644
index 00000000000..85f4e9707de
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/dfp/pr104510.c
@@ -0,0 +1,12 @@
+/* PR c/104510 */
+/* { dg-do compile } */
+/* { dg-options "" } */
+
+float f;
+_Decimal64 d;
+
+int
+foo (void)
+{
+  return d > (_Decimal32) (_Decimal64) f;
+}