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

[Jakub Jelinek via Gcc-patches]

Hi!

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.

Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

2022-02-15  Jakub Jelinek  <ja...@redhat.com>

        PR c/104510
        * c-common.cc (shorten_compare): Convert original arguments to
        the original *restype_ptr when mixing binary and decimal float.

        * gcc.dg/dfp/pr104510.c: New test.

--- gcc/c-family/c-common.cc.jj 2022-02-04 14:36:53.998619364 +0100
+++ gcc/c-family/c-common.cc    2022-02-14 19:07:14.305068950 +0100
@@ -3174,7 +3174,11 @@ shorten_compare (location_t loc, tree *o
   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))
--- gcc/testsuite/gcc.dg/dfp/pr104510.c.jj      2022-02-14 19:11:05.610860035 
+0100
+++ gcc/testsuite/gcc.dg/dfp/pr104510.c 2022-02-14 19:10:42.819176224 +0100
@@ -0,0 +1,12 @@
+/* PR c/104510 */
+/* { dg-do compile } */
+/* { dg-options "" } */
+
+float f;
+_Decimal64 d;
+
+int
+foo (void)
+{
+  return d > (_Decimal32) (_Decimal64) f;
+}

        Jakub