[PATCH] c++: unifying REAL_CSTs [PR110809]

[Patrick Palka via Gcc-patches]

Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
trunk/13 (after the branch is unfrozen)?

-- >8 --

This teaches unify how to compare two REAL_CSTs.

        PR c++/110809

gcc/cp/ChangeLog:

        * pt.cc (unify) <case INTEGER_CST>: Generalize to handle
        REAL_CST as well.

gcc/testsuite/ChangeLog:

        * g++.dg/cpp2a/nontype-float3.C: New test.
---
 gcc/cp/pt.cc                                |  5 +++--
 gcc/testsuite/g++.dg/cpp2a/nontype-float3.C | 12 ++++++++++++
 2 files changed, 15 insertions(+), 2 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/cpp2a/nontype-float3.C

diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index d342ab5929a..1e09f304490 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -24890,12 +24890,13 @@ unify (tree tparms, tree targs, tree parm, tree arg, 
int strict,
       /* Types INTEGER_CST and MINUS_EXPR can come from array bounds.  */
       /* Type INTEGER_CST can come from ordinary constant template args.  */
     case INTEGER_CST:
+    case REAL_CST:
       while (CONVERT_EXPR_P (arg))
        arg = TREE_OPERAND (arg, 0);
 
-      if (TREE_CODE (arg) != INTEGER_CST)
+      if (TREE_CODE (arg) != TREE_CODE (parm))
        return unify_template_argument_mismatch (explain_p, parm, arg);
-      return (tree_int_cst_equal (parm, arg)
+      return (simple_cst_equal (parm, arg)
              ? unify_success (explain_p)
              : unify_template_argument_mismatch (explain_p, parm, arg));
 
diff --git a/gcc/testsuite/g++.dg/cpp2a/nontype-float3.C 
b/gcc/testsuite/g++.dg/cpp2a/nontype-float3.C
new file mode 100644
index 00000000000..044fb99905a
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/nontype-float3.C
@@ -0,0 +1,12 @@
+// PR c++/110809
+// { dg-do compile { target c++20 } }
+
+template<class, double> struct A { };
+
+template<class T> void f(A<T, 1.0>);
+template<class T> void f(A<T, 2.0>);
+
+int main() {
+  f(A<int, 1.0>{});
+  f(A<int, 1.1>{}); // { dg-error "no match" }
+}
-- 
2.41.0.450.ga80be15292