[gcc(refs/users/rguenth/heads/slp-reorg)] c++: Fix wrong no post-decrement operator error in template [PR94190]

[gcc(refs/users/rguenth/heads/slp-reorg)] c++: Fix wrong no post-decrement operator error in template [PR94190]

[Richard Biener]

https://gcc.gnu.org/g:75b7b7fdc4597170f24c069ea13aa3e14f37fde7

commit 75b7b7fdc4597170f24c069ea13aa3e14f37fde7
Author: Marek Polacek <polacek@redhat.com>
Date:   Mon Mar 16 10:17:11 2020 -0400

    c++: Fix wrong no post-decrement operator error in template [PR94190]
    
    Now that convert_like creates an IMPLICIT_CONV_EXPR when it converts
    something that involves a class in a template, we must be prepared to
    handle it.  In this test, we have a class S and we're converting it
    to long int& using a user-defined conversion since we're performing
    -- on it.  So cp_build_unary_op/POSTDECREMENT_EXPR calls
    build_expr_type_conversion which gets the IMPLICIT_CONV_EXPR.  Before
    the convert_like change it got *S::operator long int &(&b) whose type
    is long int but now it gets IMPLICIT_CONV_EXPR<long int&>(b) whose type
    is a reference type.  But the !MAYBE_CLASS_TYPE_P switch doesn't handle
    reference types and so we complain.
    
    Fixed by calling convert_from_reference on the result of convert_like.
    
            PR c++/94190 - wrong no post-decrement operator error in template.
            * call.c (convert_like_real): Use convert_from_reference on the result.
    
            * g++.dg/conversion/op7.C: New test.

Diff:
---
 gcc/cp/ChangeLog                      |  5 +++++
 gcc/cp/call.c                         |  5 ++++-
 gcc/testsuite/ChangeLog               |  5 +++++
 gcc/testsuite/g++.dg/conversion/op7.C | 22 ++++++++++++++++++++++
 4 files changed, 36 insertions(+), 1 deletion(-)

diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index f867d0e4e1a..4332b07cc5f 100644
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,3 +1,8 @@
+2020-03-24  Marek Polacek  <polacek@redhat.com>
+
+	PR c++/94190 - wrong no post-decrement operator error in template.
+	* call.c (convert_like_real): Use convert_from_reference on the result.
+
 2020-03-24  Jason Merrill  <jason@redhat.com>
 
 	PR c++/94186
diff --git a/gcc/cp/call.c b/gcc/cp/call.c
index 65a3ea35dee..bae4b2c0f52 100644
--- a/gcc/cp/call.c
+++ b/gcc/cp/call.c
@@ -7389,7 +7389,10 @@ convert_like_real (conversion *convs, tree expr, tree fn, int argnum,
   if (processing_template_decl
       && convs->kind != ck_identity
       && (CLASS_TYPE_P (totype) || CLASS_TYPE_P (TREE_TYPE (expr))))
-    return build1 (IMPLICIT_CONV_EXPR, totype, expr);
+    {
+      expr = build1 (IMPLICIT_CONV_EXPR, totype, expr);
+      return convs->kind == ck_ref_bind ? expr : convert_from_reference (expr);
+    }
 
   switch (convs->kind)
     {
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 858ad070d62..bd2e45dcb2d 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2020-03-24  Marek Polacek  <polacek@redhat.com>
+
+	PR c++/94190 - wrong no post-decrement operator error in template.
+	* g++.dg/conversion/op7.C: New test.
+
 2020-03-24  Christophe Lyon  <christophe.lyon@linaro.org>
 
 	* gcc/arm/vfp-1.c: Use arm_fp__ok effective-target.
diff --git a/gcc/testsuite/g++.dg/conversion/op7.C b/gcc/testsuite/g++.dg/conversion/op7.C
new file mode 100644
index 00000000000..c6401d109b4
--- /dev/null
+++ b/gcc/testsuite/g++.dg/conversion/op7.C
@@ -0,0 +1,22 @@
+// PR c++/94190 - wrong no post-decrement operator error in template.
+
+struct S { operator long & (); } b;
+
+template<int> void
+foo ()
+{
+  b--;
+  ++b;
+  --b;
+  b++;
+  !b;
+  ~b;
+  +b;
+  -b;
+}
+
+void
+bar ()
+{
+  foo<0> ();
+}