From: Patrick Palka <ppalka@redhat.com>
Date: Thu, 24 Jun 2021 15:29:02 +0000 (-0400)
Subject: c++: requires-expression folding [PR101182]
X-Git-Tag: releases/gcc-11.2.0~73
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=0f00006c007f3f7e9b6fdd9906ed1e4c791f6b15;p=thirdparty%2Fgcc.git

c++: requires-expression folding [PR101182]

Here we're crashing because cp_fold_function walks into the (templated)
requirements of a requires-expression outside a template, but the
folding routines aren't prepared to handle templated trees.  This patch
fixes this by making cp_fold use evaluate_requires_expr to fold a
requires-expression as a whole, which also means we no longer need to
explicitly do so during gimplification.  (Note that we delay folding
of such requires-expressions for sake of better diagnostics when one is
used as the condition of a failed static_assert.)

	PR c++/101182

gcc/cp/ChangeLog:

	* constraint.cc (evaluate_requires_expr): Adjust function comment.
	* cp-gimplify.c (cp_genericize_r) <case REQUIRES_EXPR>: Move to ...
	(cp_fold) <case REQUIRES_EXPR>: ... here.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp2a/concepts-requires25.C: New test.

(cherry picked from commit c06493dc30afbf65b14d783c7cd53f20877ef577)
---

diff --git a/gcc/cp/constraint.cc b/gcc/cp/constraint.cc
index 6baaa0650b03..3e320afd8409 100644
--- a/gcc/cp/constraint.cc
+++ b/gcc/cp/constraint.cc
@@ -3363,7 +3363,7 @@ evaluate_concept_check (tree check)
 }
 
 /* Evaluate the requires-expression T, returning either boolean_true_node
-   or boolean_false_node.  This is used during gimplification and constexpr
+   or boolean_false_node.  This is used during folding and constexpr
    evaluation.  */
 
 tree
diff --git a/gcc/cp/cp-gimplify.c b/gcc/cp/cp-gimplify.c
index 9079a5b90ca0..f6febaece5ae 100644
--- a/gcc/cp/cp-gimplify.c
+++ b/gcc/cp/cp-gimplify.c
@@ -1459,12 +1459,6 @@ cp_genericize_r (tree *stmt_p, int *walk_subtrees, void *data)
 	TARGET_EXPR_NO_ELIDE (stmt) = 1;
       break;
 
-    case REQUIRES_EXPR:
-      /* Emit the value of the requires-expression.  */
-      *stmt_p = evaluate_requires_expr (stmt);
-      *walk_subtrees = 0;
-      break;
-
     case TEMPLATE_ID_EXPR:
       gcc_assert (concept_check_p (stmt));
       /* Emit the value of the concept check.  */
@@ -2702,6 +2696,10 @@ cp_fold (tree x)
 	x = r;
       break;
 
+    case REQUIRES_EXPR:
+      x = evaluate_requires_expr (x);
+      break;
+
     default:
       return org_x;
     }
diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-requires25.C b/gcc/testsuite/g++.dg/cpp2a/concepts-requires25.C
new file mode 100644
index 000000000000..90cbedb51d41
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-requires25.C
@@ -0,0 +1,10 @@
+// PR c++/101182
+// { dg-do compile { target concepts } }
+
+int a;
+void g(bool);
+
+bool f() {
+  g(requires { a++; });
+  return requires { a++; };
+}