[gcc r12-1792] c++: requires-expression folding [PR101182]

[gcc r12-1792] c++: requires-expression folding [PR101182]

[Patrick Palka]

https://gcc.gnu.org/g:c06493dc30afbf65b14d783c7cd53f20877ef577

commit r12-1792-gc06493dc30afbf65b14d783c7cd53f20877ef577
Author: Patrick Palka <ppalka@redhat.com>
Date:   Thu Jun 24 11:29:02 2021 -0400

    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.

Diff:
---
 gcc/cp/constraint.cc                             |  2 +-
 gcc/cp/cp-gimplify.c                             | 10 ++++------
 gcc/testsuite/g++.dg/cpp2a/concepts-requires25.C | 10 ++++++++++
 3 files changed, 15 insertions(+), 7 deletions(-)

diff --git a/gcc/cp/constraint.cc b/gcc/cp/constraint.cc
index 74b16d27101..286332ba2a7 100644
--- a/gcc/cp/constraint.cc
+++ b/gcc/cp/constraint.cc
@@ -3340,7 +3340,7 @@ 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 96d91b6ef2f..33e10556e32 100644
--- a/gcc/cp/cp-gimplify.c
+++ b/gcc/cp/cp-gimplify.c
@@ -1465,12 +1465,6 @@ 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.  */
@@ -2708,6 +2702,10 @@ 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 00000000000..90cbedb51d4
--- /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++; };
+}