Re: [PATCH] c++: requires-expression folding [PR101182]

[Jason Merrill via Gcc-patches]

On 6/23/21 7:37 PM, Patrick Palka wrote:

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.  (We don't immediately fold
non-dependent requires-expressions at parse time for sake of better
diagnostics in case one appears as the condition of a failed
static_assert.)

Bootstrapped and regtested on x86_64-pc-linux-gnu, also tested on
cmcstl2 and range-v3, does this look OK for trunk/11?


OK.


PR c++/101182

gcc/cp/ChangeLog:

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

gcc/testsuite/ChangeLog:

* g++.dg/cpp2a/concepts-requires27.C: New test.
---
  gcc/cp/constraint.cc |  2 +-
  gcc/cp/cp-gimplify.c | 10 --
  gcc/testsuite/g++.dg/cpp2a/concepts-requires27.C | 10 ++
  3 files changed, 15 insertions(+), 7 deletions(-)
  create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-requires27.C

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-requires27.C 
b/gcc/testsuite/g++.dg/cpp2a/concepts-requires27.C
new file mode 100644
index 000..87a759a689a
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-requires27.C
@@ -0,0 +1,10 @@
+// PR c++/101182
+// { dg-do compile { target concepts } }
+
+int a;
+int g(bool);
+
+int f() {
+  g(requires { a++; });
+  return requires { a++; };
+}

[PATCH] c++: requires-expression folding [PR101182]

[Patrick Palka via Gcc-patches]

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.  (We don't immediately fold
non-dependent requires-expressions at parse time for sake of better
diagnostics in case one appears as the condition of a failed
static_assert.)

Bootstrapped and regtested on x86_64-pc-linux-gnu, also tested on
cmcstl2 and range-v3, does this look OK for trunk/11?

PR c++/101182

gcc/cp/ChangeLog:

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

gcc/testsuite/ChangeLog:

* g++.dg/cpp2a/concepts-requires27.C: New test.
---
 gcc/cp/constraint.cc |  2 +-
 gcc/cp/cp-gimplify.c | 10 --
 gcc/testsuite/g++.dg/cpp2a/concepts-requires27.C | 10 ++
 3 files changed, 15 insertions(+), 7 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-requires27.C

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-requires27.C 
b/gcc/testsuite/g++.dg/cpp2a/concepts-requires27.C
new file mode 100644
index 000..87a759a689a
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-requires27.C
@@ -0,0 +1,10 @@
+// PR c++/101182
+// { dg-do compile { target concepts } }
+
+int a;
+int g(bool);
+
+int f() {
+  g(requires { a++; });
+  return requires { a++; };
+}
-- 
2.32.0.93.g670b81a890