[gcc(refs/users/marxin/heads/marxin-gcc-benchmark-branch)] c++: Replay errors during diagnosis of constraint satisfaction failures

[gcc(refs/users/marxin/heads/marxin-gcc-benchmark-branch)] c++: Replay errors during diagnosis of constraint satisfaction failures

[Martin Liska]

https://gcc.gnu.org/g:75defde9fb56157d5f0279720d48866925b71b19

commit 75defde9fb56157d5f0279720d48866925b71b19
Author: Patrick Palka <ppalka@redhat.com>
Date:   Sat Mar 28 08:43:20 2020 -0400

    c++: Replay errors during diagnosis of constraint satisfaction failures
    
    This patch adds a new flag -fconcepts-diagnostics-depth to the C++ frontend
    which controls how deeply we replay errors when diagnosing a constraint
    satisfaction failure.  The default is -fconcepts-diagnostics-depth=1 which
    diagnoses only the topmost constraint satisfaction failure and is consistent
    with our behavior before this patch.  By increasing this flag's value, the user
    can control how deeply they want the compiler to explain a constraint
    satisfaction error.
    
    For example, if the unsatisfied constraint is a disjunction, then the default
    behavior is to just say "no branch in the disjunction is satisfied", but with
    -fconcepts-diagnostics-depth=2 we will additionally replay and diagnose the
    error in each branch of the disjunction.  And if the unsatisfied constraint is a
    requires expression, then we will replay the error in the requires expression,
    etc.  This proceeds recursively until there is nothing more to replay or we
    exceeded the maximum depth specified by the flag.
    
    Implementation wise, this patch essentially just uncomments the existing
    commented-out code that performs the error-replaying, and along the way adds
    logic to keep track of and limit the current replay depth.  Besides that, there
    is a new routine collect_operands_of_disjunction which flattens a disjunction
    and collects all of its operands into a vector.
    
    The extra diagnostics enabled by this flag are at times longer than they need to
    be (e.g.  "the operand is_array_v<...> is unsatisfied because \n the expression
    is_array_v<...> [with ...] evaluated to false") and not immediately easy to
    follow (especially when there are nested disjunctions), but the transparency
    provided by these optional diagnostics seems to be pretty helpful in practice.
    
    gcc/c-family/ChangeLog:
    
            * c.opt: Add -fconcepts-diagnostics-depth.
    
    gcc/cp/ChangeLog:
    
            * constraint.cc (finish_constraint_binary_op): Set the location of EXPR
            as well as its range, because build_x_binary_op doesn't always do so.
            (current_constraint_diagnosis_depth): New.
            (concepts_diagnostics_max_depth_exceeded_p): New.
            (collect_operands_of_disjunction): New.
            (satisfy_disjunction): When diagnosing a satisfaction failure, maybe
            replay each branch of the disjunction, subject to the current diagnosis
            depth.
            (diagnose_valid_expression): When diagnosing a satisfaction failure,
            maybe replay the substitution error, subject to the current diagnosis
            recursion.
            (diagnose_valid_type): Likewise.
            (diagnose_nested_requiremnet): Likewise.
            (diagnosing_failed_constraint::diagnosing_failed_constraint): Increment
            current_constraint_diagnosis_depth when diagnosing.
            (diagnosing_failed_constraint::~diagnosing_failed_constraint): Decrement
            current_constraint_diagnosis_depth when diagnosing.
            (diagnosing_failed_constraint::replay_errors_p): New static member
            function.
            (diagnose_constraints): Don't diagnose if concepts_diagnostics_max_depth
            is 0.  Emit a one-off note to increase -fconcepts-diagnostics-depth if
            the limit was exceeded.
            * cp-tree.h (diagnosing_failed_constraint::replay_errors_p): Declare.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/concepts/diagnostic2.C: Expect "no operand" instead of
            "neither operand".
            * g++.dg/concepts/diagnostic5.C: New test.

Diff:
---
 gcc/c-family/ChangeLog                      |   4 +
 gcc/c-family/c.opt                          |   4 +
 gcc/cp/ChangeLog                            |  26 +++++
 gcc/cp/constraint.cc                        | 150 ++++++++++++++++++++++++----
 gcc/cp/cp-tree.h                            |   1 +
 gcc/testsuite/ChangeLog                     |   6 ++
 gcc/testsuite/g++.dg/concepts/diagnostic2.C |   2 +-
 gcc/testsuite/g++.dg/concepts/diagnostic5.C |  46 +++++++++
 8 files changed, 218 insertions(+), 21 deletions(-)

diff --git a/gcc/c-family/ChangeLog b/gcc/c-family/ChangeLog
index 07ff5593991..38406a8c551 100644
--- a/gcc/c-family/ChangeLog
+++ b/gcc/c-family/ChangeLog
@@ -1,3 +1,7 @@
+2020-03-28  Patrick Palka  <ppalka@redhat.com>
+
+	* c.opt: Add -fconcepts-diagnostics-depth.
+
 2020-03-27  Martin Sebor  <msebor@redhat.com>
 
 	PR c++/94346
diff --git a/gcc/c-family/c.opt b/gcc/c-family/c.opt
index a1e0f4cdc3a..c49da99d395 100644
--- a/gcc/c-family/c.opt
+++ b/gcc/c-family/c.opt
@@ -1453,6 +1453,10 @@ fconcepts-ts
 C++ ObjC++ Var(flag_concepts_ts) Init(0)
 Enable certain features present in the Concepts TS.
 
+fconcepts-diagnostics-depth=
+C++ ObjC++ Joined RejectNegative UInteger Var(concepts_diagnostics_max_depth) Init(1)
+Specify maximum error replay depth during recursive diagnosis of a constraint satisfaction failure.
+
 fcond-mismatch
 C ObjC C++ ObjC++
 Allow the arguments of the '?' operator to have different types.
diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index 885f29d8c86..a65ed141478 100644
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,3 +1,29 @@
+2020-03-28  Patrick Palka  <ppalka@redhat.com>
+
+	* constraint.cc (finish_constraint_binary_op): Set the location of EXPR
+	as well as its range, because build_x_binary_op doesn't always do so.
+	(current_constraint_diagnosis_depth): New.
+	(concepts_diagnostics_max_depth_exceeded_p): New.
+	(collect_operands_of_disjunction): New.
+	(satisfy_disjunction): When diagnosing a satisfaction failure, maybe
+	replay each branch of the disjunction, subject to the current diagnosis
+	depth.
+	(diagnose_valid_expression): When diagnosing a satisfaction failure,
+	maybe replay the substitution error, subject to the current diagnosis
+	recursion.
+	(diagnose_valid_type): Likewise.
+	(diagnose_nested_requiremnet): Likewise.
+	(diagnosing_failed_constraint::diagnosing_failed_constraint): Increment
+	current_constraint_diagnosis_depth when diagnosing.
+	(diagnosing_failed_constraint::~diagnosing_failed_constraint): Decrement
+	current_constraint_diagnosis_depth when diagnosing.
+	(diagnosing_failed_constraint::replay_errors_p): New static member
+	function.
+	(diagnose_constraints): Don't diagnose if concepts_diagnostics_max_depth
+	is 0.  Emit a one-off note to increase -fconcepts-diagnostics-depth if
+	the limit was exceeded.
+	* cp-tree.h (diagnosing_failed_constraint::replay_errors_p): Declare.
+
 2020-03-27  Nathan Sidwell  <nathan@acm.org>
 
 	PR c++/84733
diff --git a/gcc/cp/constraint.cc b/gcc/cp/constraint.cc
index a86bcdf603a..76c520318c3 100644
--- a/gcc/cp/constraint.cc
+++ b/gcc/cp/constraint.cc
@@ -162,6 +162,7 @@ finish_constraint_binary_op (location_t loc,
   /* When either operand is dependent, the overload set may be non-empty.  */
   if (expr == error_mark_node)
     return error_mark_node;
+  expr.set_location (loc);
   expr.set_range (lhs.get_start (), rhs.get_finish ());
   return expr;
 }
@@ -2395,6 +2396,49 @@ satisfy_conjunction (tree t, tree args, subst_info info)
   return satisfy_constraint_r (TREE_OPERAND (t, 1), args, info);
 }
 
+/* The current depth at which we're replaying an error during recursive
+   diagnosis of a constraint satisfaction failure.  */
+
+static int current_constraint_diagnosis_depth;
+
+/* Whether CURRENT_CONSTRAINT_DIAGNOSIS_DEPTH has ever exceeded
+   CONCEPTS_DIAGNOSTICS_MAX_DEPTH during recursive diagnosis of a constraint
+   satisfaction error.  */
+
+static bool concepts_diagnostics_max_depth_exceeded_p;
+
+/* Recursive subroutine of collect_operands_of_disjunction.  T is a normalized
+   subexpression of a constraint (composed of CONJ_CONSTRs and DISJ_CONSTRs)
+   and E is the corresponding unnormalized subexpression (composed of
+   TRUTH_ANDIF_EXPRs and TRUTH_ORIF_EXPRs).  */
+
+static void
+collect_operands_of_disjunction_r (tree t, tree e,
+				   auto_vec<tree_pair> *operands)
+{
+  if (TREE_CODE (e) == TRUTH_ORIF_EXPR)
+    {
+      collect_operands_of_disjunction_r (TREE_OPERAND (t, 0),
+					 TREE_OPERAND (e, 0), operands);
+      collect_operands_of_disjunction_r (TREE_OPERAND (t, 1),
+					 TREE_OPERAND (e, 1), operands);
+    }
+  else
+    {
+      tree_pair p = std::make_pair (t, e);
+      operands->safe_push (p);
+    }
+}
+
+/* Recursively collect the normalized and unnormalized operands of the
+   disjunction T and append them to OPERANDS in order.  */
+
+static void
+collect_operands_of_disjunction (tree t, auto_vec<tree_pair> *operands)
+{
+  collect_operands_of_disjunction_r (t, CONSTR_EXPR (t), operands);
+}
+
 /* Compute the satisfaction of a disjunction.  */
 
 static tree
@@ -2412,11 +2456,25 @@ satisfy_disjunction (tree t, tree args, subst_info info)
   tree rhs = satisfy_constraint_r (TREE_OPERAND (t, 1), args, quiet);
   if (rhs != boolean_true_node && info.noisy ())
     {
-      location_t loc = cp_expr_location (CONSTR_EXPR (t));
-      inform (loc, "neither operand of the disjunction is satisfied");
-      /* TODO: Replay the LHS and RHS to find failures in both branches.  */
-      // satisfy_constraint_r (TREE_OPERAND (t, 0), args, info);
-      // satisfy_constraint_r (TREE_OPERAND (t, 1), args, info);
+      cp_expr disj_expr = CONSTR_EXPR (t);
+      inform (disj_expr.get_location (),
+	      "no operand of the disjunction is satisfied");
+      if (diagnosing_failed_constraint::replay_errors_p ())
+	{
+	  /* Replay the error in each branch of the disjunction.  */
+	  auto_vec<tree_pair> operands;
+	  collect_operands_of_disjunction (t, &operands);
+	  for (unsigned i = 0; i < operands.length (); i++)
+	    {
+	      tree norm_op = operands[i].first;
+	      tree op = operands[i].second;
+	      location_t loc = make_location (cp_expr_location (op),
+					      disj_expr.get_start (),
+					      disj_expr.get_finish ());
+	      inform (loc, "the operand %qE is unsatisfied because", op);
+	      satisfy_constraint_r (norm_op, args, info);
+	    }
+	}
     }
   return rhs;
 }
@@ -3182,10 +3240,14 @@ diagnose_valid_expression (tree expr, tree args, tree in_decl)
     return result;
 
   location_t loc = cp_expr_loc_or_input_loc (expr);
-  inform (loc, "the required expression %qE is invalid", expr);
-
-  /* TODO: Replay the substitution to diagnose the error?  */
-  // tsubst_expr (expr, args, tf_error, in_decl, false);
+  if (diagnosing_failed_constraint::replay_errors_p ())
+    {
+      /* Replay the substitution error.  */
+      inform (loc, "the required expression %qE is invalid, because", expr);
+      tsubst_expr (expr, args, tf_error, in_decl, false);
+    }
+  else
+    inform (loc, "the required expression %qE is invalid", expr);
 
   return error_mark_node;
 }
@@ -3198,10 +3260,14 @@ diagnose_valid_type (tree type, tree args, tree in_decl)
     return result;
 
   location_t loc = cp_expr_loc_or_input_loc (type);
-  inform (loc, "the required type %qT is invalid", type);
-
-  /* TODO: Replay the substitution to diagnose the error?  */
-  // tsubst (type, args, tf_error, in_decl);
+  if (diagnosing_failed_constraint::replay_errors_p ())
+    {
+      /* Replay the substitution error.  */
+      inform (loc, "the required type %qT is invalid, because", type);
+      tsubst (type, args, tf_error, in_decl);
+    }
+  else
+    inform (loc, "the required type %qT is invalid", type);
 
   return error_mark_node;
 }
@@ -3280,11 +3346,16 @@ diagnose_nested_requirement (tree req, tree args)
 
   tree expr = TREE_OPERAND (req, 0);
   location_t loc = cp_expr_location (expr);
-  inform (loc, "nested requirement %qE is not satisfied", expr);
+  if (diagnosing_failed_constraint::replay_errors_p ())
+    {
+      /* Replay the substitution error.  */
+      inform (loc, "nested requirement %qE is not satisfied, because", expr);
+      subst_info noisy (tf_warning_or_error, NULL_TREE);
+      satisfy_constraint_expression (expr, args, noisy);
+    }
+  else
+    inform (loc, "nested requirement %qE is not satisfied", expr);
 
-  /* TODO: Replay the substitution to diagnose the error?  */
-  // subst_info noisy (tf_warning_or_error, NULL_TREE);
-  // satisfy_constraint (norm, args, info);
 }
 
 static void
@@ -3385,14 +3456,38 @@ diagnosing_failed_constraint (tree t, tree args, bool diag)
   : diagnosing_error (diag)
 {
   if (diagnosing_error)
-    current_failed_constraint = tree_cons (args, t, current_failed_constraint);
+    {
+      current_failed_constraint
+	= tree_cons (args, t, current_failed_constraint);
+      ++current_constraint_diagnosis_depth;
+    }
 }
 
 diagnosing_failed_constraint::
 ~diagnosing_failed_constraint ()
 {
-  if (diagnosing_error && current_failed_constraint)
-    current_failed_constraint = TREE_CHAIN (current_failed_constraint);
+  if (diagnosing_error)
+    {
+      --current_constraint_diagnosis_depth;
+      if (current_failed_constraint)
+	current_failed_constraint = TREE_CHAIN (current_failed_constraint);
+    }
+
+}
+
+/* Whether we are allowed to replay an error that underlies a constraint failure
+   at the current diagnosis depth.  */
+
+bool
+diagnosing_failed_constraint::replay_errors_p ()
+{
+  if (current_constraint_diagnosis_depth >= concepts_diagnostics_max_depth)
+    {
+      concepts_diagnostics_max_depth_exceeded_p = true;
+      return false;
+    }
+  else
+    return true;
 }
 
 /* Emit diagnostics detailing the failure ARGS to satisfy the constraints
@@ -3403,11 +3498,26 @@ diagnose_constraints (location_t loc, tree t, tree args)
 {
   inform (loc, "constraints not satisfied");
 
+  if (concepts_diagnostics_max_depth == 0)
+    return;
+
   /* Replay satisfaction, but diagnose errors.  */
   if (!args)
     constraint_satisfaction_value (t, tf_warning_or_error);
   else
     constraint_satisfaction_value (t, args, tf_warning_or_error);
+
+  static bool suggested_p;
+  if (concepts_diagnostics_max_depth_exceeded_p
+      && current_constraint_diagnosis_depth == 0
+      && !suggested_p)
+    {
+      inform (UNKNOWN_LOCATION,
+	      "set %qs to at least %d for more detail",
+	      "-fconcepts-diagnostics-depth=",
+	      concepts_diagnostics_max_depth + 1);
+      suggested_p = true;
+    }
 }
 
 #include "gt-cp-constraint.h"
diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index af773458413..63aaf615926 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -7834,6 +7834,7 @@ struct diagnosing_failed_constraint
 {
   diagnosing_failed_constraint (tree, tree, bool);
   ~diagnosing_failed_constraint ();
+  static bool replay_errors_p ();
 
   bool diagnosing_error;
 };
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 6c3cb701626..f60813f1d26 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,9 @@
+2020-03-28  Patrick Palka  <ppalka@redhat.com>
+
+	* g++.dg/concepts/diagnostic2.C: Expect "no operand" instead of
+	"neither operand".
+	* g++.dg/concepts/diagnostic5.C: New test.
+
 2020-03-28  Jakub Jelinek  <jakub@redhat.com>
 
 	PR c/93573
diff --git a/gcc/testsuite/g++.dg/concepts/diagnostic2.C b/gcc/testsuite/g++.dg/concepts/diagnostic2.C
index ce51b71fa8b..47accb8366e 100644
--- a/gcc/testsuite/g++.dg/concepts/diagnostic2.C
+++ b/gcc/testsuite/g++.dg/concepts/diagnostic2.C
@@ -5,7 +5,7 @@ template<typename T>
   inline constexpr bool foo_v = false;
 
 template<typename T>
-  concept foo = foo_v<T> || foo_v<T&>; // { dg-message "neither operand" }
+  concept foo = foo_v<T> || foo_v<T&>; // { dg-message "no operand" }
 /* { dg-begin-multiline-output "" }
    concept foo = foo_v<T> || foo_v<T&>;
                  ~~~~~~~~~^~~~~~~~~~~~
diff --git a/gcc/testsuite/g++.dg/concepts/diagnostic5.C b/gcc/testsuite/g++.dg/concepts/diagnostic5.C
new file mode 100644
index 00000000000..2641dc18423
--- /dev/null
+++ b/gcc/testsuite/g++.dg/concepts/diagnostic5.C
@@ -0,0 +1,46 @@
+// { dg-do compile { target c++2a } }
+// { dg-additional-options "-fconcepts-diagnostics-depth=2" }
+
+template<typename T>
+  concept c1 = requires { typename T::blah; };
+// { dg-message "satisfaction of .c1<T>. .with T = char." "" { target *-*-* } .-1 }
+// { dg-message "satisfaction of .c1<char\\*>." "" { target *-*-* } .-2 }
+// { dg-message ".typename T::blah. is invalid" "" { target *-*-* } .-3 }
+
+template<typename T>
+  concept c2 = requires (T x) { *x; };
+// { dg-message "satisfaction of .c2<T>. .with T = char." "" { target *-*-* } .-1 }
+// { dg-message "in requirements with .char x." "" { target *-*-* } .-2 }
+// { dg-message "required expression .* is invalid" "" { target *-*-* } .-3 }
+
+template<typename T>
+  concept c3 = __is_same(T, const T) || __is_same(T, int);
+// { dg-message "satisfaction of .c3<T>. .with T = char." "" { target *-*-* } .-1 }
+// { dg-message "no operand of the disjunction is satisfied" "" { target *-*-* } .-2 }
+
+template<typename T>
+  concept c4 = requires (T x) { requires c2<const T> || c2<volatile T>; };
+// { dg-message "satisfaction of .c4<T>. .with T = char." "" { target *-*-* } .-1 }
+// { dg-message "nested requirement" "" { target *-*-* } .-2 }
+
+template<typename T>
+  concept c5 = requires (T x) { { &x } -> c1; };
+// { dg-message "satisfaction of .c5<T>. .with T = char." "" { target *-*-* } .-1 }
+// { dg-message "in requirements with .char x." "" { target *-*-* } .-2 }
+// { dg-message "does not satisfy return-type-requirement" "" { target *-*-* } .-3 }
+// { dg-error "deduced expression type does not satisfy" "" { target *-*-* } .-4 }
+
+template<typename T>
+  requires (c1<T> || c2<T>) || (c3<T> || c4<T>) || c5<T> // { dg-message "49: no operand" }
+  // { dg-message ".c1<T>. is unsatisfied because" "" { target *-*-* } .-1 }
+  // { dg-message ".c2<T>. is unsatisfied because" "" { target *-*-* } .-2 }
+  // { dg-message ".c3<T>. is unsatisfied because" "" { target *-*-* } .-3 }
+  // { dg-message ".c4<T>. is unsatisfied because" "" { target *-*-* } .-4 }
+  // { dg-message ".c5<T>. is unsatisfied because" "" { target *-*-* } .-5 }
+  void foo() { }
+
+void
+bar()
+{
+  foo<char>(); // { dg-error "use of" }
+}