c++: Fix up taking address of an immediate function diagnostics [PR102753]

On Wed, Oct 20, 2021 at 07:16:44PM -0400, Jason Merrill wrote:
> or an unevaluated operand, or a subexpression of an immediate invocation.
>
> Hmm...that suggests that in consteval23.C, bar(foo) should also be OK,

The following patch handles that by removing the diagnostics about taking
address of immediate function from cp_build_addr_expr_1, and instead diagnoses
it in cp_fold_r.  To do that with proper locations, the patch attempts to
ensure that ADDR_EXPRs of immediate functions get EXPR_LOCATION set and
adds a PTRMEM_CST_LOCATION for PTRMEM_CSTs.  Also, evaluation of
std::source_location::current() is moved from genericization to cp_fold.

2021-11-26  Jakub Jelinek  <jakub@redhat.com>

	PR c++/102753
	* cp-tree.h (struct ptrmem_cst): Add locus member.
	(PTRMEM_CST_LOCATION): Define.
	* tree.c (make_ptrmem_cst): Set PTRMEM_CST_LOCATION to input_location.
	(cp_expr_location): Return PTRMEM_CST_LOCATION for PTRMEM_CST.
	* typeck.c (build_x_unary_op): Overwrite PTRMEM_CST_LOCATION for
	PTRMEM_CST instead of calling maybe_wrap_with_location.
	(cp_build_addr_expr_1): Don't diagnose taking address of
	immediate functions here.  Instead when taking their address make
	sure the returned ADDR_EXPR has EXPR_LOCATION set.
	(expand_ptrmemfunc_cst): Copy over PTRMEM_CST_LOCATION to ADDR_EXPR's
	EXPR_LOCATION.
	(convert_for_assignment): Use cp_expr_loc_or_input_loc instead of
	EXPR_LOC_OR_LOC.
	* pt.c (tsubst_copy): Use build1_loc instead of build1.  Ensure
	ADDR_EXPR of immediate function has EXPR_LOCATION set.
	* cp-gimplify.c (cp_fold_r): Diagnose taking address of immediate
	functions here.  For consteval if don't walk THEN_CLAUSE.
	(cp_genericize_r): Move evaluation of calls to
	std::source_location::current from here to...
	(cp_fold): ... here.  Don't assert calls to immediate functions must
	be source_location_current_p, instead only constant evaluate
	calls to source_location_current_p.

	* g++.dg/cpp2a/consteval20.C: Add some extra tests.
	* g++.dg/cpp2a/consteval23.C: Likewise.
	* g++.dg/cpp2a/consteval25.C: New test.
	* g++.dg/cpp2a/srcloc20.C: New test.

1 files changed, 64 insertions, 13 deletions

diff --git a/gcc/cp/cp-gimplify.c b/gcc/cp/cp-gimplify.c
index c1691c3..2fbb423 100644
--- a/gcc/cp/cp-gimplify.c
+++ b/gcc/cp/cp-gimplify.c
@@ -900,8 +900,39 @@ struct cp_genericize_data
 static tree
 cp_fold_r (tree *stmt_p, int *walk_subtrees, void *data)
 {
-  tree stmt;
-  enum tree_code code;
+  tree stmt = *stmt_p;
+  enum tree_code code = TREE_CODE (stmt);
+
+  switch (code)
+    {
+    case PTRMEM_CST:
+      if (TREE_CODE (PTRMEM_CST_MEMBER (stmt)) == FUNCTION_DECL
+	  && DECL_IMMEDIATE_FUNCTION_P (PTRMEM_CST_MEMBER (stmt)))
+	{
+	  if (!((hash_set<tree> *) data)->add (stmt))
+	    error_at (PTRMEM_CST_LOCATION (stmt),
+		      "taking address of an immediate function %qD",
+		      PTRMEM_CST_MEMBER (stmt));
+	  stmt = *stmt_p = build_zero_cst (TREE_TYPE (stmt));
+	  break;
+	}
+      break;
+
+    case ADDR_EXPR:
+      if (TREE_CODE (TREE_OPERAND (stmt, 0)) == FUNCTION_DECL
+	  && DECL_IMMEDIATE_FUNCTION_P (TREE_OPERAND (stmt, 0)))
+	{
+	  error_at (EXPR_LOCATION (stmt),
+		    "taking address of an immediate function %qD",
+		    TREE_OPERAND (stmt, 0));
+	  stmt = *stmt_p = build_zero_cst (TREE_TYPE (stmt));
+	  break;
+	}
+      break;
+
+    default:
+      break;
+    }
 
   *stmt_p = stmt = cp_fold (*stmt_p);
 
@@ -917,12 +948,16 @@ cp_fold_r (tree *stmt_p, int *walk_subtrees, void *data)
     }
 
   code = TREE_CODE (stmt);
-  if (code == OMP_FOR || code == OMP_SIMD || code == OMP_DISTRIBUTE
-      || code == OMP_LOOP || code == OMP_TASKLOOP || code == OACC_LOOP)
+  switch (code)
     {
       tree x;
       int i, n;
-
+    case OMP_FOR:
+    case OMP_SIMD:
+    case OMP_DISTRIBUTE:
+    case OMP_LOOP:
+    case OMP_TASKLOOP:
+    case OACC_LOOP:
       cp_walk_tree (&OMP_FOR_BODY (stmt), cp_fold_r, data, NULL);
       cp_walk_tree (&OMP_FOR_CLAUSES (stmt), cp_fold_r, data, NULL);
       cp_walk_tree (&OMP_FOR_INIT (stmt), cp_fold_r, data, NULL);
@@ -961,6 +996,22 @@ cp_fold_r (tree *stmt_p, int *walk_subtrees, void *data)
 	}
       cp_walk_tree (&OMP_FOR_PRE_BODY (stmt), cp_fold_r, data, NULL);
       *walk_subtrees = 0;
+      return NULL;
+
+    case IF_STMT:
+      if (IF_STMT_CONSTEVAL_P (stmt))
+	{
+	  /* Don't walk THEN_CLAUSE (stmt) for consteval if.  IF_COND is always
+	     boolean_false_node.  */
+	  cp_walk_tree (&ELSE_CLAUSE (stmt), cp_fold_r, data, NULL);
+	  cp_walk_tree (&IF_SCOPE (stmt), cp_fold_r, data, NULL);
+	  *walk_subtrees = 0;
+	  return NULL;
+	}
+      break;
+
+    default:
+      break;
     }
 
   return NULL;
@@ -1476,14 +1527,6 @@ cp_genericize_r (tree *stmt_p, int *walk_subtrees, void *data)
 	  break;
 	}
 
-      if (tree fndecl = cp_get_callee_fndecl_nofold (stmt))
-	if (DECL_IMMEDIATE_FUNCTION_P (fndecl))
-	  {
-	    gcc_assert (source_location_current_p (fndecl));
-	    *stmt_p = cxx_constant_value (stmt);
-	    break;
-	  }
-
       if (!wtd->no_sanitize_p
 	  && sanitize_flags_p ((SANITIZE_NULL
 				| SANITIZE_ALIGNMENT | SANITIZE_VPTR)))
@@ -2629,6 +2672,14 @@ cp_fold (tree x)
 	int sv = optimize, nw = sv;
 	tree callee = get_callee_fndecl (x);
 
+	if (tree fndecl = cp_get_callee_fndecl_nofold (x))
+	  if (DECL_IMMEDIATE_FUNCTION_P (fndecl)
+	      && source_location_current_p (fndecl))
+	    {
+	      x = cxx_constant_value (x);
+	      break;
+	    }
+
 	/* Some built-in function calls will be evaluated at compile-time in
 	   fold ().  Set optimize to 1 when folding __builtin_constant_p inside
 	   a constexpr function so that fold_builtin_1 doesn't fold it to 0.  */