[PATCH RFA(tree)] c++: source position of lambda captures [PR84471]

[Jason Merrill <jason@redhat.com>]

Tested x86_64-pc-linux-gnu, OK for trunk?

-- 8< --

If the DECL_VALUE_EXPR of a VAR_DECL has EXPR_LOCATION set, then any use of
that variable looks like it has that location, which leads to the debugger
jumping back and forth for both lambdas and structured bindings.

Rather than fix all the uses, it seems simplest to remove any EXPR_LOCATION
when setting DECL_VALUE_EXPR.  So the cp/ hunks aren't necessary, but it
seems cleaner not to work to add a location that will immediately get
stripped.

	PR c++/84471
	PR c++/107504

gcc/cp/ChangeLog:

	* coroutines.cc (transform_local_var_uses): Don't
	specify a location for DECL_VALUE_EXPR.
	* decl.cc (cp_finish_decomp): Likewise.

gcc/ChangeLog:

	* tree.cc (decl_value_expr_insert): Clear EXPR_LOCATION.

gcc/testsuite/ChangeLog:

	* g++.dg/tree-ssa/value-expr1.C: New test.
	* g++.dg/tree-ssa/value-expr2.C: New test.
	* g++.dg/analyzer/pr93212.C: Move warning.
---
 gcc/cp/coroutines.cc                        |  4 ++--
 gcc/cp/decl.cc                              | 12 +++-------
 gcc/testsuite/g++.dg/analyzer/pr93212.C     |  4 ++--
 gcc/testsuite/g++.dg/tree-ssa/value-expr1.C | 16 +++++++++++++
 gcc/testsuite/g++.dg/tree-ssa/value-expr2.C | 26 +++++++++++++++++++++
 gcc/tree.cc                                 |  3 +++
 6 files changed, 52 insertions(+), 13 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/tree-ssa/value-expr1.C
 create mode 100644 gcc/testsuite/g++.dg/tree-ssa/value-expr2.C

diff --git a/gcc/cp/coroutines.cc b/gcc/cp/coroutines.cc
index 01a3e831ee5..a72bd6bbef0 100644
--- a/gcc/cp/coroutines.cc
+++ b/gcc/cp/coroutines.cc
@@ -2047,8 +2047,8 @@ transform_local_var_uses (tree *stmt, int *do_subtree, void *d)
 	    = lookup_member (lvd->coro_frame_type, local_var.field_id,
 			     /*protect=*/1, /*want_type=*/0,
 			     tf_warning_or_error);
-	  tree fld_idx = build3_loc (lvd->loc, COMPONENT_REF, TREE_TYPE (lvar),
-				     lvd->actor_frame, fld_ref, NULL_TREE);
+	  tree fld_idx = build3 (COMPONENT_REF, TREE_TYPE (lvar),
+				 lvd->actor_frame, fld_ref, NULL_TREE);
 	  local_var.field_idx = fld_idx;
 	  SET_DECL_VALUE_EXPR (lvar, fld_idx);
 	  DECL_HAS_VALUE_EXPR_P (lvar) = true;
diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
index 7af0b05d5f8..59e21581503 100644
--- a/gcc/cp/decl.cc
+++ b/gcc/cp/decl.cc
@@ -9133,9 +9133,7 @@ cp_finish_decomp (tree decl, tree first, unsigned int count)
 	  if (processing_template_decl)
 	    continue;
 	  tree t = unshare_expr (dexp);
-	  t = build4_loc (DECL_SOURCE_LOCATION (v[i]), ARRAY_REF,
-			  eltype, t, size_int (i), NULL_TREE,
-			  NULL_TREE);
+	  t = build4 (ARRAY_REF, eltype, t, size_int (i), NULL_TREE, NULL_TREE);
 	  SET_DECL_VALUE_EXPR (v[i], t);
 	  DECL_HAS_VALUE_EXPR_P (v[i]) = 1;
 	}
@@ -9154,9 +9152,7 @@ cp_finish_decomp (tree decl, tree first, unsigned int count)
 	  if (processing_template_decl)
 	    continue;
 	  tree t = unshare_expr (dexp);
-	  t = build1_loc (DECL_SOURCE_LOCATION (v[i]),
-			  i ? IMAGPART_EXPR : REALPART_EXPR, eltype,
-			  t);
+	  t = build1 (i ? IMAGPART_EXPR : REALPART_EXPR, eltype, t);
 	  SET_DECL_VALUE_EXPR (v[i], t);
 	  DECL_HAS_VALUE_EXPR_P (v[i]) = 1;
 	}
@@ -9180,9 +9176,7 @@ cp_finish_decomp (tree decl, tree first, unsigned int count)
 	  tree t = unshare_expr (dexp);
 	  convert_vector_to_array_for_subscript (DECL_SOURCE_LOCATION (v[i]),
 						 &t, size_int (i));
-	  t = build4_loc (DECL_SOURCE_LOCATION (v[i]), ARRAY_REF,
-			  eltype, t, size_int (i), NULL_TREE,
-			  NULL_TREE);
+	  t = build4 (ARRAY_REF, eltype, t, size_int (i), NULL_TREE, NULL_TREE);
 	  SET_DECL_VALUE_EXPR (v[i], t);
 	  DECL_HAS_VALUE_EXPR_P (v[i]) = 1;
 	}
diff --git a/gcc/testsuite/g++.dg/analyzer/pr93212.C b/gcc/testsuite/g++.dg/analyzer/pr93212.C
index 41507e2b837..1029e8d547b 100644
--- a/gcc/testsuite/g++.dg/analyzer/pr93212.C
+++ b/gcc/testsuite/g++.dg/analyzer/pr93212.C
@@ -4,8 +4,8 @@
 auto lol()
 {
     int aha = 3;
-    return [&aha] { // { dg-warning "dereferencing pointer '.*' to within stale stack frame" }
-        return aha;
+    return [&aha] {
+        return aha; // { dg-warning "dereferencing pointer '.*' to within stale stack frame" }
     };
     /* TODO: may be worth special-casing the reporting of dangling
        references from lambdas, to highlight the declaration, and maybe fix
diff --git a/gcc/testsuite/g++.dg/tree-ssa/value-expr1.C b/gcc/testsuite/g++.dg/tree-ssa/value-expr1.C
new file mode 100644
index 00000000000..946ccc3bd97
--- /dev/null
+++ b/gcc/testsuite/g++.dg/tree-ssa/value-expr1.C
@@ -0,0 +1,16 @@
+// PR c++/84471
+// { dg-do compile { target c++11 } }
+// { dg-additional-options -fdump-tree-gimple-lineno }
+// { dg-final { scan-tree-dump-not {value-expr: \[} "gimple" } }
+
+int main(int argc, char**)
+{
+  int x = 1;
+  auto f = [&x, &argc](const char* i) {
+    i += x;
+    i -= argc;
+    i += argc - x;
+    return i;
+  };
+  f("          ");
+}
diff --git a/gcc/testsuite/g++.dg/tree-ssa/value-expr2.C b/gcc/testsuite/g++.dg/tree-ssa/value-expr2.C
new file mode 100644
index 00000000000..4d00498f214
--- /dev/null
+++ b/gcc/testsuite/g++.dg/tree-ssa/value-expr2.C
@@ -0,0 +1,26 @@
+// PR c++/107504
+// { dg-do compile { target c++17 } }
+// { dg-additional-options -fdump-tree-gimple-lineno }
+// { dg-final { scan-tree-dump-not {value-expr: \[} "gimple" } }
+
+struct S
+{
+  void* i;
+  int j;
+};
+
+S f(char* p)
+{
+  return {p, 1};
+}
+
+int main()
+{
+  char buf[1];
+  auto [x, y] = f(buf);
+  if (x != buf)
+    throw 1;
+  if (y != 1)
+    throw 2;
+  return 0;
+}
diff --git a/gcc/tree.cc b/gcc/tree.cc
index 254b2373dcf..836c51cd4d5 100644
--- a/gcc/tree.cc
+++ b/gcc/tree.cc
@@ -5862,6 +5862,9 @@ decl_value_expr_insert (tree from, tree to)
 {
   struct tree_decl_map *h;
 
+  /* Uses of FROM shouldn't look like they happen at the location of TO.  */
+  protected_set_expr_location (to, UNKNOWN_LOCATION);
+
   h = ggc_alloc<tree_decl_map> ();
   h->base.from = from;
   h->to = to;

base-commit: 70596a0fb2a2ec072e1e97e37616e05041dfa4e5
-- 
2.31.1