C++ PATCH for c++/81525, auto and generic lambda

Submitted by Jason Merrill on Aug. 9, 2017, 7:20 p.m.

Details

Message ID CADzB+2nr6+=CMquWorBBSvYrm5iNDCVeP9u4Xpx7tB+-=tWv3A@mail.gmail.com
State New
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Commit Message

Jason Merrill Aug. 9, 2017, 7:20 p.m.
In this testcase, when building up an extra version of N to refer to
when instantiating the generic lambda, we were mistakenly replacing
the 'auto' with a template argument for the generic lambda.

Tested x86_64-pc-linux-gnu, applying to trunk and 7.
commit e42e1cc162267b85adfb624daf1b96fc2f5a6f5b
Author: Jason Merrill <jason@redhat.com>
Date:   Mon Aug 7 15:05:51 2017 -0400

            PR c++/81525 - wrong constant value with generic lambda
    
            * pt.c (tsubst_decl) [VAR_DECL]: Avoid clobbering auto.
            (tsubst_copy) [VAR_DECL]: Handle auto.

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diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 3d6f4b5..0f899b9 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -12875,7 +12875,15 @@  tsubst_decl (tree t, tree args, tsubst_flags_t complain)
 		&& VAR_HAD_UNKNOWN_BOUND (t)
 		&& type != error_mark_node)
 	      type = strip_array_domain (type);
+	    tree auto_node = type_uses_auto (type);
+	    int len = TREE_VEC_LENGTH (args);
+	    if (auto_node)
+	      /* Mask off any template args past the variable's context so we
+		 don't replace the auto with an unrelated argument.  */
+	      TREE_VEC_LENGTH (args) = TEMPLATE_TYPE_LEVEL (auto_node) - 1;
 	    type = tsubst (type, args, complain, in_decl);
+	    if (auto_node)
+	      TREE_VEC_LENGTH (args) = len;
 	  }
 	if (VAR_P (r))
 	  {
@@ -14656,6 +14664,10 @@  tsubst_copy (tree t, tree args, tsubst_flags_t complain, tree in_decl)
 			DECL_INITIALIZED_BY_CONSTANT_EXPRESSION_P (r)
 			  = TREE_CONSTANT (r) = true;
 		      DECL_INITIAL (r) = init;
+		      if (tree auto_node = type_uses_auto (TREE_TYPE (r)))
+			TREE_TYPE (r)
+			  = do_auto_deduction (TREE_TYPE (r), init, auto_node,
+					       complain, adc_variable_type);
 		    }
 		  gcc_assert (cp_unevaluated_operand || TREE_STATIC (r)
 			      || decl_constant_var_p (r)
diff --git a/gcc/testsuite/g++.dg/cpp1y/lambda-generic-const4.C b/gcc/testsuite/g++.dg/cpp1y/lambda-generic-const4.C
new file mode 100644
index 0000000..52f4373
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1y/lambda-generic-const4.C
@@ -0,0 +1,20 @@ 
+// PR c++/81525
+// { dg-do compile { target c++14 } }
+
+template <int i> struct A {
+  constexpr operator int () const { return i; }
+};
+template <int i> constexpr A<i> a = {};
+
+template <typename F> void foo (F f) {
+  f (A<0>{});
+}
+template <typename T>
+void bar (T) {
+  constexpr auto N = a<1>;
+  auto f = [&] (auto i) {
+    static_assert (static_cast<int>(N) == 1, "");
+  };
+  foo (f);
+}
+int main () { bar (0); }