From: Jason Merrill <jason@redhat.com>
Date: Wed, 19 Mar 2025 09:15:00 +0000 (-0400)
Subject: c++: mangling of array new [PR119316]
X-Git-Tag: basepoints/gcc-16~1101
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=80e1dac3849b134ebd5e0151e9c9e4b8b091de72;p=thirdparty%2Fgcc.git

c++: mangling of array new [PR119316]

Because we build an array type to represent an array new, we hit a VLA
error in compute_array_index_type for a variable length array new.  To avoid
this, let's build the MINUS_EXPR and index type directly.

I also noticed that the non-constant case in write_array_type was assuming
MINUS_EXPR without verifying it, so I added a checking_assert.

I also noticed that Clang doesn't mangle the length of an array new at all,
so I opened https://github.com/itanium-cxx-abi/cxx-abi/issues/199 to clarify
this.

	PR c++/119316

gcc/cp/ChangeLog:

	* mangle.cc (write_expression) [NEW_EXPR]: Avoid using
	compute_array_index_type.
	(write_array_type): Add checking_assert.

gcc/testsuite/ChangeLog:

	* g++.dg/abi/mangle-new1.C: New test.
---

diff --git a/gcc/cp/mangle.cc b/gcc/cp/mangle.cc
index df61f2d573e..9ca5cf6eecd 100644
--- a/gcc/cp/mangle.cc
+++ b/gcc/cp/mangle.cc
@@ -3642,10 +3642,15 @@ write_expression (tree expr)
 
       if (nelts)
 	{
-	  tree domain;
 	  ++processing_template_decl;
-	  domain = compute_array_index_type (NULL_TREE, nelts,
-					     tf_warning_or_error);
+	  /* Avoid compute_array_index_type complaints about
+	     non-constant nelts.  */
+	  tree max = cp_build_binary_op (input_location, MINUS_EXPR,
+					 fold_convert (sizetype, nelts),
+					 size_one_node,
+					 tf_warning_or_error);
+	  max = maybe_constant_value (max);
+	  tree domain = build_index_type (max);
 	  type = build_cplus_array_type (type, domain);
 	  --processing_template_decl;
 	}
@@ -4242,6 +4247,8 @@ write_array_type (const tree type)
 	    }
 	  else
 	    {
+	      gcc_checking_assert (TREE_CODE (max) == MINUS_EXPR
+				   && integer_onep (TREE_OPERAND (max, 1)));
 	      max = TREE_OPERAND (max, 0);
 	      write_expression (max);
 	    }
diff --git a/gcc/testsuite/g++.dg/abi/mangle-new1.C b/gcc/testsuite/g++.dg/abi/mangle-new1.C
new file mode 100644
index 00000000000..bb3ea9b2e96
--- /dev/null
+++ b/gcc/testsuite/g++.dg/abi/mangle-new1.C
@@ -0,0 +1,10 @@
+// PR c++/119316
+// { dg-do compile { target c++11 } }
+
+template <unsigned> struct A { };
+template<typename T>
+auto foo(unsigned n) -> A<sizeof(new T[n])>
+{ return {}; }
+int main() { foo<int>(5); }
+
+// { dg-final { scan-assembler {_Z3fooIiE1AIXszna_Afp__T_EEEj} } }