commit c11d9f8275f2bbe9b05cdd815c79ac331f78e15c
author Ian Lance Taylor <iant@golang.org> Fri Aug 20 11:33:29 2021 -0700
committer Ian Lance Taylor <iant@golang.org> Sat Sep 11 21:19:22 2021 +0000
tree f0043e4f18b2a09a1e131cf0516cc46185e9467a
parent 21b30eddc59d92a07264c3b21eb032d6c303d16f

compiler: don't pad zero-sized trailing field in results struct

Nothing can take the address of that field anyhow.

Fixes https://gcc.gnu.org/PR101994

Change-Id: Ie3add79739278ce9d715398f2c4c4dfaef8a293a
Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/343873
Trust: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>

go/types.cc

diff --git a/go/types.cc b/go/types.cc
index e76600d..cd69250 100644
--- a/go/types.cc
+++ b/go/types.cc
@@ -5050,6 +5050,7 @@
 		  Struct_type* st = Type::make_struct_type(sfl,
 							   this->location());
 		  st->set_is_struct_incomparable();
+		  st->set_is_results_struct();
 		  ins.first->second = st->get_backend(gogo);
 		}
 	      bresult_struct = ins.first->second;
@@ -6458,7 +6459,7 @@
         saw_nonzero = true;
     }
   go_assert(i == fields->size());
-  if (saw_nonzero && lastsize == 0)
+  if (saw_nonzero && lastsize == 0 && !type->is_results_struct())
     {
       // For nonzero-sized structs which end in a zero-sized thing, we add
       // an extra byte of padding to the type. This padding ensures that

go/types.h

diff --git a/go/types.h b/go/types.h
index ca1ab49..0c51806 100644
--- a/go/types.h
+++ b/go/types.h
@@ -2501,7 +2501,8 @@
   Struct_type(Struct_field_list* fields, Location location)
     : Type(TYPE_STRUCT),
       fields_(fields), location_(location), all_methods_(NULL),
-      is_struct_incomparable_(false), has_padding_(false)
+      is_struct_incomparable_(false), has_padding_(false),
+      is_results_struct_(false)
   { }
 
   // Return the field NAME.  This only looks at local fields, not at
@@ -2632,6 +2633,17 @@
   set_has_padding()
   { this->has_padding_ = true; }
 
+  // Return whether this is a results struct created to hold the
+  // results of a function that returns multiple results.
+  bool
+  is_results_struct() const
+  { return this->is_results_struct_; }
+
+  // Record that this is a results struct.
+  void
+  set_is_results_struct()
+  { this->is_results_struct_ = true; }
+
   // Write the hash function for this type.
   void
   write_hash_function(Gogo*, Function_type*);
@@ -2742,6 +2754,9 @@
   // True if this struct's backend type has padding, due to trailing
   // zero-sized field.
   bool has_padding_;
+  // True if this is a results struct created to hold the results of a
+  // function that returns multiple results.
+  bool is_results_struct_;
 };
 
 // The type of an array.