Go patch committed: Traverse expressions with exporting consts

[Ian Lance Taylor <iant@golang.org>]

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This patch to the Go frontend by Julia Lapenko traverses expressions
when exporting constants.  When exporting a constant A that is
expressed through a constant B from another package, it is necessary
to traverse an expression representing the constant A to generate a
sequence of type casts from the constant B.  Before this patch the
frontend didn't collect types of constants contained in such
expressions. This change fetches these types.  This fixes
https://go.dev/issue/51291.  The test case is
https://go.dev/cl/406916.  Bootstrapped and ran Go testsuite on
x86_64-pc-linux-gnu.  Committed to mainline.

Ian

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4105b492d64412b03c3776b49f7663aa094a3f07
diff --git a/gcc/go/gofrontend/MERGE b/gcc/go/gofrontend/MERGE
index 5fa8becde3e..2cf7141c4fa 100644
--- a/gcc/go/gofrontend/MERGE
+++ b/gcc/go/gofrontend/MERGE
@@ -1,4 +1,4 @@
-9d07072e58ca4f9f05343dfd3475b9f49dae5ec5
+0058658a9efb6e5c5faa6f0f65949beea5ddbc98
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.
diff --git a/gcc/go/gofrontend/export.cc b/gcc/go/gofrontend/export.cc
index 70d3f708d32..a30b11af31e 100644
--- a/gcc/go/gofrontend/export.cc
+++ b/gcc/go/gofrontend/export.cc
@@ -124,6 +124,11 @@ class Collect_export_references : public Traverse
   void
   prepare_types(const std::vector<Named_object*>& sorted_exports);
 
+  // Third entry point (called after the method above), to find
+  // all types in expressions referenced by exports.
+  void
+  prepare_expressions(const std::vector<Named_object*>& sorted_exports);
+
  protected:
   // Override of parent class method.
   int
@@ -281,6 +286,28 @@ Collect_export_references::expression(Expression** pexpr)
   return TRAVERSE_CONTINUE;
 }
 
+// Collect up the set of types mentioned in expressions of things we're exporting,
+// and collect all the packages encountered during type traversal, to make sure
+// we can declare things referered to indirectly (for example, in the body of an
+// exported inline function from another package).
+
+void
+Collect_export_references::prepare_expressions(const std::vector<Named_object*>& sorted_exports)
+{
+  for (std::vector<Named_object*>::const_iterator p = sorted_exports.begin();
+       p != sorted_exports.end();
+       ++p)
+    {
+      Named_object* no = *p;
+      if (no->classification() == Named_object::NAMED_OBJECT_CONST)
+        {
+          Expression* e = no->const_value()->expr();
+          if (e != NULL)
+            Expression::traverse(&e, this);
+        }
+    }
+}
+
 // Collect up the set of types mentioned in things we're exporting, and collect
 // all the packages encountered during type traversal, to make sure we can
 // declare things referered to indirectly (for example, in the body of an
@@ -891,6 +918,7 @@ Export::export_globals(const std::string& package_name,
   // Collect up the set of types mentioned in things we're exporting,
   // and any packages that may be referred to indirectly.
   collect.prepare_types(sorted_exports);
+  collect.prepare_expressions(sorted_exports);
 
   // Assign indexes to all exported types and types referenced by
   // things we're exporting.  Return value is index of first non-exported