Go patch committed: In composite literals use temps only for interfaces

[Ian Lance Taylor via Gcc-patches]

This patch to the Go frontend reduces the number of temporaries that
the compiler genrrates for composite literals.  For a composite
literal we only need to introduce a temporary variable if we may be
converting to an interface type, so only do it then.  This saves over
80% of compilation time when using gccgo to compile
cmd/internal/obj/x86, as the GCC middle-end spends a lot of time
pointlessly computing interactions between temporary variables (GCC PR
101064).  This is for that PR and for https://golang.org/issue/46600.
Bootstrapped and ran Go testsuite on x86_64-pc-linux-gnu.  Committed
to mainline and GCC 11 branch.

Ian

98df89168805cd34409307ef0495721d69acef74
diff --git a/gcc/go/gofrontend/MERGE b/gcc/go/gofrontend/MERGE
index f16fb9facc3..f7bcc8c484a 100644
--- a/gcc/go/gofrontend/MERGE
+++ b/gcc/go/gofrontend/MERGE
@@ -1,4 +1,4 @@
-bcafcb3c39530bb325514d6377747eb3127d1a03
+cad187fe3aceb2a7d964b64c70dfa8c8ad24ce65
 
 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/expressions.cc b/gcc/go/gofrontend/expressions.cc
index 5d45e4baab4..94342b2f9b8 100644
--- a/gcc/go/gofrontend/expressions.cc
+++ b/gcc/go/gofrontend/expressions.cc
@@ -15148,7 +15148,7 @@ Struct_construction_expression::do_copy()
 }
 
 // Flatten a struct construction expression.  Store the values into
-// temporaries in case they need interface conversion.
+// temporaries if they may need interface conversion.
 
 Expression*
 Struct_construction_expression::do_flatten(Gogo*, Named_object*,
@@ -15162,10 +15162,13 @@ Struct_construction_expression::do_flatten(Gogo*, 
Named_object*,
     return this;
 
   Location loc = this->location();
+  const Struct_field_list* fields = this->type_->struct_type()->fields();
+  Struct_field_list::const_iterator pf = fields->begin();
   for (Expression_list::iterator pv = this->vals()->begin();
        pv != this->vals()->end();
-       ++pv)
+       ++pv, ++pf)
     {
+      go_assert(pf != fields->end());
       if (*pv != NULL)
        {
           if ((*pv)->is_error_expression() || (*pv)->type()->is_error_type())
@@ -15173,7 +15176,8 @@ Struct_construction_expression::do_flatten(Gogo*, 
Named_object*,
               go_assert(saw_errors());
               return Expression::make_error(loc);
             }
-         if (!(*pv)->is_multi_eval_safe())
+         if (pf->type()->interface_type() != NULL
+             && !(*pv)->is_multi_eval_safe())
            {
              Temporary_statement* temp =
                Statement::make_temporary(NULL, *pv, loc);
@@ -15448,7 +15452,7 @@ Array_construction_expression::do_check_types(Gogo*)
 }
 
 // Flatten an array construction expression.  Store the values into
-// temporaries in case they need interface conversion.
+// temporaries if they may need interface conversion.
 
 Expression*
 Array_construction_expression::do_flatten(Gogo*, Named_object*,
@@ -15467,6 +15471,11 @@ Array_construction_expression::do_flatten(Gogo*, 
Named_object*,
   if (this->is_constant_array() || this->is_static_initializer())
     return this;
 
+  // If the array element type is not an interface type, we don't need
+  // temporaries.
+  if (this->type_->array_type()->element_type()->interface_type() == NULL)
+    return this;
+
   Location loc = this->location();
   for (Expression_list::iterator pv = this->vals()->begin();
        pv != this->vals()->end();