commit cad187fe3aceb2a7d964b64c70dfa8c8ad24ce65
author Ian Lance Taylor <iant@golang.org> Mon Jun 28 16:47:55 2021 -0700
committer Ian Lance Taylor <iant@golang.org> Tue Jun 29 17:59:30 2021 +0000
tree f76f0d90bb375113db08f4eb546943cabbb14e01
parent bcafcb3c39530bb325514d6377747eb3127d1a03

compiler: in composite literals use temps only for interfaces

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.

For golang/go#46600

Change-Id: I6f01a3c84762b9d06268c5304af6ffce14a0a031
Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/331513
Trust: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Than McIntosh <thanm@google.com>

go/expressions.cc

diff --git a/go/expressions.cc b/go/expressions.cc
index 5d45e4b..94342b2 100644
--- a/go/expressions.cc
+++ b/go/expressions.cc
@@ -15148,7 +15148,7 @@
 }
 
 // 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 @@
     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 @@
               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 @@
 }
 
 // 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 @@
   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();