commit d16e370c93e2866a961847a15f5001413e66d179
author Than McIntosh <thanm@google.com> Tue Dec 05 09:27:46 2017 -0500
committer Ian Lance Taylor <iant@golang.org> Wed Dec 06 13:31:12 2017 +0000
tree af3a67426a3446d16d6421bb0f75da809c920c5f
parent 297cf346f2400274946650ab9ecd039427fc986b

compiler: handle set-and-use-temp in nilcheck code

Change the code in Unary_expression::do_get_backend that introduces
explicit nil checks for dereference operations to special case
set-and-use-temporary expressions. For this case it is better to
generate an explicit reference of the temp in the final conditional
(avoids introducing tree sharing).

Change-Id: Ic7d83605d93212af36ef8f069ffbb080e9697db8
Reviewed-on: https://go-review.googlesource.com/81915
Reviewed-by: Ian Lance Taylor <iant@golang.org>

go/expressions.cc

diff --git a/go/expressions.cc b/go/expressions.cc
index e9b8683..219b163 100644
--- a/go/expressions.cc
+++ b/go/expressions.cc
@@ -4455,10 +4455,23 @@
             case NIL_CHECK_NEEDED:
               {
                 go_assert(this->expr_->is_variable());
+
+                // If we're nil-checking the result of a set-and-use-temporary
+                // expression, then pick out the target temp and use that
+                // for the final result of the conditional.
+                Bexpression* tbexpr = bexpr;
+                Bexpression* ubexpr = bexpr;
+                Set_and_use_temporary_expression* sut =
+                    this->expr_->set_and_use_temporary_expression();
+                if (sut != NULL) {
+                  Temporary_statement* temp = sut->temporary();
+                  Bvariable* bvar = temp->get_backend_variable(context);
+                  ubexpr = gogo->backend()->var_expression(bvar, loc);
+                }
                 Bexpression* nil =
                     Expression::make_nil(loc)->get_backend(context);
                 Bexpression* compare =
-                    gogo->backend()->binary_expression(OPERATOR_EQEQ, bexpr,
+                    gogo->backend()->binary_expression(OPERATOR_EQEQ, tbexpr,
                                                        nil, loc);
                 Bexpression* crash =
                     gogo->runtime_error(RUNTIME_ERROR_NIL_DEREFERENCE,
@@ -4466,7 +4479,7 @@
                 Bfunction* bfn = context->function()->func_value()->get_decl();
                 bexpr = gogo->backend()->conditional_expression(bfn, btype,
                                                                 compare,
-                                                                crash, bexpr,
+                                                                crash, ubexpr,
                                                                 loc);
                 known_valid = true;
                 break;