===================================================================
@@ -1,4 +1,4 @@
-b1ae35965cadac235d7d218e689944286cccdd90
+62d1b667f3e85f72a186b04aad36d701160a4611
The first line of this file holds the git revision number of the last
merge done from the gofrontend repository.
===================================================================
@@ -7408,6 +7408,26 @@ String_concat_expression::do_flatten(Gog
return this;
Location loc = this->location();
Type* type = this->type();
+
+ // Mark string([]byte) operands to reuse the backing store.
+ // runtime.concatstrings does not keep the reference.
+ //
+ // Note: in the gc runtime, if all but one inputs are empty,
+ // concatstrings returns the only nonempty input without copy.
+ // So it is not safe to reuse the backing store if it is a
+ // string([]byte) conversion. So the gc compiler does the
+ // no-copy optimization only when there is at least one
+ // constant nonempty input. Currently the gccgo runtime
+ // doesn't do this, so we don't do the check.
+ for (Expression_list::iterator p = this->exprs_->begin();
+ p != this->exprs_->end();
+ ++p)
+ {
+ Type_conversion_expression* tce = (*p)->conversion_expression();
+ if (tce != NULL)
+ tce->set_no_copy(true);
+ }
+
Expression* nil_arg = Expression::make_nil(loc);
Expression* call;
switch (this->exprs_->size())
===================================================================
@@ -0,0 +1,8 @@
+// { dg-do compile }
+// { dg-options "-fgo-debug-optimization" }
+
+package p
+
+func F(b []byte, x string) string {
+ return "hello " + string(b) + x // { dg-error "no copy string\\(\\\[\\\]byte\\)" }
+}