Go patch committed: Fix order of evaluation

[Ian Lance Taylor]

This patch to the Go frontend fixes the order of evaluation for a
statement like m[0] = len(m) when m is a map.  I added a test case for
this to the master testsuite.  Bootstrapped and ran Go testsuite on
x86_64-unknown-linux-gnu.  Committed to mainline and 4.7 branch.

Ian


diff -r 5b5853844f00 go/gogo.cc
--- a/go/gogo.cc	Tue Apr 24 07:52:37 2012 -0700
+++ b/go/gogo.cc	Tue Apr 24 09:22:09 2012 -0700
@@ -2216,12 +2216,18 @@
       Expression::traverse(&init, &find_eval_ordering);
     }
 
-  if (find_eval_ordering.size() <= 1)
-    {
-      // If there is only one expression with a side-effect, we can
-      // leave it in place.
-      return TRAVERSE_CONTINUE;
-    }
+  size_t c = find_eval_ordering.size();
+  if (c == 0)
+    return TRAVERSE_CONTINUE;
+
+  // If there is only one expression with a side-effect, we can
+  // usually leave it in place.  However, for an assignment statement,
+  // we need to evaluate an expression on the right hand side before
+  // we evaluate any index expression on the left hand side, so for
+  // that case we always move the expression.  Otherwise we mishandle
+  // m[0] = len(m) where m is a map.
+  if (c == 1 && s->classification() != Statement::STATEMENT_ASSIGNMENT)
+    return TRAVERSE_CONTINUE;
 
   bool is_thunk = s->thunk_statement() != NULL;
   for (Find_eval_ordering::const_iterator p = find_eval_ordering.begin();