go patch committed: Avoid double error on negative shift count

[Ian Lance Taylor]

This patch to the Go frontend avoids a double error when there is a
negative shift count.  We used to give a negative shift count error
followed by an overflow error.  This just gives the former.
Bootstrapped and ran Go testsuite on x86_64-unknown-linux-gnu.
Committed to mainline.

Ian


diff -r 31aaf6e2aa75 go/expressions.cc
--- a/go/expressions.cc	Fri Mar 25 10:32:02 2011 -0700
+++ b/go/expressions.cc	Fri Mar 25 12:20:47 2011 -0700
@@ -5747,7 +5747,13 @@
 	  if (this->right_->integer_constant_value(true, val, &type))
 	    {
 	      if (mpz_sgn(val) < 0)
-		this->report_error(_("negative shift count"));
+		{
+		  this->report_error(_("negative shift count"));
+		  mpz_set_ui(val, 0);
+		  source_location rloc = this->right_->location();
+		  this->right_ = Expression::make_integer(&val, right_type,
+							  rloc);
+		}
 	    }
 	  mpz_clear(val);
 	}