Go patch committed: Avoid infinite recursion in string constant eval

[Ian Lance Taylor]

This patch from Rémy Oudompheng avoids an infinite recursion in the Go
frontend when evaluating a string constant.  It avoids a compiler crash
on invalid code like 
    const f, g = g, f
    func S() []byte { return []byte(f) }
Bootstrapped and ran Go testsuite on x86_64-unknown-linux-gnu.
Committed to mainline and 4.7 branch.

Ian


diff -r 3271745b0eb0 go/expressions.cc
--- a/go/expressions.cc	Wed Apr 04 11:49:50 2012 -0700
+++ b/go/expressions.cc	Mon Apr 16 15:57:40 2012 -0700
@@ -2403,8 +2403,7 @@
   do_numeric_constant_value(Numeric_constant* nc) const;
 
   bool
-  do_string_constant_value(std::string* val) const
-  { return this->constant_->const_value()->expr()->string_constant_value(val); }
+  do_string_constant_value(std::string* val) const;
 
   Type*
   do_type();
@@ -2514,6 +2513,21 @@
   return r;
 }
 
+bool
+Const_expression::do_string_constant_value(std::string* val) const
+{
+  if (this->seen_)
+    return false;
+
+  Expression* e = this->constant_->const_value()->expr();
+
+  this->seen_ = true;
+  bool ok = e->string_constant_value(val);
+  this->seen_ = false;
+
+  return ok;
+}
+
 // Return the type of the const reference.
 
 Type*