do not stringify AST nodes unless emitting comments

Author: nikomatsakis

src/comp/middle/trans.rs

@@ -4536,7 +4536,9 @@ fn zero_alloca(cx: @block_ctxt, llptr: ValueRef, t: ty::t)
 fn trans_stmt(cx: @block_ctxt, s: ast::stmt) -> @block_ctxt {
     // FIXME Fill in cx.sp
 
-    add_span_comment(cx, s.span, stmt_to_str(s));
+    if (!bcx_ccx(cx).sess.get_opts().no_asm_comments) {
+        add_span_comment(cx, s.span, stmt_to_str(s));
+    }
 
     let bcx = cx;
     alt s.node {

src/comp/middle/trans_build.rs

@@ -515,7 +515,9 @@ fn add_span_comment(bcx: @block_ctxt, sp: span, text: str) {
 fn add_comment(bcx: @block_ctxt, text: str) {
     let ccx = bcx_ccx(bcx);
     if (!ccx.sess.get_opts().no_asm_comments) {
-        let comment_text = "; " + text;
+        check str::is_not_empty("$");
+        let sanitized = str::replace(text, "$", "");
+        let comment_text = "; " + sanitized;
         let asm = str::as_buf(comment_text, { |c|
             str::as_buf("", { |e|
                 llvm::LLVMConstInlineAsm(T_fn([], T_void()), c, e, 0, 0)})});