benchmark ignoring span hashes during incr. comp. for getting a lower…

… bound for rust-lang#47389

src/librustc/ich/hcx.rs

@@ -320,7 +320,7 @@ impl<'a> HashStable<StableHashingContext<'a>> for Span {
         const TAG_EXPANSION: u8 = 0;
         const TAG_NO_EXPANSION: u8 = 1;
 
-        if !hcx.hash_spans {
+        if !hcx.hash_spans && false {
             return
         }