Auto merge of #113116 - nnethercote:codegen-opts, r=oli-obk

A mish-mash of micro-optimizations

These were aimed at speeding up LLVM codegen, but ended up affecting other places as well.

r? `@bjorn3`

src/debuginfo/line_info.rs

@@ -81,7 +81,7 @@ impl DebugContext {
 
         match tcx.sess.source_map().lookup_line(span.lo()) {
             Ok(SourceFileAndLine { sf: file, line }) => {
-                let line_pos = file.line_begin_pos(span.lo());
+                let line_pos = file.lines(|lines| lines[line]);
 
                 (
                     file,