Remove optimize_function

It currently doesn't have any optimizations at all.

src/base.rs

@@ -148,7 +148,7 @@ fn compile_fn<'tcx>(
 ) {
     let tcx = cx.tcx;
 
-    let mut clif_comments = codegened_func.clif_comments;
+    let clif_comments = codegened_func.clif_comments;
 
     // Store function in context
     let context = cached_context;
@@ -165,17 +165,6 @@ fn compile_fn<'tcx>(
     // invalidate it when it would change.
     context.domtree.clear();
 
-    // Perform rust specific optimizations
-    tcx.sess.time("optimize clif ir", || {
-        crate::optimize::optimize_function(
-            tcx,
-            module.isa(),
-            codegened_func.instance,
-            context,
-            &mut clif_comments,
-        );
-    });
-
     #[cfg(any())] // This is never true
     let _clif_guard = {
         use std::fmt::Write;

src/optimize/mod.rs

@@ -1,20 +1,3 @@
 //! Various optimizations specific to cg_clif
 
-use cranelift_codegen::isa::TargetIsa;
-
-use crate::prelude::*;
-
 pub(crate) mod peephole;
-
-pub(crate) fn optimize_function<'tcx>(
-    tcx: TyCtxt<'tcx>,
-    isa: &dyn TargetIsa,
-    instance: Instance<'tcx>,
-    ctx: &mut Context,
-    clif_comments: &mut crate::pretty_clif::CommentWriter,
-) {
-    // FIXME classify optimizations over opt levels once we have more
-
-    crate::pretty_clif::write_clif_file(tcx, "preopt", isa, instance, &ctx.func, &*clif_comments);
-    crate::base::verify_func(tcx, &*clif_comments, &ctx.func);
-}