From 2a40c5db469b5065f64c69ae7874f162ff2669a8 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn=20Steinbrink?= <bsteinbr@gmail.com>
Date: Sat, 29 Jun 2013 16:43:39 +0200
Subject: [PATCH] Avoid extra casts for "self" arguments

"self" is always passed as an opaque box, so there's no point in using
the concrete self type when translating the argument. All it does it
causing the value to be casted back to an opaque box right away.
---
 src/librustc/middle/trans/callee.rs |  9 +--------
 src/librustc/middle/trans/meth.rs   | 29 +++++++----------------------
 2 files changed, 8 insertions(+), 30 deletions(-)

diff --git a/src/librustc/middle/trans/callee.rs b/src/librustc/middle/trans/callee.rs
index 8ef55f89d81..6d139130e2b 100644
--- a/src/librustc/middle/trans/callee.rs
+++ b/src/librustc/middle/trans/callee.rs
@@ -615,10 +615,7 @@ pub fn trans_call_inner(in_cx: block,
                 }
                 Method(d) => {
                     // Weird but true: we pass self in the *environment* slot!
-                    let llself = PointerCast(bcx,
-                                             d.llself,
-                                             Type::opaque_box(ccx).ptr_to());
-                    (d.llfn, llself)
+                    (d.llfn, d.llself)
                 }
                 Closure(d) => {
                     // Closures are represented as (llfn, llclosure) pair:
@@ -944,10 +941,6 @@ pub fn trans_arg_expr(bcx: block,
         if formal_arg_ty != arg_datum.ty {
             // this could happen due to e.g. subtyping
             let llformal_arg_ty = type_of::type_of_explicit_arg(ccx, &formal_arg_ty);
-            let llformal_arg_ty = match self_mode {
-                ty::ByRef => llformal_arg_ty.ptr_to(),
-                ty::ByCopy => llformal_arg_ty,
-            };
             debug!("casting actual type (%s) to match formal (%s)",
                    bcx.val_to_str(val), bcx.llty_str(llformal_arg_ty));
             val = PointerCast(bcx, val, llformal_arg_ty);
diff --git a/src/librustc/middle/trans/meth.rs b/src/librustc/middle/trans/meth.rs
index 0b051662781..fa32dd5b93e 100644
--- a/src/librustc/middle/trans/meth.rs
+++ b/src/librustc/middle/trans/meth.rs
@@ -133,8 +133,8 @@ pub fn trans_self_arg(bcx: block,
     let _icx = push_ctxt("impl::trans_self_arg");
     let mut temp_cleanups = ~[];
 
-    // Compute the type of self.
-    let self_ty = monomorphize_type(bcx, mentry.self_ty);
+    // self is passed as an opaque box in the environment slot
+    let self_ty = ty::mk_opaque_box(bcx.tcx());
     let result = trans_arg_expr(bcx,
                                 self_ty,
                                 mentry.self_mode,
@@ -576,7 +576,6 @@ pub fn trans_trait_callee_from_llval(bcx: block,
     let llbox = Load(bcx, GEPi(bcx, llpair, [0u, abi::trt_field_box]));
 
     // Munge `llself` appropriately for the type of `self` in the method.
-    let self_mode;
     match explicit_self {
         ast::sty_static => {
             bcx.tcx().sess.bug("shouldn't see static method here");
@@ -597,12 +596,6 @@ pub fn trans_trait_callee_from_llval(bcx: block,
                     llself = llbox;
                 }
             }
-
-            let llscratch = alloca(bcx, val_ty(llself));
-            Store(bcx, llself, llscratch);
-            llself = llscratch;
-
-            self_mode = ty::ByRef;
         }
         ast::sty_box(_) => {
             // Bump the reference count on the box.
@@ -615,12 +608,6 @@ pub fn trans_trait_callee_from_llval(bcx: block,
                 ty::BoxTraitStore => llself = llbox,
                 _ => bcx.tcx().sess.bug("@self receiver with non-@Trait")
             }
-
-            let llscratch = alloca(bcx, val_ty(llself));
-            Store(bcx, llself, llscratch);
-            llself = llscratch;
-
-            self_mode = ty::ByRef;
         }
         ast::sty_uniq(_) => {
             // Pass the unique pointer.
@@ -628,15 +615,13 @@ pub fn trans_trait_callee_from_llval(bcx: block,
                 ty::UniqTraitStore => llself = llbox,
                 _ => bcx.tcx().sess.bug("~self receiver with non-~Trait")
             }
-
-            let llscratch = alloca(bcx, val_ty(llself));
-            Store(bcx, llself, llscratch);
-            llself = llscratch;
-
-            self_mode = ty::ByRef;
         }
     }
 
+    let llscratch = alloca(bcx, val_ty(llself));
+    Store(bcx, llself, llscratch);
+    llself = PointerCast(bcx, llscratch, Type::opaque_box(ccx).ptr_to());
+
     // Load the function from the vtable and cast it to the expected type.
     debug!("(translating trait callee) loading method");
     let llcallee_ty = type_of_fn_from_ty(ccx, callee_ty);
@@ -652,7 +637,7 @@ pub fn trans_trait_callee_from_llval(bcx: block,
             llfn: mptr,
             llself: llself,
             self_ty: ty::mk_opaque_box(bcx.tcx()),
-            self_mode: self_mode,
+            self_mode: ty::ByRef,
             explicit_self: explicit_self
             /* XXX: Some(llbox) */
         })