auto merge of #7259 : dotdash/rust/ir_improvement, r=graydon

The changes in these commits improve the IR codegen by removing unnecessary copies for certain function call arguments and stopping to allocate return values for functions returning nil. They reduce compile times by about 10% in total.

src/librustc/middle/trans/base.rs

@@ -1653,7 +1653,9 @@ pub fn new_fn_ctxt_w_id(ccx: @mut CrateContext,
     fcx.llenv = unsafe {
           llvm::LLVMGetParam(llfndecl, fcx.env_arg_pos() as c_uint)
     };
+    if !ty::type_is_nil(substd_output_type) {
         fcx.llretptr = Some(make_return_pointer(fcx, substd_output_type));
+    }
     fcx
 }
 
@@ -1808,7 +1810,7 @@ pub fn build_return_block(fcx: fn_ctxt) {
     let ret_cx = raw_block(fcx, false, fcx.llreturn);
 
     // Return the value if this function immediate; otherwise, return void.
-    if fcx.has_immediate_return_value {
+    if fcx.llretptr.is_some() && fcx.has_immediate_return_value {
         Ret(ret_cx, Load(ret_cx, fcx.llretptr.get()))
     } else {
         RetVoid(ret_cx)
@@ -2340,8 +2342,7 @@ pub fn create_entry_wrapper(ccx: @mut CrateContext,
             llvm::LLVMGetParam(llfdecl, env_arg as c_uint)
         };
         let args = ~[llenvarg];
-        let llresult = Call(bcx, main_llfn, args);
+        Call(bcx, main_llfn, args);
-        Store(bcx, llresult, fcx.llretptr.get());
 
         build_return(bcx);
         finish_fn(fcx, lltop);

src/librustc/middle/trans/cabi.rs

@@ -179,6 +179,7 @@ impl FnType {
             }
         }
 
+        if bcx.fcx.llretptr.is_some() {
             let llretval = load_inbounds(bcx, llargbundle, [ 0, arg_tys.len() ]);
             let llretval = if self.ret_ty.cast {
                 let retptr = BitCast(bcx, llretval, T_ptr(self.ret_ty.ty));
@@ -191,4 +192,5 @@ impl FnType {
                                    T_ptr(self.ret_ty.ty));
             Store(bcx, llretval, llretptr);
         }
+    }
 }

src/librustc/middle/trans/cabi_x86.rs

@@ -60,6 +60,11 @@ impl ABIInfo for X86_ABIInfo {
                 cast: false,
                 ty: T_void(),
             };
+        } else if !ret_def {
+            ret_ty = LLVMType {
+                cast: false,
+                ty: T_void()
+            };
         }
 
         return FnType {

src/librustc/middle/trans/callee.rs

@@ -801,6 +801,8 @@ pub fn trans_arg_expr(bcx: block,
                         val = arg_datum.to_ref_llval(bcx);
                     }
                     ty::ByCopy => {
+                        if ty::type_needs_drop(bcx.tcx(), arg_datum.ty) ||
+                                arg_datum.appropriate_mode().is_by_ref() {
                             debug!("by copy arg with type %s, storing to scratch",
                                    bcx.ty_to_str(arg_datum.ty));
                             let scratch = scratch_datum(bcx, arg_datum.ty, false);
@@ -816,10 +818,17 @@ pub fn trans_arg_expr(bcx: block,
                             scratch.add_clean(bcx);
                             temp_cleanups.push(scratch.val);
 
-                        match arg_datum.appropriate_mode() {
+                            match scratch.appropriate_mode() {
                                 ByValue => val = Load(bcx, scratch.val),
                                 ByRef(_) => val = scratch.val,
                             }
+                        } else {
+                            debug!("by copy arg with type %s");
+                            match arg_datum.mode {
+                                ByRef(_) => val = Load(bcx, arg_datum.val),
+                                ByValue => val = arg_datum.val,
+                            }
+                        }
                     }
                 }
             }

src/librustc/middle/trans/closure.rs

@@ -297,7 +297,10 @@ pub fn build_closure(bcx0: block,
         // the right thing):
         let ret_true = match bcx.fcx.loop_ret {
             Some((_, retptr)) => retptr,
-            None => bcx.fcx.llretptr.get()
+            None => match bcx.fcx.llretptr {
+                None => C_null(T_ptr(T_nil())),
+                Some(retptr) => retptr,
+            }
         };
         let ret_casted = PointerCast(bcx, ret_true, T_ptr(T_nil()));
         let ret_datum = Datum {val: ret_casted, ty: ty::mk_nil(),

src/librustc/middle/trans/controlflow.rs

@@ -298,24 +298,27 @@ pub fn trans_cont(bcx: block, label_opt: Option<ident>) -> block {
 pub fn trans_ret(bcx: block, e: Option<@ast::expr>) -> block {
     let _icx = bcx.insn_ctxt("trans_ret");
     let mut bcx = bcx;
-    let retptr = match copy bcx.fcx.loop_ret {
+    let dest = match copy bcx.fcx.loop_ret {
       Some((flagptr, retptr)) => {
         // This is a loop body return. Must set continue flag (our retptr)
         // to false, return flag to true, and then store the value in the
         // parent's retptr.
         Store(bcx, C_bool(true), flagptr);
         Store(bcx, C_bool(false), bcx.fcx.llretptr.get());
-        match e {
+        expr::SaveIn(match e {
           Some(x) => PointerCast(bcx, retptr,
                                  T_ptr(type_of(bcx.ccx(), expr_ty(bcx, x)))),
           None => retptr
+        })
       }
+      None => match bcx.fcx.llretptr {
+        None => expr::Ignore,
+        Some(retptr) => expr::SaveIn(retptr),
       }
-      None => bcx.fcx.llretptr.get()
     };
     match e {
       Some(x) => {
-        bcx = expr::trans_into(bcx, x, expr::SaveIn(retptr));
+        bcx = expr::trans_into(bcx, x, dest);
       }
       _ => ()
     }

src/librustc/middle/trans/foreign.rs

@@ -127,7 +127,7 @@ fn shim_types(ccx: @mut CrateContext, id: ast::node_id) -> ShimTypes {
         llsig: llsig,
         ret_def: ret_def,
         bundle_ty: bundle_ty,
-        shim_fn_ty: T_fn([T_ptr(bundle_ty)], T_nil()),
+        shim_fn_ty: T_fn([T_ptr(bundle_ty)], T_void()),
         fn_ty: fn_ty
     }
 }
@@ -170,7 +170,7 @@ fn build_shim_fn_(ccx: @mut CrateContext,
     tie_up_header_blocks(fcx, lltop);
 
     let ret_cx = raw_block(fcx, false, fcx.llreturn);
-    Ret(ret_cx, C_null(T_nil()));
+    RetVoid(ret_cx);
 
     return llshimfn;
 }
@@ -530,8 +530,10 @@ pub fn trans_foreign_mod(ccx: @mut CrateContext,
 
                 store_inbounds(bcx, llargval, llargbundle, [0u, i]);
             }
-            let llretptr = bcx.fcx.llretptr.get();
+
-            store_inbounds(bcx, llretptr, llargbundle, [0u, n]);
+            for bcx.fcx.llretptr.iter().advance |&retptr| {
+                store_inbounds(bcx, retptr, llargbundle, [0u, n]);
+            }
         }
 
         fn build_ret(bcx: block,
@@ -539,8 +541,10 @@ pub fn trans_foreign_mod(ccx: @mut CrateContext,
                      llargbundle: ValueRef) {
             let _icx = bcx.insn_ctxt("foreign::wrap::build_ret");
             let arg_count = shim_types.fn_sig.inputs.len();
+            for bcx.fcx.llretptr.iter().advance |&retptr| {
                 let llretptr = load_inbounds(bcx, llargbundle, [0, arg_count]);
-            Store(bcx, Load(bcx, llretptr), bcx.fcx.llretptr.get());
+                Store(bcx, Load(bcx, llretptr), retptr);
+            }
             build_return(bcx);
         }
     }
@@ -1294,7 +1298,7 @@ pub fn trans_foreign_fn(ccx: @mut CrateContext,
                      shim_types: &ShimTypes,
                      llargbundle: ValueRef,
                      llretval: ValueRef) {
-            if ty::type_is_immediate(shim_types.fn_sig.output) {
+            if bcx.fcx.llretptr.is_some() && ty::type_is_immediate(shim_types.fn_sig.output) {
                 // Write the value into the argument bundle.
                 let arg_count = shim_types.fn_sig.inputs.len();
                 let llretptr = load_inbounds(bcx,

src/librustc/middle/trans/type_of.rs

@@ -55,7 +55,7 @@ pub fn type_of_fn(cx: &mut CrateContext, inputs: &[ty::t], output: ty::t)
         atys.push_all(type_of_explicit_args(cx, inputs));
 
         // Use the output as the actual return value if it's immediate.
-        if output_is_immediate {
+        if output_is_immediate && !ty::type_is_nil(output) {
             T_fn(atys, lloutputtype)
         } else {
             T_fn(atys, llvm::LLVMVoidTypeInContext(cx.llcx))
@@ -352,7 +352,7 @@ pub fn llvm_type_name(cx: &CrateContext,
 }
 
 pub fn type_of_dtor(ccx: &mut CrateContext, self_ty: ty::t) -> TypeRef {
-    T_fn([T_ptr(type_of(ccx, self_ty))] /* self */, T_nil())
+    T_fn([T_ptr(type_of(ccx, self_ty))] /* self */, T_void())
 }
 
 pub fn type_of_rooted(ccx: &mut CrateContext, t: ty::t) -> TypeRef {
@@ -364,5 +364,5 @@ pub fn type_of_rooted(ccx: &mut CrateContext, t: ty::t) -> TypeRef {
 
 pub fn type_of_glue_fn(ccx: &CrateContext) -> TypeRef {
     let tydescpp = T_ptr(T_ptr(ccx.tydesc_type));
-    return T_fn([T_ptr(T_nil()), tydescpp, T_ptr(T_i8())], T_nil());
+    return T_fn([T_ptr(T_nil()), tydescpp, T_ptr(T_i8())], T_void());
 }