Rollup merge of rust-lang#22969 - dotdash:no_alloca_zeroed, r=huonw

 Its only user was lvalue_scratch_datum which is called with zero=true
anymore, so it's effectively unused.

Author: Manishearth

src/librustc_trans/trans/adt.rs

@@ -1000,7 +1000,7 @@ pub fn trans_drop_flag_ptr<'blk, 'tcx>(mut bcx: Block<'blk, 'tcx>, r: &Repr<'tcx
             let fcx = bcx.fcx;
             let custom_cleanup_scope = fcx.push_custom_cleanup_scope();
             let scratch = unpack_datum!(bcx, datum::lvalue_scratch_datum(
-                bcx, tcx.types.bool, "drop_flag", false,
+                bcx, tcx.types.bool, "drop_flag",
                 cleanup::CustomScope(custom_cleanup_scope), (), |_, bcx, _| bcx
             ));
             bcx = fold_variants(bcx, r, val, |variant_cx, st, value| {

src/librustc_trans/trans/base.rs

@@ -1203,21 +1203,6 @@ pub fn alloca_no_lifetime(cx: Block, ty: Type, name: &str) -> ValueRef {
     Alloca(cx, ty, name)
 }
 
-pub fn alloca_zeroed<'blk, 'tcx>(cx: Block<'blk, 'tcx>, ty: Ty<'tcx>,
-                                 name: &str) -> ValueRef {
-    let llty = type_of::type_of(cx.ccx(), ty);
-    if cx.unreachable.get() {
-        unsafe {
-            return llvm::LLVMGetUndef(llty.ptr_to().to_ref());
-        }
-    }
-    let p = alloca_no_lifetime(cx, llty, name);
-    let b = cx.fcx.ccx.builder();
-    b.position_before(cx.fcx.alloca_insert_pt.get().unwrap());
-    memzero(&b, p, ty);
-    p
-}
-
 // Creates the alloca slot which holds the pointer to the slot for the final return value
 pub fn make_return_slot_pointer<'a, 'tcx>(fcx: &FunctionContext<'a, 'tcx>,
                                           output_type: Ty<'tcx>) -> ValueRef {
@@ -1547,7 +1532,6 @@ fn create_datums_for_fn_args_under_call_abi<'blk, 'tcx>(
                                   datum::lvalue_scratch_datum(bcx,
                                                               arg_ty,
                                                               "tupled_args",
-                                                              false,
                                                               tuple_args_scope_id,
                                                               (),
                                                               |(),

src/librustc_trans/trans/datum.rs

@@ -195,24 +195,18 @@ pub fn immediate_rvalue_bcx<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
 
 /// Allocates temporary space on the stack using alloca() and returns a by-ref Datum pointing to
 /// it. The memory will be dropped upon exit from `scope`. The callback `populate` should
-/// initialize the memory. If `zero` is true, the space will be zeroed when it is allocated; this
-/// is not necessary unless `bcx` does not dominate the end of `scope`.
+/// initialize the memory.
 pub fn lvalue_scratch_datum<'blk, 'tcx, A, F>(bcx: Block<'blk, 'tcx>,
                                               ty: Ty<'tcx>,
                                               name: &str,
-                                              zero: bool,
                                               scope: cleanup::ScopeId,
                                               arg: A,
                                               populate: F)
                                               -> DatumBlock<'blk, 'tcx, Lvalue> where
     F: FnOnce(A, Block<'blk, 'tcx>, ValueRef) -> Block<'blk, 'tcx>,
 {
-    let scratch = if zero {
-        alloca_zeroed(bcx, ty, name)
-    } else {
-        let llty = type_of::type_of(bcx.ccx(), ty);
-        alloca(bcx, llty, name)
-    };
+    let llty = type_of::type_of(bcx.ccx(), ty);
+    let scratch = alloca(bcx, llty, name);
 
     // Subtle. Populate the scratch memory *before* scheduling cleanup.
     let bcx = populate(arg, bcx, scratch);
@@ -383,7 +377,7 @@ impl<'tcx> Datum<'tcx, Rvalue> {
 
             ByValue => {
                 lvalue_scratch_datum(
-                    bcx, self.ty, name, false, scope, self,
+                    bcx, self.ty, name, scope, self,
                     |this, bcx, llval| this.store_to(bcx, llval))
             }
         }