From 0859e5ebb319ceddcce01ddb63470d8f59860aba Mon Sep 17 00:00:00 2001
From: James Miller <james@aatch.net>
Date: Sat, 17 Jan 2015 17:04:15 +1300
Subject: [PATCH] Use `zero_mem` instead of a zerointializer for `init`
 intrinsic

LLVM gets overwhelmed when presented with a zeroinitializer for a large
type. In unoptimised builds, it generates a long sequence of stores to
memory. In optmised builds, it manages to generate a standard memset of
zero values, but takes a long time doing so.

Call out to the `llvm.memset` function to zero out the memory instead.
---
 src/librustc_trans/trans/intrinsic.rs | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/src/librustc_trans/trans/intrinsic.rs b/src/librustc_trans/trans/intrinsic.rs
index 91c7409182d..eaf9b4a6bf7 100644
--- a/src/librustc_trans/trans/intrinsic.rs
+++ b/src/librustc_trans/trans/intrinsic.rs
@@ -361,12 +361,11 @@ pub fn trans_intrinsic_call<'a, 'blk, 'tcx>(mut bcx: Block<'blk, 'tcx>,
         }
         (_, "init") => {
             let tp_ty = *substs.types.get(FnSpace, 0);
-            let lltp_ty = type_of::arg_type_of(ccx, tp_ty);
-            if return_type_is_void(ccx, tp_ty) {
-                C_nil(ccx)
-            } else {
-                C_null(lltp_ty)
+            if !return_type_is_void(ccx, tp_ty) {
+                // Just zero out the stack slot
+                zero_mem(bcx, llresult, tp_ty);
             }
+            C_nil(ccx)
         }
         // Effectively no-ops
         (_, "uninit") | (_, "forget") => {