---

yaml
---
r: 30107
b: refs/heads/incoming
c: ff9151f
h: refs/heads/master
i:
  30105: 28463db
  30103: 2c26edf
v: v3

Author: pcwalton

[refs]

@@ -6,7 +6,7 @@ refs/heads/try: d324a424d8f84b1eb049b12cf34182bda91b0024
 refs/tags/release-0.1: 1f5c5126e96c79d22cb7862f75304136e204f105
 refs/heads/ndm: f3868061cd7988080c30d6d5bf352a5a5fe2460b
 refs/heads/try2: d0c6ce338884ee21843f4b40bf6bf18d222ce5df
-refs/heads/incoming: db71ff3eb61bbce3123f62b274100dadf5ca99a6
+refs/heads/incoming: ff9151fa55e4e81c0cbaa7181eb672b2df6b53f6
 refs/heads/dist-snap: 2f32a1581f522e524009138b33b1c7049ced668d
 refs/tags/release-0.2: c870d2dffb391e14efb05aa27898f1f6333a9596
 refs/tags/release-0.3: b5f0d0f648d9a6153664837026ba1be43d3e2503

branches/incoming/src/rustc/middle/trans/base.rs

@@ -278,7 +278,7 @@ fn alloca_maybe_zeroed(cx: block, t: TypeRef, zero: bool) -> ValueRef {
     if cx.unreachable { return llvm::LLVMGetUndef(t); }
     let initcx = raw_block(cx.fcx, false, cx.fcx.llstaticallocas);
     let p = Alloca(initcx, t);
-    if zero { Store(initcx, C_null(t), p); }
+    if zero { memzero(initcx, p, t); }
     return p;
 }
 
@@ -287,10 +287,38 @@ fn zero_mem(cx: block, llptr: ValueRef, t: ty::t) -> block {
     let bcx = cx;
     let ccx = cx.ccx();
     let llty = type_of(ccx, t);
-    Store(bcx, C_null(llty), llptr);
+    memzero(bcx, llptr, llty);
     return bcx;
 }
 
+// Always use this function instead of storing a zero constant to the memory
+// in question. If you store a zero constant, LLVM will drown in vreg
+// allocation for large data structures, and the generated code will be
+// awful. (A telltale sign of this is large quantities of
+// `mov [byte ptr foo],0` in the generated code.)
+fn memzero(cx: block, llptr: ValueRef, llty: TypeRef) {
+    let _icx = cx.insn_ctxt("memzero");
+    let ccx = cx.ccx();
+
+    let intrinsic_key;
+    match ccx.sess.targ_cfg.arch {
+        session::arch_x86 | session::arch_arm => {
+            intrinsic_key = ~"llvm.memset.p0i8.i32";
+        }
+        session::arch_x86_64 => {
+            intrinsic_key = ~"llvm.memset.p0i8.i64";
+        }
+    }
+
+    let llintrinsicfn = ccx.intrinsics.get(intrinsic_key);
+    let llptr = PointerCast(cx, llptr, T_ptr(T_i8()));
+    let llzeroval = C_u8(0);
+    let size = IntCast(cx, llsize_of(ccx, llty), ccx.int_type);
+    let align = C_i32(1i32);
+    let volatile = C_bool(false);
+    Call(cx, llintrinsicfn, ~[llptr, llzeroval, size, align, volatile]);
+}
+
 fn arrayalloca(cx: block, t: TypeRef, v: ValueRef) -> ValueRef {
     let _icx = cx.insn_ctxt("arrayalloca");
     if cx.unreachable { return llvm::LLVMGetUndef(t); }