rustc: encode scalar pairs in layout ABI.

15 files changed, 266 insertions, 137 deletions

diff --git a/src/librustc/ty/layout.rs b/src/librustc/ty/layout.rs
index 0edd8f44f0c..21ba7995332 100644
--- a/src/librustc/ty/layout.rs
+++ b/src/librustc/ty/layout.rs
@@ -757,6 +757,7 @@ impl FieldPlacement {
 pub enum Abi {
     Uninhabited,
     Scalar(Scalar),
+    ScalarPair(Scalar, Scalar),
     Vector,
     Aggregate {
         /// If true, the size is exact, otherwise it's only a lower bound.
@@ -769,7 +770,10 @@ impl Abi {
     /// Returns true if the layout corresponds to an unsized type.
     pub fn is_unsized(&self) -> bool {
         match *self {
-            Abi::Uninhabited | Abi::Scalar(_) | Abi::Vector => false,
+            Abi::Uninhabited |
+            Abi::Scalar(_) |
+            Abi::ScalarPair(..) |
+            Abi::Vector => false,
             Abi::Aggregate { sized, .. } => !sized
         }
     }
@@ -777,7 +781,10 @@ impl Abi {
     /// Returns true if the fields of the layout are packed.
     pub fn is_packed(&self) -> bool {
         match *self {
-            Abi::Uninhabited | Abi::Scalar(_) | Abi::Vector => false,
+            Abi::Uninhabited |
+            Abi::Scalar(_) |
+            Abi::ScalarPair(..) |
+            Abi::Vector => false,
             Abi::Aggregate { packed, .. } => packed
         }
     }
@@ -905,13 +912,32 @@ impl<'a, 'tcx> CachedLayout {
                         -> Result<&'tcx Self, LayoutError<'tcx>> {
         let cx = (tcx, param_env);
         let dl = cx.data_layout();
-        let scalar = |value: Primitive| {
+        let scalar_unit = |value: Primitive| {
             let bits = value.size(dl).bits();
             assert!(bits <= 128);
-            tcx.intern_layout(CachedLayout::scalar(cx, Scalar {
+            Scalar {
                 value,
                 valid_range: 0..=(!0 >> (128 - bits))
-            }))
+            }
+        };
+        let scalar = |value: Primitive| {
+            tcx.intern_layout(CachedLayout::scalar(cx, scalar_unit(value)))
+        };
+        let scalar_pair = |a: Scalar, b: Scalar| {
+            let align = a.value.align(dl).max(b.value.align(dl)).max(dl.aggregate_align);
+            let b_offset = a.value.size(dl).abi_align(b.value.align(dl));
+            let size = (b_offset + b.value.size(dl)).abi_align(align);
+            CachedLayout {
+                variants: Variants::Single { index: 0 },
+                fields: FieldPlacement::Arbitrary {
+                    offsets: vec![Size::from_bytes(0), b_offset],
+                    memory_index: vec![0, 1]
+                },
+                abi: Abi::ScalarPair(a, b),
+                align,
+                primitive_align: align,
+                size
+            }
         };
 
         #[derive(Copy, Clone, Debug)]
@@ -1049,19 +1075,54 @@ impl<'a, 'tcx> CachedLayout {
                 memory_index = inverse_memory_index;
             }
 
+            let size = min_size.abi_align(align);
+            let mut abi = Abi::Aggregate {
+                sized,
+                packed
+            };
+
+            // Look for a scalar pair, as an ABI optimization.
+            // FIXME(eddyb) ignore extra ZST fields and field ordering.
+            if sized && !packed && fields.len() == 2 {
+                match (&fields[0].abi, &fields[1].abi) {
+                    (&Abi::Scalar(ref a), &Abi::Scalar(ref b)) => {
+                        let pair = scalar_pair(a.clone(), b.clone());
+                        let pair_offsets = match pair.fields {
+                            FieldPlacement::Arbitrary {
+                                ref offsets,
+                                ref memory_index
+                            } => {
+                                assert_eq!(memory_index, &[0, 1]);
+                                offsets
+                            }
+                            _ => bug!()
+                        };
+                        if offsets[0] == pair_offsets[0] &&
+                           offsets[1] == pair_offsets[1] &&
+                           memory_index[0] == 0 &&
+                           memory_index[1] == 1 &&
+                           align == pair.align &&
+                           primitive_align == pair.primitive_align &&
+                           size == pair.size {
+                            // We can use `ScalarPair` only when it matches our
+                            // already computed layout (including `#[repr(C)]`).
+                            abi = pair.abi;
+                        }
+                    }
+                    _ => {}
+                }
+            }
+
             Ok(CachedLayout {
                 variants: Variants::Single { index: 0 },
                 fields: FieldPlacement::Arbitrary {
                     offsets,
                     memory_index
                 },
-                abi: Abi::Aggregate {
-                    sized,
-                    packed
-                },
+                abi,
                 align,
                 primitive_align,
-                size: min_size.abi_align(align)
+                size
             })
         };
         let univariant = |fields: &[TyLayout], repr: &ReprOptions, kind| {
@@ -1070,45 +1131,34 @@ impl<'a, 'tcx> CachedLayout {
         assert!(!ty.has_infer_types());
 
         let ptr_layout = |pointee: Ty<'tcx>| {
+            let mut data_ptr = scalar_unit(Pointer);
+            if !ty.is_unsafe_ptr() {
+                data_ptr.valid_range.start = 1;
+            }
+
             let pointee = tcx.normalize_associated_type_in_env(&pointee, param_env);
             if pointee.is_sized(tcx, param_env, DUMMY_SP) {
-                let non_zero = !ty.is_unsafe_ptr();
-                let bits = Pointer.size(dl).bits();
-                return Ok(tcx.intern_layout(CachedLayout::scalar(cx, Scalar {
-                    value: Pointer,
-                    valid_range: (non_zero as u128)..=(!0 >> (128 - bits))
-                })));
+                return Ok(tcx.intern_layout(CachedLayout::scalar(cx, data_ptr)));
             }
 
             let unsized_part = tcx.struct_tail(pointee);
             let metadata = match unsized_part.sty {
-                ty::TyForeign(..) => return Ok(scalar(Pointer)),
+                ty::TyForeign(..) => {
+                    return Ok(tcx.intern_layout(CachedLayout::scalar(cx, data_ptr)));
+                }
                 ty::TySlice(_) | ty::TyStr => {
-                    Int(dl.ptr_sized_integer(), false)
+                    scalar_unit(Int(dl.ptr_sized_integer(), false))
+                }
+                ty::TyDynamic(..) => {
+                    let mut vtable = scalar_unit(Pointer);
+                    vtable.valid_range.start = 1;
+                    vtable
                 }
-                ty::TyDynamic(..) => Pointer,
                 _ => return Err(LayoutError::Unknown(unsized_part))
             };
 
             // Effectively a (ptr, meta) tuple.
-            let align = Pointer.align(dl).max(metadata.align(dl));
-            let meta_offset = Pointer.size(dl);
-            assert_eq!(meta_offset, meta_offset.abi_align(metadata.align(dl)));
-            let fields = FieldPlacement::Arbitrary {
-                offsets: vec![Size::from_bytes(0), meta_offset],
-                memory_index: vec![0, 1]
-            };
-            Ok(tcx.intern_layout(CachedLayout {
-                variants: Variants::Single { index: 0 },
-                fields,
-                abi: Abi::Aggregate {
-                    sized: true,
-                    packed: false
-                },
-                align,
-                primitive_align: align,
-                size: (meta_offset + metadata.size(dl)).abi_align(align)
-            }))
+            Ok(tcx.intern_layout(scalar_pair(data_ptr, metadata)))
         };
 
         Ok(match ty.sty {
@@ -1134,11 +1184,9 @@ impl<'a, 'tcx> CachedLayout {
             ty::TyFloat(FloatTy::F32) => scalar(F32),
             ty::TyFloat(FloatTy::F64) => scalar(F64),
             ty::TyFnPtr(_) => {
-                let bits = Pointer.size(dl).bits();
-                tcx.intern_layout(CachedLayout::scalar(cx, Scalar {
-                    value: Pointer,
-                    valid_range: 1..=(!0 >> (128 - bits))
-                }))
+                let mut ptr = scalar_unit(Pointer);
+                ptr.valid_range.start = 1;
+                tcx.intern_layout(CachedLayout::scalar(cx, ptr))
             }
 
             // The never type.
@@ -2194,7 +2242,7 @@ impl<'a, 'tcx> TyLayout<'tcx> {
     pub fn is_zst(&self) -> bool {
         match self.abi {
             Abi::Uninhabited => true,
-            Abi::Scalar(_) => false,
+            Abi::Scalar(_) | Abi::ScalarPair(..) => false,
             Abi::Vector => self.size.bytes() == 0,
             Abi::Aggregate { sized, .. } => sized && self.size.bytes() == 0
         }
@@ -2347,6 +2395,10 @@ impl<'gcx> HashStable<StableHashingContext<'gcx>> for Abi {
             Scalar(ref value) => {
                 value.hash_stable(hcx, hasher);
             }
+            ScalarPair(ref a, ref b) => {
+                a.hash_stable(hcx, hasher);
+                b.hash_stable(hcx, hasher);
+            }
             Vector => {}
             Aggregate { packed, sized } => {
                 packed.hash_stable(hcx, hasher);
diff --git a/src/librustc_trans/abi.rs b/src/librustc_trans/abi.rs
index 54e648c6d4a..d69103bbb52 100644
--- a/src/librustc_trans/abi.rs
+++ b/src/librustc_trans/abi.rs
@@ -311,6 +311,7 @@ impl<'tcx> LayoutExt<'tcx> for TyLayout<'tcx> {
             layout::Abi::Uninhabited |
             layout::Abi::Scalar(_) |
             layout::Abi::Vector => false,
+            layout::Abi::ScalarPair(..) |
             layout::Abi::Aggregate { .. } => true
         }
     }
@@ -340,6 +341,7 @@ impl<'tcx> LayoutExt<'tcx> for TyLayout<'tcx> {
                 })
             }
 
+            layout::Abi::ScalarPair(..) |
             layout::Abi::Aggregate { .. } => {
                 let mut total = Size::from_bytes(0);
                 let mut result = None;
@@ -745,10 +747,13 @@ impl<'a, 'tcx> FnType<'tcx> {
                         arg.attrs.set(ArgAttribute::NonNull);
                     }
                 }
-                _ => {}
+                _ => {
+                    // Nothing to do for non-pointer types.
+                    return;
+                }
             }
 
-            if let Some(pointee) = arg.layout.pointee_info(ccx) {
+            if let Some(pointee) = arg.layout.pointee_info_at(ccx, Size::from_bytes(0)) {
                 if let Some(kind) = pointee.safe {
                     arg.attrs.pointee_size = pointee.size;
                     arg.attrs.pointee_align = Some(pointee.align);
diff --git a/src/librustc_trans/cabi_x86_64.rs b/src/librustc_trans/cabi_x86_64.rs
index 62540fac8b5..eeb69276500 100644
--- a/src/librustc_trans/cabi_x86_64.rs
+++ b/src/librustc_trans/cabi_x86_64.rs
@@ -88,6 +88,7 @@ fn classify_arg<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>, arg: &ArgType<'tcx>)
                 }
             }
 
+            layout::Abi::ScalarPair(..) |
             layout::Abi::Aggregate { .. } => {
                 match layout.variants {
                     layout::Variants::Single { .. } => {
diff --git a/src/librustc_trans/cabi_x86_win64.rs b/src/librustc_trans/cabi_x86_win64.rs
index e93eeb83619..473c00120a7 100644
--- a/src/librustc_trans/cabi_x86_win64.rs
+++ b/src/librustc_trans/cabi_x86_win64.rs
@@ -18,6 +18,7 @@ pub fn compute_abi_info(fty: &mut FnType) {
     let fixup = |a: &mut ArgType| {
         match a.layout.abi {
             layout::Abi::Uninhabited => {}
+            layout::Abi::ScalarPair(..) |
             layout::Abi::Aggregate { .. } => {
                 match a.layout.size.bits() {
                     8 => a.cast_to(Reg::i8()),
diff --git a/src/librustc_trans/common.rs b/src/librustc_trans/common.rs
index 03ae58fd941..8a2c1ed2dc2 100644
--- a/src/librustc_trans/common.rs
+++ b/src/librustc_trans/common.rs
@@ -232,16 +232,9 @@ pub fn C_str_slice(cx: &CrateContext, s: InternedString) -> ValueRef {
 }
 
 pub fn C_fat_ptr(cx: &CrateContext, ptr: ValueRef, meta: ValueRef) -> ValueRef {
-    let empty = C_array(Type::i8(cx), &[]);
     assert_eq!(abi::FAT_PTR_ADDR, 0);
     assert_eq!(abi::FAT_PTR_EXTRA, 1);
-    C_struct(cx, &[
-        empty,
-        ptr,
-        empty,
-        meta,
-        empty
-    ], false)
+    C_struct(cx, &[ptr, meta], false)
 }
 
 pub fn C_struct(cx: &CrateContext, elts: &[ValueRef], packed: bool) -> ValueRef {
diff --git a/src/librustc_trans/context.rs b/src/librustc_trans/context.rs
index d768b14a82e..b2bb605d01b 100644
--- a/src/librustc_trans/context.rs
+++ b/src/librustc_trans/context.rs
@@ -31,7 +31,7 @@ use rustc::middle::trans::Stats;
 use rustc_data_structures::stable_hasher::StableHashingContextProvider;
 use rustc::session::config::{self, NoDebugInfo};
 use rustc::session::Session;
-use rustc::ty::layout::{LayoutError, LayoutOf, TyLayout};
+use rustc::ty::layout::{LayoutError, LayoutOf, Size, TyLayout};
 use rustc::ty::{self, Ty, TyCtxt};
 use rustc::util::nodemap::FxHashMap;
 use rustc_trans_utils;
@@ -103,7 +103,7 @@ pub struct LocalCrateContext<'a, 'tcx: 'a> {
 
     lltypes: RefCell<FxHashMap<(Ty<'tcx>, Option<usize>), Type>>,
     scalar_lltypes: RefCell<FxHashMap<Ty<'tcx>, Type>>,
-    pointee_infos: RefCell<FxHashMap<Ty<'tcx>, Option<PointeeInfo>>>,
+    pointee_infos: RefCell<FxHashMap<(Ty<'tcx>, Size), Option<PointeeInfo>>>,
     isize_ty: Type,
 
     dbg_cx: Option<debuginfo::CrateDebugContext<'tcx>>,
@@ -516,7 +516,8 @@ impl<'b, 'tcx> CrateContext<'b, 'tcx> {
         &self.local().scalar_lltypes
     }
 
-    pub fn pointee_infos<'a>(&'a self) -> &'a RefCell<FxHashMap<Ty<'tcx>, Option<PointeeInfo>>> {
+    pub fn pointee_infos<'a>(&'a self)
+                             -> &'a RefCell<FxHashMap<(Ty<'tcx>, Size), Option<PointeeInfo>>> {
         &self.local().pointee_infos
     }
 
diff --git a/src/librustc_trans/mir/analyze.rs b/src/librustc_trans/mir/analyze.rs
index bf822249a64..3129ed028d4 100644
--- a/src/librustc_trans/mir/analyze.rs
+++ b/src/librustc_trans/mir/analyze.rs
@@ -35,7 +35,7 @@ pub fn lvalue_locals<'a, 'tcx>(mircx: &MirContext<'a, 'tcx>) -> BitVector {
         if layout.is_llvm_immediate() {
             // These sorts of types are immediates that we can store
             // in an ValueRef without an alloca.
-        } else if layout.is_llvm_scalar_pair(mircx.ccx) {
+        } else if layout.is_llvm_scalar_pair() {
             // We allow pairs and uses of any of their 2 fields.
         } else {
             // These sorts of types require an alloca. Note that
@@ -146,7 +146,7 @@ impl<'mir, 'a, 'tcx> Visitor<'tcx> for LocalAnalyzer<'mir, 'a, 'tcx> {
 
                         let ty = self.cx.monomorphize(&ty.to_ty(self.cx.ccx.tcx()));
                         let layout = self.cx.ccx.layout_of(ty);
-                        if layout.is_llvm_scalar_pair(self.cx.ccx) {
+                        if layout.is_llvm_scalar_pair() {
                             return;
                         }
                     }
diff --git a/src/librustc_trans/mir/constant.rs b/src/librustc_trans/mir/constant.rs
index 3196300a706..318e36dc71a 100644
--- a/src/librustc_trans/mir/constant.rs
+++ b/src/librustc_trans/mir/constant.rs
@@ -117,7 +117,12 @@ impl<'a, 'tcx> Const<'tcx> {
     }
 
     fn get_field(&self, ccx: &CrateContext<'a, 'tcx>, i: usize) -> ValueRef {
-        const_get_elt(self.llval, ccx.layout_of(self.ty).llvm_field_index(i))
+        let layout = ccx.layout_of(self.ty);
+        if let layout::Abi::ScalarPair(..) = layout.abi {
+            const_get_elt(self.llval, i as u64)
+        } else {
+            const_get_elt(self.llval, layout.llvm_field_index(i))
+        }
     }
 
     fn get_pair(&self, ccx: &CrateContext<'a, 'tcx>) -> (ValueRef, ValueRef) {
@@ -143,7 +148,7 @@ impl<'a, 'tcx> Const<'tcx> {
         let llty = layout.immediate_llvm_type(ccx);
         let llvalty = val_ty(self.llval);
 
-        let val = if llty == llvalty && layout.is_llvm_scalar_pair(ccx) {
+        let val = if llty == llvalty && layout.is_llvm_scalar_pair() {
             let (a, b) = self.get_pair(ccx);
             OperandValue::Pair(a, b)
         } else if llty == llvalty && layout.is_llvm_immediate() {
@@ -1174,6 +1179,14 @@ fn build_const_struct<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>,
                                 -> Const<'tcx> {
     assert_eq!(vals.len(), layout.fields.count());
 
+    if let layout::Abi::ScalarPair(..) = layout.abi {
+        assert_eq!(vals.len(), 2);
+        return Const::new(C_struct(ccx, &[
+            vals[0].llval,
+            vals[1].llval,
+        ], false), layout.ty);
+    }
+
     // offset of current value
     let mut offset = Size::from_bytes(0);
     let mut cfields = Vec::new();
diff --git a/src/librustc_trans/mir/lvalue.rs b/src/librustc_trans/mir/lvalue.rs
index 8340d865eb1..ff0b4482678 100644
--- a/src/librustc_trans/mir/lvalue.rs
+++ b/src/librustc_trans/mir/lvalue.rs
@@ -175,10 +175,13 @@ impl<'a, 'tcx> LvalueRef<'tcx> {
                 load
             };
             OperandValue::Immediate(base::to_immediate(bcx, llval, self.layout))
-        } else if self.layout.is_llvm_scalar_pair(bcx.ccx) {
-            OperandValue::Pair(
-                self.project_field(bcx, 0).load(bcx).immediate(),
-                self.project_field(bcx, 1).load(bcx).immediate())
+        } else if self.layout.is_llvm_scalar_pair() {
+            let load = |i| {
+                let x = self.project_field(bcx, i).load(bcx).immediate();
+                // HACK(eddyb) have to bitcast pointers until LLVM removes pointee types.
+                bcx.bitcast(x, self.layout.scalar_pair_element_llvm_type(bcx.ccx, i))
+            };
+            OperandValue::Pair(load(0), load(1))
         } else {
             OperandValue::Ref(self.llval, self.alignment)
         };
@@ -190,17 +193,23 @@ impl<'a, 'tcx> LvalueRef<'tcx> {
     pub fn project_field(self, bcx: &Builder<'a, 'tcx>, ix: usize) -> LvalueRef<'tcx> {
         let ccx = bcx.ccx;
         let field = self.layout.field(ccx, ix);
-        let offset = self.layout.fields.offset(ix).bytes();
+        let offset = self.layout.fields.offset(ix);
         let alignment = self.alignment | Alignment::from(self.layout);
 
         let simple = || {
+            // Unions and newtypes only use an offset of 0.
+            let llval = if offset.bytes() == 0 {
+                self.llval
+            } else if let layout::Abi::ScalarPair(ref a, ref b) = self.layout.abi {
+                // Offsets have to match either first or second field.
+                assert_eq!(offset, a.value.size(ccx).abi_align(b.value.align(ccx)));
+                bcx.struct_gep(self.llval, 1)
+            } else {
+                bcx.struct_gep(self.llval, self.layout.llvm_field_index(ix))
+            };
             LvalueRef {
-                // Unions and newtypes only use an offset of 0.
-                llval: if offset == 0 {
-                    bcx.pointercast(self.llval, field.llvm_type(ccx).ptr_to())
-                } else {
-                    bcx.struct_gep(self.llval, self.layout.llvm_field_index(ix))
-                },
+                // HACK(eddyb) have to bitcast pointers until LLVM removes pointee types.
+                llval: bcx.pointercast(llval, field.llvm_type(ccx).ptr_to()),
                 llextra: if ccx.shared().type_has_metadata(field.ty) {
                     self.llextra
                 } else {
@@ -249,7 +258,7 @@ impl<'a, 'tcx> LvalueRef<'tcx> {
 
         let meta = self.llextra;
 
-        let unaligned_offset = C_usize(ccx, offset);
+        let unaligned_offset = C_usize(ccx, offset.bytes());
 
         // Get the alignment of the field
         let (_, align) = glue::size_and_align_of_dst(bcx, field.ty, meta);
diff --git a/src/librustc_trans/mir/operand.rs b/src/librustc_trans/mir/operand.rs
index 3e7aa9d0db5..b9d4148acf6 100644
--- a/src/librustc_trans/mir/operand.rs
+++ b/src/librustc_trans/mir/operand.rs
@@ -123,11 +123,8 @@ impl<'a, 'tcx> OperandRef<'tcx> {
                    self, llty);
             // Reconstruct the immediate aggregate.
             let mut llpair = C_undef(llty);
-            let elems = [a, b];
-            for i in 0..2 {
-                let elem = base::from_immediate(bcx, elems[i]);
-                llpair = bcx.insert_value(llpair, elem, self.layout.llvm_field_index(i));
-            }
+            llpair = bcx.insert_value(llpair, a, 0);
+            llpair = bcx.insert_value(llpair, b, 1);
             llpair
         } else {
             self.immediate()
@@ -139,18 +136,13 @@ impl<'a, 'tcx> OperandRef<'tcx> {
                                          llval: ValueRef,
                                          layout: TyLayout<'tcx>)
                                          -> OperandRef<'tcx> {
-        let val = if layout.is_llvm_scalar_pair(bcx.ccx) {
+        let val = if layout.is_llvm_scalar_pair() {
             debug!("Operand::from_immediate_or_packed_pair: unpacking {:?} @ {:?}",
                     llval, layout);
 
             // Deconstruct the immediate aggregate.
-            let a = bcx.extract_value(llval, layout.llvm_field_index(0));
-            let a = base::to_immediate(bcx, a, layout.field(bcx.ccx, 0));
-
-            let b = bcx.extract_value(llval, layout.llvm_field_index(1));
-            let b = base::to_immediate(bcx, b, layout.field(bcx.ccx, 1));
-
-            OperandValue::Pair(a, b)
+            OperandValue::Pair(bcx.extract_value(llval, 0),
+                               bcx.extract_value(llval, 1))
         } else {
             OperandValue::Immediate(llval)
         };
@@ -175,8 +167,11 @@ impl<'a, 'tcx> OperandValue {
             }
             OperandValue::Pair(a, b) => {
                 for (i, &x) in [a, b].iter().enumerate() {
-                    OperandValue::Immediate(x)
-                        .store(bcx, dest.project_field(bcx, i));
+                    let field = dest.project_field(bcx, i);
+                    // HACK(eddyb) have to bitcast pointers until LLVM removes pointee types.
+                    let x = bcx.bitcast(x, field.layout.immediate_llvm_type(bcx.ccx));
+                    bcx.store(base::from_immediate(bcx, x),
+                              field.llval, field.alignment.non_abi());
                 }
             }
         }
@@ -214,10 +209,15 @@ impl<'a, 'tcx> MirContext<'a, 'tcx> {
                     match (o.val, &proj.elem) {
                         (OperandValue::Pair(a, b),
                          &mir::ProjectionElem::Field(ref f, ty)) => {
+                            let layout = bcx.ccx.layout_of(self.monomorphize(&ty));
                             let llval = [a, b][f.index()];
+                            // HACK(eddyb) have to bitcast pointers
+                            // until LLVM removes pointee types.
+                            let llval = bcx.bitcast(llval,
+                                layout.immediate_llvm_type(bcx.ccx));
                             return OperandRef {
                                 val: OperandValue::Immediate(llval),
-                                layout: bcx.ccx.layout_of(self.monomorphize(&ty))
+                                layout
                             };
                         }
                         _ => {}
diff --git a/src/librustc_trans/type_of.rs b/src/librustc_trans/type_of.rs
index 6da6f1ebaf0..d62e2ac1552 100644
--- a/src/librustc_trans/type_of.rs
+++ b/src/librustc_trans/type_of.rs
@@ -29,6 +29,12 @@ fn uncached_llvm_type<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>,
             return Type::vector(&layout.field(ccx, 0).llvm_type(ccx),
                                 layout.fields.count() as u64);
         }
+        layout::Abi::ScalarPair(..) => {
+            return Type::struct_(ccx, &[
+                layout.scalar_pair_element_llvm_type(ccx, 0),
+                layout.scalar_pair_element_llvm_type(ccx, 1),
+            ], false);
+        }
         layout::Abi::Uninhabited |
         layout::Abi::Aggregate { .. } => {}
     }
@@ -174,12 +180,15 @@ pub struct PointeeInfo {
 
 pub trait LayoutLlvmExt<'tcx> {
     fn is_llvm_immediate(&self) -> bool;
-    fn is_llvm_scalar_pair<'a>(&self, ccx: &CrateContext<'a, 'tcx>) -> bool;
+    fn is_llvm_scalar_pair<'a>(&self) -> bool;
     fn llvm_type<'a>(&self, ccx: &CrateContext<'a, 'tcx>) -> Type;
     fn immediate_llvm_type<'a>(&self, ccx: &CrateContext<'a, 'tcx>) -> Type;
+    fn scalar_pair_element_llvm_type<'a>(&self, ccx: &CrateContext<'a, 'tcx>,
+                                         index: usize) -> Type;
     fn over_align(&self) -> Option<Align>;
     fn llvm_field_index(&self, index: usize) -> u64;
-    fn pointee_info<'a>(&self, ccx: &CrateContext<'a, 'tcx>) -> Option<PointeeInfo>;
+    fn pointee_info_at<'a>(&self, ccx: &CrateContext<'a, 'tcx>, offset: Size)
+                           -> Option<PointeeInfo>;
 }
 
 impl<'tcx> LayoutLlvmExt<'tcx> for TyLayout<'tcx> {
@@ -188,26 +197,18 @@ impl<'tcx> LayoutLlvmExt<'tcx> for TyLayout<'tcx> {
             layout::Abi::Uninhabited |
             layout::Abi::Scalar(_) |
             layout::Abi::Vector => true,
-
+            layout::Abi::ScalarPair(..) => false,
             layout::Abi::Aggregate { .. } => self.is_zst()
         }
     }
 
-    fn is_llvm_scalar_pair<'a>(&self, ccx: &CrateContext<'a, 'tcx>) -> bool {
-        match self.fields {
-            layout::FieldPlacement::Arbitrary { .. } => {
-                // There must be only 2 fields.
-                if self.fields.count() != 2 {
-                    return false;
-                }
-
-                // The two fields must be both scalars.
-                match (&self.field(ccx, 0).abi, &self.field(ccx, 1).abi) {
-                    (&layout::Abi::Scalar(_), &layout::Abi::Scalar(_)) => true,
-                    _ => false
-                }
-            }
-            _ => false
+    fn is_llvm_scalar_pair<'a>(&self) -> bool {
+        match self.abi {
+            layout::Abi::ScalarPair(..) => true,
+            layout::Abi::Uninhabited |
+            layout::Abi::Scalar(_) |
+            layout::Abi::Vector |
+            layout::Abi::Aggregate { .. } => false
         }
     }
 
@@ -248,7 +249,7 @@ impl<'tcx> LayoutLlvmExt<'tcx> for TyLayout<'tcx> {
                         }
                         _ => {
                             // If we know the alignment, pick something better than i8.
-                            if let Some(pointee) = self.pointee_info(ccx) {
+                            if let Some(pointee) = self.pointee_info_at(ccx, Size::from_bytes(0)) {
                                 Type::pointee_for_abi_align(ccx, pointee.align)
                             } else {
                                 Type::i8(ccx)
@@ -310,6 +311,59 @@ impl<'tcx> LayoutLlvmExt<'tcx> for TyLayout<'tcx> {
         self.llvm_type(ccx)
     }
 
+    fn scalar_pair_element_llvm_type<'a>(&self, ccx: &CrateContext<'a, 'tcx>,
+                                         index: usize) -> Type {
+        // HACK(eddyb) special-case fat pointers until LLVM removes
+        // pointee types, to avoid bitcasting every `OperandRef::deref`.
+        match self.ty.sty {
+            ty::TyRef(..) |
+            ty::TyRawPtr(_) => {
+                return self.field(ccx, index).llvm_type(ccx);
+            }
+            ty::TyAdt(def, _) if def.is_box() => {
+                return self.field(ccx, index).llvm_type(ccx);
+            }
+            _ => {}
+        }
+
+        let (a, b) = match self.abi {
+            layout::Abi::ScalarPair(ref a, ref b) => (a, b),
+            _ => bug!("TyLayout::scalar_pair_element_llty({:?}): not applicable", self)
+        };
+        let scalar = [a, b][index];
+
+        // Make sure to return the same type `immediate_llvm_type` would,
+        // to avoid dealing with two types and the associated conversions.
+        // This means that `(bool, bool)` is represented as `{i1, i1}`,
+        // both in memory and as an immediate, while `bool` is typically
+        // `i8` in memory and only `i1` when immediate. While we need to
+        // load/store `bool` as `i8` to avoid crippling LLVM optimizations,
+        // `i1` in a LLVM aggregate is valid and mostly equivalent to `i8`.
+        if scalar.is_bool() {
+            return Type::i1(ccx);
+        }
+
+        match scalar.value {
+            layout::Int(i, _) => Type::from_integer(ccx, i),
+            layout::F32 => Type::f32(ccx),
+            layout::F64 => Type::f64(ccx),
+            layout::Pointer => {
+                // If we know the alignment, pick something better than i8.
+                let offset = if index == 0 {
+                    Size::from_bytes(0)
+                } else {
+                    a.value.size(ccx).abi_align(b.value.align(ccx))
+                };
+                let pointee = if let Some(pointee) = self.pointee_info_at(ccx, offset) {
+                    Type::pointee_for_abi_align(ccx, pointee.align)
+                } else {
+                    Type::i8(ccx)
+                };
+                pointee.ptr_to()
+            }
+        }
+    }
+
     fn over_align(&self) -> Option<Align> {
         if self.align != self.primitive_align {
             Some(self.align)
@@ -319,8 +373,12 @@ impl<'tcx> LayoutLlvmExt<'tcx> for TyLayout<'tcx> {
     }
 
     fn llvm_field_index(&self, index: usize) -> u64 {
-        if let layout::Abi::Scalar(_) = self.abi {
-            bug!("TyLayout::llvm_field_index({:?}): not applicable", self);
+        match self.abi {
+            layout::Abi::Scalar(_) |
+            layout::Abi::ScalarPair(..) => {
+                bug!("TyLayout::llvm_field_index({:?}): not applicable", self)
+            }
+            _ => {}
         }
         match self.fields {
             layout::FieldPlacement::Union(_) => {
@@ -337,20 +395,15 @@ impl<'tcx> LayoutLlvmExt<'tcx> for TyLayout<'tcx> {
         }
     }
 
-    fn pointee_info<'a>(&self, ccx: &CrateContext<'a, 'tcx>) -> Option<PointeeInfo> {
-        // We only handle thin pointers here.
-        match self.abi {
-            layout::Abi::Scalar(layout::Scalar { value: layout::Pointer, .. }) => {}
-            _ => return None
-        }
-
-        if let Some(&pointee) = ccx.pointee_infos().borrow().get(&self.ty) {
+    fn pointee_info_at<'a>(&self, ccx: &CrateContext<'a, 'tcx>, offset: Size)
+                           -> Option<PointeeInfo> {
+        if let Some(&pointee) = ccx.pointee_infos().borrow().get(&(self.ty, offset)) {
             return pointee;
         }
 
         let mut result = None;
         match self.ty.sty {
-            ty::TyRawPtr(mt) => {
+            ty::TyRawPtr(mt) if offset.bytes() == 0 => {
                 let (size, align) = ccx.size_and_align_of(mt.ty);
                 result = Some(PointeeInfo {
                     size,
@@ -359,7 +412,7 @@ impl<'tcx> LayoutLlvmExt<'tcx> for TyLayout<'tcx> {
                 });
             }
 
-            ty::TyRef(_, mt) => {
+            ty::TyRef(_, mt) if offset.bytes() == 0 => {
                 let (size, align) = ccx.size_and_align_of(mt.ty);
 
                 let kind = match mt.mutbl {
@@ -385,7 +438,7 @@ impl<'tcx> LayoutLlvmExt<'tcx> for TyLayout<'tcx> {
                 });
             }
 
-            ty::TyAdt(def, _) if def.is_box() => {
+            ty::TyAdt(def, _) if def.is_box() && offset.bytes() == 0 => {
                 let (size, align) = ccx.size_and_align_of(self.ty.boxed_ty());
                 result = Some(PointeeInfo {
                     size,
@@ -408,7 +461,7 @@ impl<'tcx> LayoutLlvmExt<'tcx> for TyLayout<'tcx> {
                         // to work as long as we don't start using more
                         // niches than just null (e.g. the first page
                         // of the address space, or unaligned pointers).
-                        if self.fields.offset(0).bytes() == 0 {
+                        if self.fields.offset(0) == offset {
                             Some(self.for_variant(ccx, dataful_variant))
                         } else {
                             None
@@ -425,12 +478,16 @@ impl<'tcx> LayoutLlvmExt<'tcx> for TyLayout<'tcx> {
                 }
 
                 if let Some(variant) = data_variant {
+                    let ptr_end = offset + layout::Pointer.size(ccx);
                     for i in 0..variant.fields.count() {
-                        let field = variant.field(ccx, i);
-                        if field.size == self.size {
-                            // We found the pointer field, use its information.
-                            result = field.pointee_info(ccx);
-                            break;
+                        let field_start = variant.fields.offset(i);
+                        if field_start <= offset {
+                            let field = variant.field(ccx, i);
+                            if ptr_end <= field_start + field.size {
+                                // We found the right field, look inside it.
+                                result = field.pointee_info_at(ccx, offset - field_start);
+                                break;
+                            }
                         }
                     }
                 }
@@ -447,7 +504,7 @@ impl<'tcx> LayoutLlvmExt<'tcx> for TyLayout<'tcx> {
             }
         }
 
-        ccx.pointee_infos().borrow_mut().insert(self.ty, result);
+        ccx.pointee_infos().borrow_mut().insert((self.ty, offset), result);
         result
     }
 }
diff --git a/src/test/codegen/adjustments.rs b/src/test/codegen/adjustments.rs
index 525a1f5310c..2b35d454739 100644
--- a/src/test/codegen/adjustments.rs
+++ b/src/test/codegen/adjustments.rs
@@ -24,9 +24,9 @@ pub fn helper(_: usize) {
 pub fn no_op_slice_adjustment(x: &[u8]) -> &[u8] {
     // We used to generate an extra alloca and memcpy for the block's trailing expression value, so
     // check that we copy directly to the return value slot
-// CHECK: %0 = insertvalue { [0 x i8], [0 x i8]*, [0 x i8], [[USIZE]], [0 x i8] } undef, [0 x i8]* %x.0, 1
-// CHECK: %1 = insertvalue { [0 x i8], [0 x i8]*, [0 x i8], [[USIZE]], [0 x i8] } %0, [[USIZE]] %x.1, 3
-// CHECK: ret { [0 x i8], [0 x i8]*, [0 x i8], [[USIZE]], [0 x i8] } %1
+// CHECK: %0 = insertvalue { [0 x i8]*, [[USIZE]] } undef, [0 x i8]* %x.0, 0
+// CHECK: %1 = insertvalue { [0 x i8]*, [[USIZE]] } %0, [[USIZE]] %x.1, 1
+// CHECK: ret { [0 x i8]*, [[USIZE]] } %1
     { x }
 }
 
diff --git a/src/test/codegen/function-arguments.rs b/src/test/codegen/function-arguments.rs
index 6cb1972afa5..428cbdddb22 100644
--- a/src/test/codegen/function-arguments.rs
+++ b/src/test/codegen/function-arguments.rs
@@ -133,7 +133,7 @@ pub fn trait_borrow(_: &Drop) {
 pub fn trait_box(_: Box<Drop>) {
 }
 
-// CHECK: { [0 x i8], [0 x i16]*, [0 x i8], [[USIZE]], [0 x i8] } @return_slice([0 x i16]* noalias nonnull readonly %x.0, [[USIZE]] %x.1)
+// CHECK: { [0 x i16]*, [[USIZE]] } @return_slice([0 x i16]* noalias nonnull readonly %x.0, [[USIZE]] %x.1)
 #[no_mangle]
 pub fn return_slice(x: &[u16]) -> &[u16] {
   x
diff --git a/src/test/codegen/packed.rs b/src/test/codegen/packed.rs
index 87cf042f27e..64e842b026e 100644
--- a/src/test/codegen/packed.rs
+++ b/src/test/codegen/packed.rs
@@ -54,9 +54,6 @@ pub struct PackedPair(u8, u32);
 // CHECK-LABEL: @pkd_pair
 #[no_mangle]
 pub fn pkd_pair(pair1: &mut PackedPair, pair2: &mut PackedPair) {
-    // CHECK: [[V1:%[a-z0-9]+]] = load i8, i8* %{{.*}}, align 1
-    // CHECK: [[V2:%[a-z0-9]+]] = load i32, i32* %{{.*}}, align 1
-    // CHECK: store i8 [[V1]], i8* {{.*}}, align 1
-    // CHECK: store i32 [[V2]], i32* {{.*}}, align 1
+// CHECK: call void @llvm.memcpy.{{.*}}(i8* %{{.*}}, i8* %{{.*}}, i{{[0-9]+}} 5, i32 1, i1 false)
     *pair2 = *pair1;
 }
diff --git a/src/test/codegen/refs.rs b/src/test/codegen/refs.rs
index 2ab64fffa3b..0c084131ea3 100644
--- a/src/test/codegen/refs.rs
+++ b/src/test/codegen/refs.rs
@@ -24,9 +24,9 @@ pub fn helper(_: usize) {
 pub fn ref_dst(s: &[u8]) {
     // We used to generate an extra alloca and memcpy to ref the dst, so check that we copy
     // directly to the alloca for "x"
-// CHECK: [[X0:%[0-9]+]] = bitcast { [0 x i8], [0 x i8]*, [0 x i8], [[USIZE]], [0 x i8] }* %x to [0 x i8]**
+// CHECK: [[X0:%[0-9]+]] = bitcast { [0 x i8]*, [[USIZE]] }* %x to [0 x i8]**
 // CHECK: store [0 x i8]* %s.0, [0 x i8]** [[X0]]
-// CHECK: [[X1:%[0-9]+]] = getelementptr {{.*}} { [0 x i8], [0 x i8]*, [0 x i8], [[USIZE]], [0 x i8] }* %x, i32 0, i32 3
+// CHECK: [[X1:%[0-9]+]] = getelementptr {{.*}} { [0 x i8]*, [[USIZE]] }* %x, i32 0, i32 1
 // CHECK: store [[USIZE]] %s.1, [[USIZE]]* [[X1]]
 
     let x = &*s;