diff --git a/src/librustc/session/config.rs b/src/librustc/session/config.rs
index ef825a6854cec..b9a974045bced 100644
--- a/src/librustc/session/config.rs
+++ b/src/librustc/session/config.rs
@@ -643,6 +643,8 @@ macro_rules! options {
             Some("one of: `address`, `leak`, `memory` or `thread`");
         pub const parse_linker_flavor: Option<&'static str> =
             Some(::rustc_back::LinkerFlavor::one_of());
+        pub const parse_optimization_fuel: Option<&'static str> =
+            Some("crate=integer");
     }
 
     #[allow(dead_code)]
@@ -787,6 +789,21 @@ macro_rules! options {
             }
             true
         }
+
+        fn parse_optimization_fuel(slot: &mut Option<(String, u64)>, v: Option<&str>) -> bool {
+            match v {
+                None => false,
+                Some(s) => {
+                    let parts = s.split('=').collect::<Vec<_>>();
+                    if parts.len() != 2 { return false; }
+                    let crate_name = parts[0].to_string();
+                    let fuel = parts[1].parse::<u64>();
+                    if fuel.is_err() { return false; }
+                    *slot = Some((crate_name, fuel.unwrap()));
+                    true
+                }
+            }
+        }
     }
 ) }
 
@@ -991,6 +1008,10 @@ options! {DebuggingOptions, DebuggingSetter, basic_debugging_options,
                                    "Use a sanitizer"),
     linker_flavor: Option<LinkerFlavor> = (None, parse_linker_flavor, [UNTRACKED],
                                            "Linker flavor"),
+    fuel: Option<(String, u64)> = (None, parse_optimization_fuel, [TRACKED],
+        "Set the optimization fuel quota for a crate."),
+    print_fuel: Option<String> = (None, parse_opt_string, [TRACKED],
+        "Make Rustc print the total optimization fuel used by a crate."),
 }
 
 pub fn default_lib_output() -> CrateType {
@@ -1784,11 +1805,13 @@ mod dep_tracking {
 
     impl_dep_tracking_hash_via_hash!(bool);
     impl_dep_tracking_hash_via_hash!(usize);
+    impl_dep_tracking_hash_via_hash!(u64);
     impl_dep_tracking_hash_via_hash!(String);
     impl_dep_tracking_hash_via_hash!(lint::Level);
     impl_dep_tracking_hash_via_hash!(Option<bool>);
     impl_dep_tracking_hash_via_hash!(Option<usize>);
     impl_dep_tracking_hash_via_hash!(Option<String>);
+    impl_dep_tracking_hash_via_hash!(Option<(String, u64)>);
     impl_dep_tracking_hash_via_hash!(Option<PanicStrategy>);
     impl_dep_tracking_hash_via_hash!(Option<lint::Level>);
     impl_dep_tracking_hash_via_hash!(Option<PathBuf>);
@@ -1810,6 +1833,7 @@ mod dep_tracking {
     impl_dep_tracking_hash_for_sortable_vec_of!((String, lint::Level));
     impl_dep_tracking_hash_for_sortable_vec_of!((String, Option<String>,
                                                  Option<cstore::NativeLibraryKind>));
+    impl_dep_tracking_hash_for_sortable_vec_of!((String, u64));
     impl DepTrackingHash for SearchPaths {
         fn hash(&self, hasher: &mut DefaultHasher, _: ErrorOutputType) {
             let mut elems: Vec<_> = self
diff --git a/src/librustc/session/mod.rs b/src/librustc/session/mod.rs
index 70b2809ccbed2..039db3d9ee911 100644
--- a/src/librustc/session/mod.rs
+++ b/src/librustc/session/mod.rs
@@ -123,6 +123,20 @@ pub struct Session {
     pub code_stats: RefCell<CodeStats>,
 
     next_node_id: Cell<ast::NodeId>,
+
+    /// If -zfuel=crate=n is specified, Some(crate).
+    optimization_fuel_crate: Option<String>,
+    /// If -zfuel=crate=n is specified, initially set to n. Otherwise 0.
+    optimization_fuel_limit: Cell<u64>,
+    /// We're rejecting all further optimizations.
+    out_of_fuel: Cell<bool>,
+
+    // The next two are public because the driver needs to read them.
+
+    /// If -zprint-fuel=crate, Some(crate).
+    pub print_fuel_crate: Option<String>,
+    /// Always set to zero and incremented so that we can print fuel expended by a crate.
+    pub print_fuel: Cell<u64>,
 }
 
 pub struct PerfStats {
@@ -507,6 +521,32 @@ impl Session {
         println!("Total time spent decoding DefPath tables:      {}",
                  duration_to_secs_str(self.perf_stats.decode_def_path_tables_time.get()));
     }
+
+    /// We want to know if we're allowed to do an optimization for crate foo from -z fuel=foo=n.
+    /// This expends fuel if applicable, and records fuel if applicable.
+    pub fn consider_optimizing<T: Fn() -> String>(&self, crate_name: &str, msg: T) -> bool {
+        let mut ret = true;
+        match self.optimization_fuel_crate {
+            Some(ref c) if c == crate_name => {
+                let fuel = self.optimization_fuel_limit.get();
+                ret = fuel != 0;
+                if fuel == 0 && !self.out_of_fuel.get() {
+                    println!("optimization-fuel-exhausted: {}", msg());
+                    self.out_of_fuel.set(true);
+                } else if fuel > 0 {
+                    self.optimization_fuel_limit.set(fuel-1);
+                }
+            }
+            _ => {}
+        }
+        match self.print_fuel_crate {
+            Some(ref c) if c == crate_name=> {
+                self.print_fuel.set(self.print_fuel.get()+1);
+            },
+            _ => {}
+        }
+        ret
+    }
 }
 
 pub fn build_session(sopts: config::Options,
@@ -602,6 +642,12 @@ pub fn build_session_(sopts: config::Options,
         }
     );
 
+    let optimization_fuel_crate = sopts.debugging_opts.fuel.as_ref().map(|i| i.0.clone());
+    let optimization_fuel_limit = Cell::new(sopts.debugging_opts.fuel.as_ref()
+        .map(|i| i.1).unwrap_or(0));
+    let print_fuel_crate = sopts.debugging_opts.print_fuel.clone();
+    let print_fuel = Cell::new(0);
+
     let sess = Session {
         dep_graph: dep_graph.clone(),
         target: target_cfg,
@@ -643,6 +689,11 @@ pub fn build_session_(sopts: config::Options,
             decode_def_path_tables_time: Cell::new(Duration::from_secs(0)),
         },
         code_stats: RefCell::new(CodeStats::new()),
+        optimization_fuel_crate: optimization_fuel_crate,
+        optimization_fuel_limit: optimization_fuel_limit,
+        print_fuel_crate: print_fuel_crate,
+        print_fuel: print_fuel,
+        out_of_fuel: Cell::new(false),
     };
 
     init_llvm(&sess);
diff --git a/src/librustc/ty/context.rs b/src/librustc/ty/context.rs
index da56514ea82fb..8b7438c0bfad2 100644
--- a/src/librustc/ty/context.rs
+++ b/src/librustc/ty/context.rs
@@ -732,6 +732,11 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
             ast_ty_to_ty_cache: RefCell::new(NodeMap()),
        }, f)
     }
+
+    pub fn consider_optimizing<T: Fn() -> String>(&self, msg: T) -> bool {
+        let cname = self.crate_name(LOCAL_CRATE).as_str();
+        self.sess.consider_optimizing(&cname, msg)
+    }
 }
 
 impl<'gcx: 'tcx, 'tcx> GlobalCtxt<'gcx> {
diff --git a/src/librustc/ty/layout.rs b/src/librustc/ty/layout.rs
index 54e5de3909086..d7a4b3fda63bb 100644
--- a/src/librustc/ty/layout.rs
+++ b/src/librustc/ty/layout.rs
@@ -580,7 +580,6 @@ enum StructKind {
 }
 
 impl<'a, 'gcx, 'tcx> Struct {
-    // FIXME(camlorn): reprs need a better representation to deal with multiple reprs on one type.
     fn new(dl: &TargetDataLayout, fields: &Vec<&'a Layout>,
                   repr: &ReprOptions, kind: StructKind,
                   scapegoat: Ty<'gcx>) -> Result<Struct, LayoutError<'gcx>> {
@@ -598,12 +597,8 @@ impl<'a, 'gcx, 'tcx> Struct {
         // Neither do  1-member and 2-member structs.
         // In addition, code in trans assume that 2-element structs can become pairs.
         // It's easier to just short-circuit here.
-        let mut can_optimize = (fields.len() > 2 || StructKind::EnumVariant == kind)
-            && ! (repr.c || repr.packed);
-
-        // Disable field reordering until we can decide what to do.
-        // The odd pattern here avoids a warning about the value never being read.
-        if can_optimize { can_optimize = false; }
+        let can_optimize = (fields.len() > 2 || StructKind::EnumVariant == kind)
+            && !(repr.c || repr.packed || repr.linear || repr.simd);
 
         let (optimize, sort_ascending) = match kind {
             StructKind::AlwaysSizedUnivariant => (can_optimize, false),
diff --git a/src/librustc/ty/mod.rs b/src/librustc/ty/mod.rs
index 292e30e3d41f1..a2c356c20db09 100644
--- a/src/librustc/ty/mod.rs
+++ b/src/librustc/ty/mod.rs
@@ -1411,13 +1411,16 @@ pub struct ReprOptions {
     pub packed: bool,
     pub simd: bool,
     pub int: Option<attr::IntType>,
+    // Internal only for now. If true, don't reorder fields.
+    pub linear: bool,
 }
 
 impl_stable_hash_for!(struct ReprOptions {
     c,
     packed,
     simd,
-    int
+    int,
+    linear
 });
 
 impl ReprOptions {
@@ -1440,6 +1443,9 @@ impl ReprOptions {
             ret.simd = true;
         }
 
+        // This is here instead of layout because the choice must make it into metadata.
+        ret.linear = !tcx.consider_optimizing(|| format!("Reorder fields of {:?}",
+            tcx.item_path_str(did)));
         ret
     }
 
diff --git a/src/librustc_driver/lib.rs b/src/librustc_driver/lib.rs
index c90dde3a5f6e0..1a892b73aa5d7 100644
--- a/src/librustc_driver/lib.rs
+++ b/src/librustc_driver/lib.rs
@@ -517,6 +517,16 @@ impl<'a> CompilerCalls<'a> for RustcDefaultCalls {
             control.make_glob_map = resolve::MakeGlobMap::Yes;
         }
 
+        if sess.print_fuel_crate.is_some() {
+            let old_callback = control.compilation_done.callback;
+            control.compilation_done.callback = box move |state| {
+                old_callback(state);
+                let sess = state.session;
+                println!("Fuel used by {}: {}",
+                    sess.print_fuel_crate.as_ref().unwrap(),
+                    sess.print_fuel.get());
+            }
+        }
         control
     }
 }
diff --git a/src/librustc_trans/intrinsic.rs b/src/librustc_trans/intrinsic.rs
index 5e7d612d17f82..7cfc28622c443 100644
--- a/src/librustc_trans/intrinsic.rs
+++ b/src/librustc_trans/intrinsic.rs
@@ -16,7 +16,7 @@ use llvm;
 use llvm::{ValueRef};
 use abi::{Abi, FnType};
 use adt;
-use mir::lvalue::LvalueRef;
+use mir::lvalue::{LvalueRef, Alignment};
 use base::*;
 use common::*;
 use declare;
@@ -36,8 +36,6 @@ use syntax_pos::Span;
 use std::cmp::Ordering;
 use std::iter;
 
-use mir::lvalue::Alignment;
-
 fn get_simple_intrinsic(ccx: &CrateContext, name: &str) -> Option<ValueRef> {
     let llvm_name = match name {
         "sqrtf32" => "llvm.sqrt.f32",
@@ -622,7 +620,10 @@ pub fn trans_intrinsic_call<'a, 'tcx>(bcx: &Builder<'a, 'tcx>,
 
                     for i in 0..elems.len() {
                         let val = bcx.extract_value(val, i);
-                        bcx.store(val, bcx.struct_gep(llresult, i), None);
+                        let lval = LvalueRef::new_sized_ty(llresult, ret_ty,
+                                                           Alignment::AbiAligned);
+                        let (dest, align) = lval.trans_field_ptr(bcx, i);
+                        bcx.store(val, dest, align.to_align());
                     }
                     C_nil(ccx)
                 }
diff --git a/src/librustc_trans/mir/mod.rs b/src/librustc_trans/mir/mod.rs
index c8d15d28708f4..f4c9a136ace3c 100644
--- a/src/librustc_trans/mir/mod.rs
+++ b/src/librustc_trans/mir/mod.rs
@@ -386,7 +386,7 @@ fn arg_local_refs<'a, 'tcx>(bcx: &Builder<'a, 'tcx>,
 
             let lvalue = LvalueRef::alloca(bcx, arg_ty, &format!("arg{}", arg_index));
             for (i, &tupled_arg_ty) in tupled_arg_tys.iter().enumerate() {
-                let dst = bcx.struct_gep(lvalue.llval, i);
+                let (dst, _) = lvalue.trans_field_ptr(bcx, i);
                 let arg = &mircx.fn_ty.args[idx];
                 idx += 1;
                 if common::type_is_fat_ptr(bcx.ccx, tupled_arg_ty) {
diff --git a/src/test/run-pass/optimization-fuel-0.rs b/src/test/run-pass/optimization-fuel-0.rs
new file mode 100644
index 0000000000000..3832c040108f8
--- /dev/null
+++ b/src/test/run-pass/optimization-fuel-0.rs
@@ -0,0 +1,24 @@
+// Copyright 2012 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#![crate_name="foo"]
+
+use std::mem::size_of;
+
+// compile-flags: -Z fuel=foo=0
+
+struct S1(u8, u16, u8);
+struct S2(u8, u16, u8);
+
+fn main() {
+    assert_eq!(size_of::<S1>(), 6);
+    assert_eq!(size_of::<S2>(), 6);
+}
+
diff --git a/src/test/run-pass/optimization-fuel-1.rs b/src/test/run-pass/optimization-fuel-1.rs
new file mode 100644
index 0000000000000..5f294e26aa53e
--- /dev/null
+++ b/src/test/run-pass/optimization-fuel-1.rs
@@ -0,0 +1,26 @@
+// Copyright 2012 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#![crate_name="foo"]
+
+use std::mem::size_of;
+
+// compile-flags: -Z fuel=foo=1
+
+struct S1(u8, u16, u8);
+struct S2(u8, u16, u8);
+
+fn main() {
+    let optimized = (size_of::<S1>() == 4) as usize
+        +(size_of::<S2>() == 4) as usize;
+    assert_eq!(optimized, 1);
+}
+
+
diff --git a/src/test/run-pass/type-sizes.rs b/src/test/run-pass/type-sizes.rs
index bbb01eaaf46b9..2f50e63153ea4 100644
--- a/src/test/run-pass/type-sizes.rs
+++ b/src/test/run-pass/type-sizes.rs
@@ -31,6 +31,17 @@ enum e3 {
     a([u16; 0], u8), b
 }
 
+struct ReorderedStruct {
+    a: u8,
+    b: u16,
+    c: u8
+}
+
+enum ReorderedEnum {
+    A(u8, u16, u8),
+    B(u8, u16, u8),
+}
+
 pub fn main() {
     assert_eq!(size_of::<u8>(), 1 as usize);
     assert_eq!(size_of::<u32>(), 4 as usize);
@@ -54,4 +65,6 @@ pub fn main() {
     assert_eq!(size_of::<e1>(), 8 as usize);
     assert_eq!(size_of::<e2>(), 8 as usize);
     assert_eq!(size_of::<e3>(), 4 as usize);
+    assert_eq!(size_of::<ReorderedStruct>(), 4);
+    assert_eq!(size_of::<ReorderedEnum>(), 6);
 }
diff --git a/src/test/ui/print-fuel/print-fuel.rs b/src/test/ui/print-fuel/print-fuel.rs
new file mode 100644
index 0000000000000..0d9e243763f78
--- /dev/null
+++ b/src/test/ui/print-fuel/print-fuel.rs
@@ -0,0 +1,21 @@
+// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#![crate_name="foo"]
+#![allow(dead_code)]
+
+// compile-flags: -Z print-fuel=foo
+
+struct S1(u8, u16, u8);
+struct S2(u8, u16, u8);
+struct S3(u8, u16, u8);
+
+fn main() {
+}
diff --git a/src/test/ui/print-fuel/print-fuel.stdout b/src/test/ui/print-fuel/print-fuel.stdout
new file mode 100644
index 0000000000000..cc88cc077bb21
--- /dev/null
+++ b/src/test/ui/print-fuel/print-fuel.stdout
@@ -0,0 +1 @@
+Fuel used by foo: 3
diff --git a/src/test/ui/print_type_sizes/nullable.stdout b/src/test/ui/print_type_sizes/nullable.stdout
index dd999c4a5e4c7..830678f174f88 100644
--- a/src/test/ui/print_type_sizes/nullable.stdout
+++ b/src/test/ui/print_type_sizes/nullable.stdout
@@ -1,25 +1,22 @@
-print-type-size type: `IndirectNonZero<u32>`: 20 bytes, alignment: 4 bytes
-print-type-size     field `.pre`: 1 bytes
-print-type-size     padding: 3 bytes
-print-type-size     field `.nested`: 12 bytes, alignment: 4 bytes
+print-type-size type: `IndirectNonZero<u32>`: 12 bytes, alignment: 4 bytes
+print-type-size     field `.nested`: 8 bytes
 print-type-size     field `.post`: 2 bytes
-print-type-size     end padding: 2 bytes
-print-type-size type: `MyOption<IndirectNonZero<u32>>`: 20 bytes, alignment: 4 bytes
-print-type-size     variant `Some`: 20 bytes
-print-type-size         field `.0`: 20 bytes
-print-type-size type: `EmbeddedDiscr`: 12 bytes, alignment: 4 bytes
-print-type-size     variant `Record`: 10 bytes
-print-type-size         field `.pre`: 1 bytes
-print-type-size         padding: 3 bytes
-print-type-size         field `.val`: 4 bytes, alignment: 4 bytes
-print-type-size         field `.post`: 2 bytes
-print-type-size     end padding: 2 bytes
-print-type-size type: `NestedNonZero<u32>`: 12 bytes, alignment: 4 bytes
 print-type-size     field `.pre`: 1 bytes
-print-type-size     padding: 3 bytes
-print-type-size     field `.val`: 4 bytes, alignment: 4 bytes
+print-type-size     end padding: 1 bytes
+print-type-size type: `MyOption<IndirectNonZero<u32>>`: 12 bytes, alignment: 4 bytes
+print-type-size     variant `Some`: 12 bytes
+print-type-size         field `.0`: 12 bytes
+print-type-size type: `EmbeddedDiscr`: 8 bytes, alignment: 4 bytes
+print-type-size     variant `Record`: 7 bytes
+print-type-size         field `.val`: 4 bytes
+print-type-size         field `.post`: 2 bytes
+print-type-size         field `.pre`: 1 bytes
+print-type-size     end padding: 1 bytes
+print-type-size type: `NestedNonZero<u32>`: 8 bytes, alignment: 4 bytes
+print-type-size     field `.val`: 4 bytes
 print-type-size     field `.post`: 2 bytes
-print-type-size     end padding: 2 bytes
+print-type-size     field `.pre`: 1 bytes
+print-type-size     end padding: 1 bytes
 print-type-size type: `MyOption<core::nonzero::NonZero<u32>>`: 4 bytes, alignment: 4 bytes
 print-type-size     variant `Some`: 4 bytes
 print-type-size         field `.0`: 4 bytes
diff --git a/src/test/ui/print_type_sizes/packed.stdout b/src/test/ui/print_type_sizes/packed.stdout
index 1278a7d7c92c6..83fd333c9c7fc 100644
--- a/src/test/ui/print_type_sizes/packed.stdout
+++ b/src/test/ui/print_type_sizes/packed.stdout
@@ -1,13 +1,11 @@
-print-type-size type: `Padded`: 16 bytes, alignment: 4 bytes
+print-type-size type: `Padded`: 12 bytes, alignment: 4 bytes
+print-type-size     field `.g`: 4 bytes
+print-type-size     field `.h`: 2 bytes
 print-type-size     field `.a`: 1 bytes
 print-type-size     field `.b`: 1 bytes
-print-type-size     padding: 2 bytes
-print-type-size     field `.g`: 4 bytes, alignment: 4 bytes
 print-type-size     field `.c`: 1 bytes
-print-type-size     padding: 1 bytes
-print-type-size     field `.h`: 2 bytes, alignment: 2 bytes
 print-type-size     field `.d`: 1 bytes
-print-type-size     end padding: 3 bytes
+print-type-size     end padding: 2 bytes
 print-type-size type: `Packed`: 10 bytes, alignment: 1 bytes
 print-type-size     field `.a`: 1 bytes
 print-type-size     field `.b`: 1 bytes
diff --git a/src/test/ui/print_type_sizes/padding.stdout b/src/test/ui/print_type_sizes/padding.stdout
index bb95f790bd9e4..0eaff7118b35c 100644
--- a/src/test/ui/print_type_sizes/padding.stdout
+++ b/src/test/ui/print_type_sizes/padding.stdout
@@ -1,10 +1,12 @@
 print-type-size type: `E1`: 12 bytes, alignment: 4 bytes
-print-type-size     discriminant: 4 bytes
-print-type-size     variant `A`: 5 bytes
-print-type-size         field `.0`: 4 bytes
+print-type-size     discriminant: 1 bytes
+print-type-size     variant `A`: 7 bytes
 print-type-size         field `.1`: 1 bytes
-print-type-size     variant `B`: 8 bytes
-print-type-size         field `.0`: 8 bytes
+print-type-size         padding: 2 bytes
+print-type-size         field `.0`: 4 bytes, alignment: 4 bytes
+print-type-size     variant `B`: 11 bytes
+print-type-size         padding: 3 bytes
+print-type-size         field `.0`: 8 bytes, alignment: 4 bytes
 print-type-size type: `E2`: 12 bytes, alignment: 4 bytes
 print-type-size     discriminant: 1 bytes
 print-type-size     variant `A`: 7 bytes
@@ -15,7 +17,7 @@ print-type-size     variant `B`: 11 bytes
 print-type-size         padding: 3 bytes
 print-type-size         field `.0`: 8 bytes, alignment: 4 bytes
 print-type-size type: `S`: 8 bytes, alignment: 4 bytes
+print-type-size     field `.g`: 4 bytes
 print-type-size     field `.a`: 1 bytes
 print-type-size     field `.b`: 1 bytes
-print-type-size     padding: 2 bytes
-print-type-size     field `.g`: 4 bytes, alignment: 4 bytes
+print-type-size     end padding: 2 bytes