librustc: implement a #[packed] attribute for structs.

A struct (inc. tuple struct) can be annotated with #[packed], so that there
is no padding between its elements, like GCC's `__attribute__((packed))`.

Closes rust-lang#1704

src/librustc/middle/trans/adt.rs

@@ -88,6 +88,7 @@ pub enum Repr {
 struct Struct {
     size: u64,
     align: u64,
+    packed: bool,
     fields: ~[ty::t]
 }
 
@@ -109,17 +110,18 @@ pub fn represent_type(cx: @CrateContext, t: ty::t) -> @Repr {
     }
     let repr = @match ty::get(t).sty {
         ty::ty_tup(ref elems) => {
-            Univariant(mk_struct(cx, *elems), false)
+            Univariant(mk_struct(cx, *elems, false), false)
         }
         ty::ty_struct(def_id, ref substs) => {
             let fields = ty::lookup_struct_fields(cx.tcx, def_id);
             let ftys = do fields.map |field| {
                 ty::lookup_field_type(cx.tcx, def_id, field.id, substs)
             };
+            let packed = ty::lookup_packed(cx.tcx, def_id);
             let dtor = ty::ty_dtor(cx.tcx, def_id).is_present();
             let ftys =
                 if dtor { ftys + [ty::mk_bool(cx.tcx)] } else { ftys };
-            Univariant(mk_struct(cx, ftys), dtor)
+            Univariant(mk_struct(cx, ftys, packed), dtor)
         }
         ty::ty_enum(def_id, ref substs) => {
             struct Case { discr: int, tys: ~[ty::t] };
@@ -132,15 +134,15 @@ pub fn represent_type(cx: @CrateContext, t: ty::t) -> @Repr {
             };
             if cases.len() == 0 {
                 // Uninhabitable; represent as unit
-                Univariant(mk_struct(cx, ~[]), false)
+                Univariant(mk_struct(cx, ~[], false), false)
             } else if cases.all(|c| c.tys.len() == 0) {
                 // All bodies empty -> intlike
                 let discrs = cases.map(|c| c.discr);
                 CEnum(discrs.min(), discrs.max())
             } else if cases.len() == 1 {
                 // Equivalent to a struct/tuple/newtype.
                 assert!(cases[0].discr == 0);
-                Univariant(mk_struct(cx, cases[0].tys), false)
+                Univariant(mk_struct(cx, cases[0].tys, false), false)
             } else {
                 // The general case.  Since there's at least one
                 // non-empty body, explicit discriminants should have
@@ -151,7 +153,7 @@ pub fn represent_type(cx: @CrateContext, t: ty::t) -> @Repr {
                                      ty::item_path_str(cx.tcx, def_id)))
                 }
                 let discr = ~[ty::mk_int(cx.tcx)];
-                General(cases.map(|c| mk_struct(cx, discr + c.tys)))
+                General(cases.map(|c| mk_struct(cx, discr + c.tys, false)))
             }
         }
         _ => cx.sess.bug(~"adt::represent_type called on non-ADT type")
@@ -160,12 +162,13 @@ pub fn represent_type(cx: @CrateContext, t: ty::t) -> @Repr {
     return repr;
 }
 
-fn mk_struct(cx: @CrateContext, tys: &[ty::t]) -> Struct {
+fn mk_struct(cx: @CrateContext, tys: &[ty::t], packed: bool) -> Struct {
     let lltys = tys.map(|&ty| type_of::sizing_type_of(cx, ty));
-    let llty_rec = T_struct(lltys);
+    let llty_rec = T_struct(lltys, packed);
     Struct {
         size: machine::llsize_of_alloc(cx, llty_rec) /*bad*/as u64,
         align: machine::llalign_of_min(cx, llty_rec) /*bad*/as u64,
+        packed: packed,
         fields: vec::from_slice(tys)
     }
 }
@@ -358,7 +361,8 @@ fn struct_field_ptr(bcx: block, st: &Struct, val: ValueRef, ix: uint,
 
     let val = if needs_cast {
         let real_llty = T_struct(st.fields.map(
-            |&ty| type_of::type_of(ccx, ty)));
+            |&ty| type_of::type_of(ccx, ty)),
+                                 st.packed);
         PointerCast(bcx, val, T_ptr(real_llty))
     } else {
         val

src/librustc/middle/trans/asm.rs

@@ -1,4 +1,4 @@
-// Copyright 2012 The Rust Project Developers. See the COPYRIGHT
+// Copyright 2012-2013 The Rust Project Developers. See the COPYRIGHT
 // file at the top-level directory of this distribution and at
 // http://rust-lang.org/COPYRIGHT.
 //
@@ -108,7 +108,7 @@ pub fn trans_inline_asm(bcx: block, ia: &ast::inline_asm) -> block {
     } else if numOutputs == 1 {
         val_ty(outputs[0])
     } else {
-        T_struct(outputs.map(|o| val_ty(*o)))
+        T_struct(outputs.map(|o| val_ty(*o)), false)
     };
 
     let dialect = match ia.dialect {

src/librustc/middle/trans/base.rs

@@ -1,4 +1,4 @@
-// Copyright 2012 The Rust Project Developers. See the COPYRIGHT
+// Copyright 2012-2013 The Rust Project Developers. See the COPYRIGHT
 // file at the top-level directory of this distribution and at
 // http://rust-lang.org/COPYRIGHT.
 //
@@ -938,7 +938,7 @@ pub fn get_landing_pad(bcx: block) -> BasicBlockRef {
     // The landing pad return type (the type being propagated). Not sure what
     // this represents but it's determined by the personality function and
     // this is what the EH proposal example uses.
-    let llretty = T_struct(~[T_ptr(T_i8()), T_i32()]);
+    let llretty = T_struct(~[T_ptr(T_i8()), T_i32()], false);
     // The exception handling personality function. This is the C++
     // personality function __gxx_personality_v0, wrapped in our naming
     // convention.
@@ -2837,7 +2837,7 @@ pub fn decl_gc_metadata(ccx: @CrateContext, llmod_id: &str) {
 }
 
 pub fn create_module_map(ccx: @CrateContext) -> ValueRef {
-    let elttype = T_struct(~[ccx.int_type, ccx.int_type]);
+    let elttype = T_struct(~[ccx.int_type, ccx.int_type], false);
     let maptype = T_array(elttype, ccx.module_data.len() + 1);
     let map = str::as_c_str(~"_rust_mod_map", |buf| {
         unsafe {
@@ -2877,7 +2877,7 @@ pub fn decl_crate_map(sess: session::Session, mapmeta: LinkMeta,
     };
     let sym_name = ~"_rust_crate_map_" + mapname;
     let arrtype = T_array(int_type, n_subcrates as uint);
-    let maptype = T_struct(~[T_i32(), T_ptr(T_i8()), int_type, arrtype]);
+    let maptype = T_struct(~[T_i32(), T_ptr(T_i8()), int_type, arrtype], false);
     let map = str::as_c_str(sym_name, |buf| {
         unsafe {
             llvm::LLVMAddGlobal(llmod, maptype, buf)

src/librustc/middle/trans/cabi_arm.rs

@@ -12,6 +12,7 @@ use lib::llvm::{llvm, Integer, Pointer, Float, Double, Struct, Array};
 use lib::llvm::struct_tys;
 use lib::llvm::TypeRef;
 use lib::llvm::{Attribute, StructRetAttribute};
+use lib::llvm::True;
 use middle::trans::cabi::{ABIInfo, FnType, LLVMType};
 use middle::trans::common::{T_i8, T_i16, T_i32, T_i64};
 use middle::trans::common::{T_array, T_ptr, T_void};
@@ -39,8 +40,12 @@ fn ty_align(ty: TypeRef) -> uint {
             Float => 4,
             Double => 8,
             Struct => {
-                do vec::foldl(1, struct_tys(ty)) |a, t| {
-                    uint::max(a, ty_align(*t))
+                if llvm::LLVMIsPackedStruct(ty) == True {
+                    1
+                } else {
+                    do vec::foldl(1, struct_tys(ty)) |a, t| {
+                        uint::max(a, ty_align(*t))
+                    }
                 }
             }
             Array => {
@@ -62,10 +67,16 @@ fn ty_size(ty: TypeRef) -> uint {
             Float => 4,
             Double => 8,
             Struct => {
-                let size = do vec::foldl(0, struct_tys(ty)) |s, t| {
-                    align(s, *t) + ty_size(*t)
-                };
-                align(size, ty)
+                if llvm::LLVMIsPackedStruct(ty) == True {
+                    do vec::foldl(0, struct_tys(ty)) |s, t| {
+                        s + ty_size(*t)
+                    }
+                } else {
+                    let size = do vec::foldl(0, struct_tys(ty)) |s, t| {
+                        align(s, *t) + ty_size(*t)
+                    };
+                    align(size, ty)
+                }
             }
             Array => {
                 let len = llvm::LLVMGetArrayLength(ty) as uint;

src/librustc/middle/trans/cabi_mips.rs

@@ -1,4 +1,4 @@
-// Copyright 2012 The Rust Project Developers. See the COPYRIGHT
+// Copyright 2012-2013 The Rust Project Developers. See the COPYRIGHT
 // file at the top-level directory of this distribution and at
 // http://rust-lang.org/COPYRIGHT.
 //
@@ -14,6 +14,7 @@ use core::libc::c_uint;
 use lib::llvm::{llvm, TypeRef, Integer, Pointer, Float, Double};
 use lib::llvm::{Struct, Array, Attribute};
 use lib::llvm::{StructRetAttribute};
+use lib::llvm::True;
 use middle::trans::common::*;
 use middle::trans::cabi::*;
 
@@ -49,8 +50,12 @@ fn ty_align(ty: TypeRef) -> uint {
             Float => 4,
             Double => 8,
             Struct => {
-              do vec::foldl(1, struct_tys(ty)) |a, t| {
-                  uint::max(a, ty_align(*t))
+              if llvm::LLVMIsPackedStruct(ty) == True {
+                1
+              } else {
+                do vec::foldl(1, struct_tys(ty)) |a, t| {
+                    uint::max(a, ty_align(*t))
+                }
               }
             }
             Array => {
@@ -72,10 +77,16 @@ fn ty_size(ty: TypeRef) -> uint {
             Float => 4,
             Double => 8,
             Struct => {
-              let size = do vec::foldl(0, struct_tys(ty)) |s, t| {
-                  align(s, *t) + ty_size(*t)
-              };
-              align(size, ty)
+                if llvm::LLVMIsPackedStruct(ty) == True {
+                    do vec::foldl(0, struct_tys(ty)) |s, t| {
+                        s + ty_size(*t)
+                    }
+                } else {
+                    let size = do vec::foldl(0, struct_tys(ty)) |s, t| {
+                        align(s, *t) + ty_size(*t)
+                    };
+                    align(size, ty)
+                }
             }
             Array => {
               let len = llvm::LLVMGetArrayLength(ty) as uint;
@@ -174,7 +185,7 @@ fn struct_ty(ty: TypeRef,
         fields.push(ty);
     }
 
-    return T_struct(fields);
+    return T_struct(fields, false);
 }
 
 enum MIPS_ABIInfo { MIPS_ABIInfo }

src/librustc/middle/trans/cabi_x86_64.rs

@@ -1,4 +1,4 @@
-// Copyright 2012 The Rust Project Developers. See the COPYRIGHT
+// Copyright 2012-2013 The Rust Project Developers. See the COPYRIGHT
 // file at the top-level directory of this distribution and at
 // http://rust-lang.org/COPYRIGHT.
 //
@@ -15,6 +15,7 @@ use lib::llvm::{llvm, TypeRef, Integer, Pointer, Float, Double};
 use lib::llvm::{Struct, Array, Attribute};
 use lib::llvm::{StructRetAttribute, ByValAttribute};
 use lib::llvm::struct_tys;
+use lib::llvm::True;
 use middle::trans::common::*;
 use middle::trans::cabi::*;
 
@@ -76,8 +77,12 @@ fn classify_ty(ty: TypeRef) -> ~[x86_64_reg_class] {
                 Float => 4,
                 Double => 8,
                 Struct => {
-                  do vec::foldl(1, struct_tys(ty)) |a, t| {
+                  if llvm::LLVMIsPackedStruct(ty) == True {
+                    1
+                  } else {
+                    do vec::foldl(1, struct_tys(ty)) |a, t| {
                       uint::max(a, ty_align(*t))
+                    }
                   }
                 }
                 Array => {
@@ -99,10 +104,16 @@ fn classify_ty(ty: TypeRef) -> ~[x86_64_reg_class] {
                 Float => 4,
                 Double => 8,
                 Struct => {
-                  let size = do vec::foldl(0, struct_tys(ty)) |s, t| {
+                  if llvm::LLVMIsPackedStruct(ty) == True {
+                    do vec::foldl(0, struct_tys(ty)) |s, t| {
+                      s + ty_size(*t)
+                    }
+                  } else {
+                    let size = do vec::foldl(0, struct_tys(ty)) |s, t| {
                       align(s, *t) + ty_size(*t)
-                  };
-                  align(size, ty)
+                    };
+                    align(size, ty)
+                  }
                 }
                 Array => {
                   let len = llvm::LLVMGetArrayLength(ty) as uint;
@@ -308,7 +319,7 @@ fn llreg_ty(cls: &[x86_64_reg_class]) -> TypeRef {
             }
             i += 1u;
         }
-        return T_struct(tys);
+        return T_struct(tys, false);
     }
 }