src/librustc_trans/trans/machine.rs

   1 // Copyright 2012-2013 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 // Information concerning the machine representation of various types.
  12
  13 #![allow(non_camel_case_types)]
  14
  15 use llvm::{self, ValueRef};
  16 use trans::common::*;
  17
  18 use trans::type_::Type;
  19
  20 pub type llbits = u64;
  21 pub type llsize = u64;
  22 pub type llalign = u32;
  23
  24 // ______________________________________________________________________
  25 // compute sizeof / alignof
  26
  27 // Returns the number of bytes clobbered by a Store to this type.
  28 pub fn llsize_of_store(cx: &CrateContext, ty: Type) -> llsize {
  29     unsafe {
  30         return llvm::LLVMStoreSizeOfType(cx.td().lltd, ty.to_ref());
  31     }
  32 }
  33
  34 // Returns the number of bytes between successive elements of type T in an
  35 // array of T. This is the "ABI" size. It includes any ABI-mandated padding.
  36 pub fn llsize_of_alloc(cx: &CrateContext, ty: Type) -> llsize {
  37     unsafe {
  38         return llvm::LLVMABISizeOfType(cx.td().lltd, ty.to_ref());
  39     }
  40 }
  41
  42 // Returns, as near as we can figure, the "real" size of a type. As in, the
  43 // bits in this number of bytes actually carry data related to the datum
  44 // with the type. Not junk, accidentally-damaged words, or whatever.
  45 // Note that padding of the type will be included for structs, but not for the
  46 // other types (i.e. SIMD types).
  47 // Rounds up to the nearest byte though, so if you have a 1-bit
  48 // value, we return 1 here, not 0. Most of rustc works in bytes. Be warned
  49 // that LLVM *does* distinguish between e.g. a 1-bit value and an 8-bit value
  50 // at the codegen level! In general you should prefer `llbitsize_of_real`
  51 // below.
  52 pub fn llsize_of_real(cx: &CrateContext, ty: Type) -> llsize {
  53     unsafe {
  54         let nbits = llvm::LLVMSizeOfTypeInBits(cx.td().lltd, ty.to_ref());
  55         if nbits & 7 != 0 {
  56             // Not an even number of bytes, spills into "next" byte.
  57             1 + (nbits >> 3)
  58         } else {
  59             nbits >> 3
  60         }
  61     }
  62 }
  63
  64 /// Returns the "real" size of the type in bits.
  65 pub fn llbitsize_of_real(cx: &CrateContext, ty: Type) -> llbits {
  66     unsafe {
  67         llvm::LLVMSizeOfTypeInBits(cx.td().lltd, ty.to_ref())
  68     }
  69 }
  70
  71 /// Returns the size of the type as an LLVM constant integer value.
  72 pub fn llsize_of(cx: &CrateContext, ty: Type) -> ValueRef {
  73     // Once upon a time, this called LLVMSizeOf, which does a
  74     // getelementptr(1) on a null pointer and casts to an int, in
  75     // order to obtain the type size as a value without requiring the
  76     // target data layout.  But we have the target data layout, so
  77     // there's no need for that contrivance.  The instruction
  78     // selection DAG generator would flatten that GEP(1) node into a
  79     // constant of the type's alloc size, so let's save it some work.
  80     return C_uint(cx, llsize_of_alloc(cx, ty));
  81 }
  82
  83 // Returns the preferred alignment of the given type for the current target.
  84 // The preferred alignment may be larger than the alignment used when
  85 // packing the type into structs. This will be used for things like
  86 // allocations inside a stack frame, which LLVM has a free hand in.
  87 pub fn llalign_of_pref(cx: &CrateContext, ty: Type) -> llalign {
  88     unsafe {
  89         return llvm::LLVMPreferredAlignmentOfType(cx.td().lltd, ty.to_ref());
  90     }
  91 }
  92
  93 // Returns the minimum alignment of a type required by the platform.
  94 // This is the alignment that will be used for struct fields, arrays,
  95 // and similar ABI-mandated things.
  96 pub fn llalign_of_min(cx: &CrateContext, ty: Type) -> llalign {
  97     unsafe {
  98         return llvm::LLVMABIAlignmentOfType(cx.td().lltd, ty.to_ref());
  99     }
 100 }
 101
 102 pub fn llelement_offset(cx: &CrateContext, struct_ty: Type, element: usize) -> u64 {
 103     unsafe {
 104         return llvm::LLVMOffsetOfElement(cx.td().lltd,
 105                                          struct_ty.to_ref(),
 106                                          element as u32);
 107     }
 108 }