rustc_target/callconv/x86.rs
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use crate::abi::call::{ArgAttribute, FnAbi, PassMode, Reg, RegKind};
use crate::abi::{Abi, Align, HasDataLayout, TyAbiInterface, TyAndLayout};
use crate::spec::HasTargetSpec;
#[derive(PartialEq)]
pub(crate) enum Flavor {
General,
FastcallOrVectorcall,
}
pub(crate) struct X86Options {
pub flavor: Flavor,
pub regparm: Option<u32>,
}
pub(crate) fn compute_abi_info<'a, Ty, C>(cx: &C, fn_abi: &mut FnAbi<'a, Ty>, opts: X86Options)
where
Ty: TyAbiInterface<'a, C> + Copy,
C: HasDataLayout + HasTargetSpec,
{
if !fn_abi.ret.is_ignore() {
if fn_abi.ret.layout.is_aggregate() && fn_abi.ret.layout.is_sized() {
// Returning a structure. Most often, this will use
// a hidden first argument. On some platforms, though,
// small structs are returned as integers.
//
// Some links:
// https://www.angelcode.com/dev/callconv/callconv.html
// Clang's ABI handling is in lib/CodeGen/TargetInfo.cpp
let t = cx.target_spec();
if t.abi_return_struct_as_int {
// According to Clang, everyone but MSVC returns single-element
// float aggregates directly in a floating-point register.
if !t.is_like_msvc && fn_abi.ret.layout.is_single_fp_element(cx) {
match fn_abi.ret.layout.size.bytes() {
4 => fn_abi.ret.cast_to(Reg::f32()),
8 => fn_abi.ret.cast_to(Reg::f64()),
_ => fn_abi.ret.make_indirect(),
}
} else {
match fn_abi.ret.layout.size.bytes() {
1 => fn_abi.ret.cast_to(Reg::i8()),
2 => fn_abi.ret.cast_to(Reg::i16()),
4 => fn_abi.ret.cast_to(Reg::i32()),
8 => fn_abi.ret.cast_to(Reg::i64()),
_ => fn_abi.ret.make_indirect(),
}
}
} else {
fn_abi.ret.make_indirect();
}
} else {
fn_abi.ret.extend_integer_width_to(32);
}
}
for arg in fn_abi.args.iter_mut() {
if arg.is_ignore() || !arg.layout.is_sized() {
continue;
}
// FIXME: MSVC 2015+ will pass the first 3 vector arguments in [XYZ]MM0-2
// See https://reviews.llvm.org/D72114 for Clang behavior
let t = cx.target_spec();
let align_4 = Align::from_bytes(4).unwrap();
let align_16 = Align::from_bytes(16).unwrap();
if t.is_like_msvc
&& arg.layout.is_adt()
&& let Some(max_repr_align) = arg.layout.max_repr_align
&& max_repr_align > align_4
{
// MSVC has special rules for overaligned arguments: https://reviews.llvm.org/D72114.
// Summarized here:
// - Arguments with _requested_ alignment > 4 are passed indirectly.
// - For backwards compatibility, arguments with natural alignment > 4 are still passed
// on stack (via `byval`). For example, this includes `double`, `int64_t`,
// and structs containing them, provided they lack an explicit alignment attribute.
assert!(
arg.layout.align.abi >= max_repr_align,
"abi alignment {:?} less than requested alignment {max_repr_align:?}",
arg.layout.align.abi,
);
arg.make_indirect();
} else if arg.layout.is_aggregate() {
// We need to compute the alignment of the `byval` argument. The rules can be found in
// `X86_32ABIInfo::getTypeStackAlignInBytes` in Clang's `TargetInfo.cpp`. Summarized
// here, they are:
//
// 1. If the natural alignment of the type is <= 4, the alignment is 4.
//
// 2. Otherwise, on Linux, the alignment of any vector type is the natural alignment.
// This doesn't matter here because we only pass aggregates via `byval`, not vectors.
//
// 3. Otherwise, on Apple platforms, the alignment of anything that contains a vector
// type is 16.
//
// 4. If none of these conditions are true, the alignment is 4.
fn contains_vector<'a, Ty, C>(cx: &C, layout: TyAndLayout<'a, Ty>) -> bool
where
Ty: TyAbiInterface<'a, C> + Copy,
{
match layout.abi {
Abi::Uninhabited | Abi::Scalar(_) | Abi::ScalarPair(..) => false,
Abi::Vector { .. } => true,
Abi::Aggregate { .. } => {
for i in 0..layout.fields.count() {
if contains_vector(cx, layout.field(cx, i)) {
return true;
}
}
false
}
}
}
let byval_align = if arg.layout.align.abi < align_4 {
// (1.)
align_4
} else if t.is_like_osx && contains_vector(cx, arg.layout) {
// (3.)
align_16
} else {
// (4.)
align_4
};
arg.pass_by_stack_offset(Some(byval_align));
} else {
arg.extend_integer_width_to(32);
}
}
fill_inregs(cx, fn_abi, opts, false);
}
pub(crate) fn fill_inregs<'a, Ty, C>(
cx: &C,
fn_abi: &mut FnAbi<'a, Ty>,
opts: X86Options,
rust_abi: bool,
) where
Ty: TyAbiInterface<'a, C> + Copy,
{
if opts.flavor != Flavor::FastcallOrVectorcall && opts.regparm.is_none_or(|x| x == 0) {
return;
}
// Mark arguments as InReg like clang does it,
// so our fastcall/vectorcall is compatible with C/C++ fastcall/vectorcall.
// Clang reference: lib/CodeGen/TargetInfo.cpp
// See X86_32ABIInfo::shouldPrimitiveUseInReg(), X86_32ABIInfo::updateFreeRegs()
// IsSoftFloatABI is only set to true on ARM platforms,
// which in turn can't be x86?
// 2 for fastcall/vectorcall, regparm limited by 3 otherwise
let mut free_regs = opts.regparm.unwrap_or(2).into();
// For types generating PassMode::Cast, InRegs will not be set.
// Maybe, this is a FIXME
let has_casts = fn_abi.args.iter().any(|arg| matches!(arg.mode, PassMode::Cast { .. }));
if has_casts && rust_abi {
return;
}
for arg in fn_abi.args.iter_mut() {
let attrs = match arg.mode {
PassMode::Ignore | PassMode::Indirect { attrs: _, meta_attrs: None, on_stack: _ } => {
continue;
}
PassMode::Direct(ref mut attrs) => attrs,
PassMode::Pair(..)
| PassMode::Indirect { attrs: _, meta_attrs: Some(_), on_stack: _ }
| PassMode::Cast { .. } => {
unreachable!("x86 shouldn't be passing arguments by {:?}", arg.mode)
}
};
// At this point we know this must be a primitive of sorts.
let unit = arg.layout.homogeneous_aggregate(cx).unwrap().unit().unwrap();
assert_eq!(unit.size, arg.layout.size);
if matches!(unit.kind, RegKind::Float | RegKind::Vector) {
continue;
}
let size_in_regs = (arg.layout.size.bits() + 31) / 32;
if size_in_regs == 0 {
continue;
}
if size_in_regs > free_regs {
break;
}
free_regs -= size_in_regs;
if arg.layout.size.bits() <= 32 && unit.kind == RegKind::Integer {
attrs.set(ArgAttribute::InReg);
}
if free_regs == 0 {
break;
}
}
}