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Store scalar pair bools as i8 in memory

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We represent `bool` as `i1` in a `ScalarPair`, unlike other aggregates,
to optimize IR for checked operators and the like.  With this patch, we
still do so when the pair is an immediate value, but we use the `i8`
memory type when the value is loaded or stored as an LLVM aggregate.

So `(bool, bool)` looks like an `{ i1, i1 }` immediate, but `{ i8, i8 }`
in memory.  When a pair is a direct function argument, `PassMode::Pair`,
it is still passed using the immediate `i1` type, but as a return value
it will use the `i8` memory type.  Also, `bool`-like` enum tags will now
use scalar pairs when possible, where they were previously excluded due
to optimization issues.
This commit is contained in:
Josh Stone 2018-06-15 15:47:54 -07:00
parent 94eb176055
commit e578976560
9 changed files with 84 additions and 44 deletions
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9
src/librustc/ty/layout.rs
View File

@ -1020,13 +1020,8 @@ impl<'a, 'tcx> LayoutCx<'tcx, TyCtxt<'a, 'tcx, 'tcx>> {
let mut abi = Abi::Aggregate { sized: true };
if tag.value.size(dl) == size {
abi = Abi::Scalar(tag.clone());
} else if !tag.is_bool() {
// HACK(nox): Blindly using ScalarPair for all tagged enums
// where applicable leads to Option<u8> being handled as {i1, i8},
// which later confuses SROA and some loop optimisations,
// ultimately leading to the repeat-trusted-len test
// failing. We make the trade-off of using ScalarPair only
// for types where the tag isn't a boolean.
} else {
// Try to use a ScalarPair for all tagged enums.
let mut common_prim = None;
for (field_layouts, layout_variant) in variants.iter().zip(&layout_variants) {
let offsets = match layout_variant.fields {

4
src/librustc_codegen_llvm/abi.rs
View File

@ -582,8 +582,8 @@ impl<'a, 'tcx> FnTypeExt<'a, 'tcx> for FnType<'tcx, Ty<'tcx>> {
PassMode::Ignore => continue,
PassMode::Direct(_) => arg.layout.immediate_llvm_type(cx),
PassMode::Pair(..) => {
llargument_tys.push(arg.layout.scalar_pair_element_llvm_type(cx, 0));
llargument_tys.push(arg.layout.scalar_pair_element_llvm_type(cx, 1));
llargument_tys.push(arg.layout.scalar_pair_element_llvm_type(cx, 0, true));
llargument_tys.push(arg.layout.scalar_pair_element_llvm_type(cx, 1, true));
continue;
}
PassMode::Cast(cast) => cast.llvm_type(cx),

15
src/librustc_codegen_llvm/base.rs
View File

@ -265,8 +265,8 @@ pub fn unsize_thin_ptr<'a, 'tcx>(
}
let (lldata, llextra) = result.unwrap();
// HACK(eddyb) have to bitcast pointers until LLVM removes pointee types.
(bx.bitcast(lldata, dst_layout.scalar_pair_element_llvm_type(bx.cx, 0)),
bx.bitcast(llextra, dst_layout.scalar_pair_element_llvm_type(bx.cx, 1)))
(bx.bitcast(lldata, dst_layout.scalar_pair_element_llvm_type(bx.cx, 0, true)),
bx.bitcast(llextra, dst_layout.scalar_pair_element_llvm_type(bx.cx, 1, true)))
}
_ => bug!("unsize_thin_ptr: called on bad types"),
}
@ -396,9 +396,14 @@ pub fn from_immediate(bx: &Builder, val: ValueRef) -> ValueRef {
pub fn to_immediate(bx: &Builder, val: ValueRef, layout: layout::TyLayout) -> ValueRef {
if let layout::Abi::Scalar(ref scalar) = layout.abi {
if scalar.is_bool() {
return bx.trunc(val, Type::i1(bx.cx));
}
return to_immediate_scalar(bx, val, scalar);
}
val
}
pub fn to_immediate_scalar(bx: &Builder, val: ValueRef, scalar: &layout::Scalar) -> ValueRef {
if scalar.is_bool() {
return bx.trunc(val, Type::i1(bx.cx));
}
val
}

23
src/librustc_codegen_llvm/mir/operand.rs
View File

@ -128,13 +128,13 @@ impl<'a, 'tcx> OperandRef<'tcx> {
bx.cx,
a,
a_scalar,
layout.scalar_pair_element_llvm_type(bx.cx, 0),
layout.scalar_pair_element_llvm_type(bx.cx, 0, true),
);
let b_llval = scalar_to_llvm(
bx.cx,
b,
b_scalar,
layout.scalar_pair_element_llvm_type(bx.cx, 1),
layout.scalar_pair_element_llvm_type(bx.cx, 1, true),
);
OperandValue::Pair(a_llval, b_llval)
},
@ -193,8 +193,8 @@ impl<'a, 'tcx> OperandRef<'tcx> {
self, llty);
// Reconstruct the immediate aggregate.
let mut llpair = C_undef(llty);
llpair = bx.insert_value(llpair, a, 0);
llpair = bx.insert_value(llpair, b, 1);
llpair = bx.insert_value(llpair, base::from_immediate(bx, a), 0);
llpair = bx.insert_value(llpair, base::from_immediate(bx, b), 1);
llpair
} else {
self.immediate()
@ -206,13 +206,14 @@ impl<'a, 'tcx> OperandRef<'tcx> {
llval: ValueRef,
layout: TyLayout<'tcx>)
-> OperandRef<'tcx> {
let val = if layout.is_llvm_scalar_pair() {
let val = if let layout::Abi::ScalarPair(ref a, ref b) = layout.abi {
debug!("Operand::from_immediate_or_packed_pair: unpacking {:?} @ {:?}",
llval, layout);
// Deconstruct the immediate aggregate.
OperandValue::Pair(bx.extract_value(llval, 0),
bx.extract_value(llval, 1))
let a_llval = base::to_immediate_scalar(bx, bx.extract_value(llval, 0), a);
let b_llval = base::to_immediate_scalar(bx, bx.extract_value(llval, 1), b);
OperandValue::Pair(a_llval, b_llval)
} else {
OperandValue::Immediate(llval)
};
@ -264,8 +265,8 @@ impl<'a, 'tcx> OperandRef<'tcx> {
*llval = bx.bitcast(*llval, field.immediate_llvm_type(bx.cx));
}
OperandValue::Pair(ref mut a, ref mut b) => {
*a = bx.bitcast(*a, field.scalar_pair_element_llvm_type(bx.cx, 0));
*b = bx.bitcast(*b, field.scalar_pair_element_llvm_type(bx.cx, 1));
*a = bx.bitcast(*a, field.scalar_pair_element_llvm_type(bx.cx, 0, true));
*b = bx.bitcast(*b, field.scalar_pair_element_llvm_type(bx.cx, 1, true));
}
OperandValue::Ref(..) => bug!()
}
@ -308,10 +309,10 @@ impl<'a, 'tcx> OperandValue {
}
OperandValue::Pair(a, b) => {
for (i, &x) in [a, b].iter().enumerate() {
let mut llptr = bx.struct_gep(dest.llval, i as u64);
let llptr = bx.struct_gep(dest.llval, i as u64);
// Make sure to always store i1 as i8.
if common::val_ty(x) == Type::i1(bx.cx) {
llptr = bx.pointercast(llptr, Type::i8p(bx.cx));
assert_eq!(common::val_ty(llptr), Type::i8p(bx.cx));
}
let val = base::from_immediate(bx, x);
bx.store_with_flags(val, llptr, dest.align, flags);

6
src/librustc_codegen_llvm/mir/place.rs
View File

@ -16,7 +16,7 @@ use rustc::mir::tcx::PlaceTy;
use rustc_data_structures::indexed_vec::Idx;
use base;
use builder::Builder;
use common::{CodegenCx, C_undef, C_usize, C_u8, C_u32, C_uint, C_null, C_uint_big};
use common::{CodegenCx, C_undef, C_usize, C_u8, C_u32, C_uint, C_null, C_uint_big, val_ty};
use consts;
use type_of::LayoutLlvmExt;
use type_::Type;
@ -127,10 +127,10 @@ impl<'a, 'tcx> PlaceRef<'tcx> {
OperandValue::Immediate(base::to_immediate(bx, llval, self.layout))
} else if let layout::Abi::ScalarPair(ref a, ref b) = self.layout.abi {
let load = |i, scalar: &layout::Scalar| {
let mut llptr = bx.struct_gep(self.llval, i as u64);
let llptr = bx.struct_gep(self.llval, i as u64);
// Make sure to always load i1 as i8.
if scalar.is_bool() {
llptr = bx.pointercast(llptr, Type::i8p(bx.cx));
assert_eq!(val_ty(llptr), Type::i8p(bx.cx));
}
let load = bx.load(llptr, self.align);
scalar_load_metadata(load, scalar);

4
src/librustc_codegen_llvm/mir/rvalue.rs
View File

@ -232,7 +232,7 @@ impl<'a, 'tcx> FunctionCx<'a, 'tcx> {
// HACK(eddyb) have to bitcast pointers
// until LLVM removes pointee types.
let lldata = bx.pointercast(lldata,
cast.scalar_pair_element_llvm_type(bx.cx, 0));
cast.scalar_pair_element_llvm_type(bx.cx, 0, true));
OperandValue::Pair(lldata, llextra)
}
OperandValue::Immediate(lldata) => {
@ -251,7 +251,7 @@ impl<'a, 'tcx> FunctionCx<'a, 'tcx> {
if let OperandValue::Pair(data_ptr, meta) = operand.val {
if cast.is_llvm_scalar_pair() {
let data_cast = bx.pointercast(data_ptr,
cast.scalar_pair_element_llvm_type(bx.cx, 0));
cast.scalar_pair_element_llvm_type(bx.cx, 0, true));
OperandValue::Pair(data_cast, meta)
} else { // cast to thin-ptr
// Cast of fat-ptr to thin-ptr is an extraction of data-ptr and

25
src/librustc_codegen_llvm/type_of.rs
View File

@ -47,8 +47,8 @@ fn uncached_llvm_type<'a, 'tcx>(cx: &CodegenCx<'a, 'tcx>,
}
layout::Abi::ScalarPair(..) => {
return Type::struct_(cx, &[
layout.scalar_pair_element_llvm_type(cx, 0),
layout.scalar_pair_element_llvm_type(cx, 1),
layout.scalar_pair_element_llvm_type(cx, 0, false),
layout.scalar_pair_element_llvm_type(cx, 1, false),
], false);
}
layout::Abi::Uninhabited |
@ -206,7 +206,7 @@ pub trait LayoutLlvmExt<'tcx> {
fn scalar_llvm_type_at<'a>(&self, cx: &CodegenCx<'a, 'tcx>,
scalar: &layout::Scalar, offset: Size) -> Type;
fn scalar_pair_element_llvm_type<'a>(&self, cx: &CodegenCx<'a, 'tcx>,
index: usize) -> Type;
index: usize, immediate: bool) -> Type;
fn llvm_field_index(&self, index: usize) -> u64;
fn pointee_info_at<'a>(&self, cx: &CodegenCx<'a, 'tcx>, offset: Size)
-> Option<PointeeInfo>;
@ -340,7 +340,7 @@ impl<'tcx> LayoutLlvmExt<'tcx> for TyLayout<'tcx> {
}
fn scalar_pair_element_llvm_type<'a>(&self, cx: &CodegenCx<'a, 'tcx>,
index: usize) -> Type {
index: usize, immediate: bool) -> Type {
// HACK(eddyb) special-case fat pointers until LLVM removes
// pointee types, to avoid bitcasting every `OperandRef::deref`.
match self.ty.sty {
@ -350,7 +350,7 @@ impl<'tcx> LayoutLlvmExt<'tcx> for TyLayout<'tcx> {
}
ty::TyAdt(def, _) if def.is_box() => {
let ptr_ty = cx.tcx.mk_mut_ptr(self.ty.boxed_ty());
return cx.layout_of(ptr_ty).scalar_pair_element_llvm_type(cx, index);
return cx.layout_of(ptr_ty).scalar_pair_element_llvm_type(cx, index, immediate);
}
_ => {}
}
@ -361,14 +361,13 @@ impl<'tcx> LayoutLlvmExt<'tcx> for TyLayout<'tcx> {
};
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() {
// Make sure to return the same type `immediate_llvm_type` would when
// dealing with an immediate pair. This means that `(bool, bool)` is
// effectively represented as `{i8, i8}` in memory and `{i1, i1}` as an
// immediate, just like `bool` is typically `i8` in memory and only `i1`
// when immediate. We need to load/store `bool` as `i8` to avoid
// crippling LLVM optimizations or triggering other LLVM bugs with `i1`.
if immediate && scalar.is_bool() {
return Type::i1(cx);
}

2
src/test/codegen/function-arguments.rs
View File

@ -149,7 +149,7 @@ pub fn enum_id_1(x: Option<Result<u16, u16>>) -> Option<Result<u16, u16>> {
x
}
// CHECK: i16 @enum_id_2(i16)
// CHECK: { i8, i8 } @enum_id_2(i1 zeroext %x.0, i8 %x.1)
#[no_mangle]
pub fn enum_id_2(x: Option<u8>) -> Option<u8> {
x

40
src/test/codegen/scalar-pair-bool.rs Normal file
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@ -0,0 +1,40 @@
// Copyright 2018 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.
// compile-flags: -O
#![crate_type = "lib"]
// CHECK: define { i8, i8 } @pair_bool_bool(i1 zeroext %pair.0, i1 zeroext %pair.1)
#[no_mangle]
pub fn pair_bool_bool(pair: (bool, bool)) -> (bool, bool) {
pair
}
// CHECK: define { i8, i32 } @pair_bool_i32(i1 zeroext %pair.0, i32 %pair.1)
#[no_mangle]
pub fn pair_bool_i32(pair: (bool, i32)) -> (bool, i32) {
pair
}
// CHECK: define { i32, i8 } @pair_i32_bool(i32 %pair.0, i1 zeroext %pair.1)
#[no_mangle]
pub fn pair_i32_bool(pair: (i32, bool)) -> (i32, bool) {
pair
}
// CHECK: define { i8, i8 } @pair_and_or(i1 zeroext %arg0.0, i1 zeroext %arg0.1)
#[no_mangle]
pub fn pair_and_or((a, b): (bool, bool)) -> (bool, bool) {
// Make sure it can operate directly on the unpacked args
// CHECK: and i1 %arg0.0, %arg0.1
// CHECK: or i1 %arg0.0, %arg0.1
(a && b, a || b)
}