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At opt-level=0, apply only ABI-affecting attributes to functions
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This should provide a small perf improvement for debug builds,
and should more than cancel out the regression from adding noundef,
which was only significant in debug builds.
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@erikdesjardins
erikdesjardins committed Feb 18, 2022
1 parent 73a7423 commit dcbdc8c
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Showing 2 changed files with 115 additions and 41 deletions.
93 changes: 52 additions & 41 deletions compiler/rustc_codegen_llvm/src/abi.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -13,34 +13,14 @@ use rustc_middle::bug;
use rustc_middle::ty::layout::LayoutOf;
pub use rustc_middle::ty::layout::{FAT_PTR_ADDR, FAT_PTR_EXTRA};
use rustc_middle::ty::Ty;
use rustc_session::config;
use rustc_target::abi::call::ArgAbi;
pub use rustc_target::abi::call::*;
use rustc_target::abi::{self, HasDataLayout, Int};
pub use rustc_target::spec::abi::Abi;

use libc::c_uint;

macro_rules! for_each_kind {
($flags: ident, $f: ident, $($kind: ident),+) => ({
$(if $flags.contains(ArgAttribute::$kind) { $f(llvm::Attribute::$kind) })+
})
}

trait ArgAttributeExt {
fn for_each_kind<F>(&self, f: F)
where
F: FnMut(llvm::Attribute);
}

impl ArgAttributeExt for ArgAttribute {
fn for_each_kind<F>(&self, mut f: F)
where
F: FnMut(llvm::Attribute),
{
for_each_kind!(self, f, NoAlias, NoCapture, NonNull, ReadOnly, InReg, NoUndef)
}
}

pub trait ArgAttributesExt {
fn apply_attrs_to_llfn(&self, idx: AttributePlace, cx: &CodegenCx<'_, '_>, llfn: &Value);
fn apply_attrs_to_callsite(
Expand All @@ -58,10 +38,36 @@ fn should_use_mutable_noalias(cx: &CodegenCx<'_, '_>) -> bool {
cx.tcx.sess.opts.debugging_opts.mutable_noalias.unwrap_or(true)
}

const ABI_AFFECTING_ATTRIBUTES: [(ArgAttribute, llvm::Attribute); 1] =
[(ArgAttribute::InReg, llvm::Attribute::InReg)];

const OPTIMIZATION_ATTRIBUTES: [(ArgAttribute, llvm::Attribute); 5] = [
(ArgAttribute::NoAlias, llvm::Attribute::NoAlias),
(ArgAttribute::NoCapture, llvm::Attribute::NoCapture),
(ArgAttribute::NonNull, llvm::Attribute::NonNull),
(ArgAttribute::ReadOnly, llvm::Attribute::ReadOnly),
(ArgAttribute::NoUndef, llvm::Attribute::NoUndef),
];

impl ArgAttributesExt for ArgAttributes {
fn apply_attrs_to_llfn(&self, idx: AttributePlace, cx: &CodegenCx<'_, '_>, llfn: &Value) {
let mut regular = self.regular;
unsafe {
// ABI-affecting attributes must always be applied
for (attr, llattr) in ABI_AFFECTING_ATTRIBUTES {
if regular.contains(attr) {
llattr.apply_llfn(idx, llfn);
}
}
match self.arg_ext {
ArgExtension::None => {}
ArgExtension::Zext => llvm::Attribute::ZExt.apply_llfn(idx, llfn),
ArgExtension::Sext => llvm::Attribute::SExt.apply_llfn(idx, llfn),
}
// Only apply remaining attributes when optimizing
if cx.sess().opts.optimize == config::OptLevel::No {
return;
}
let deref = self.pointee_size.bytes();
if deref != 0 {
if regular.contains(ArgAttribute::NonNull) {
Expand All @@ -74,19 +80,14 @@ impl ArgAttributesExt for ArgAttributes {
if let Some(align) = self.pointee_align {
llvm::LLVMRustAddAlignmentAttr(llfn, idx.as_uint(), align.bytes() as u32);
}
regular.for_each_kind(|attr| attr.apply_llfn(idx, llfn));
for (attr, llattr) in OPTIMIZATION_ATTRIBUTES {
if regular.contains(attr) {
llattr.apply_llfn(idx, llfn);
}
}
if regular.contains(ArgAttribute::NoAliasMutRef) && should_use_mutable_noalias(cx) {
llvm::Attribute::NoAlias.apply_llfn(idx, llfn);
}
match self.arg_ext {
ArgExtension::None => {}
ArgExtension::Zext => {
llvm::Attribute::ZExt.apply_llfn(idx, llfn);
}
ArgExtension::Sext => {
llvm::Attribute::SExt.apply_llfn(idx, llfn);
}
}
}
}

Expand All @@ -98,6 +99,21 @@ impl ArgAttributesExt for ArgAttributes {
) {
let mut regular = self.regular;
unsafe {
// ABI-affecting attributes must always be applied
for (attr, llattr) in ABI_AFFECTING_ATTRIBUTES {
if regular.contains(attr) {
llattr.apply_callsite(idx, callsite);
}
}
match self.arg_ext {
ArgExtension::None => {}
ArgExtension::Zext => llvm::Attribute::ZExt.apply_callsite(idx, callsite),
ArgExtension::Sext => llvm::Attribute::SExt.apply_callsite(idx, callsite),
}
// Only apply remaining attributes when optimizing
if cx.sess().opts.optimize == config::OptLevel::No {
return;
}
let deref = self.pointee_size.bytes();
if deref != 0 {
if regular.contains(ArgAttribute::NonNull) {
Expand All @@ -118,19 +134,14 @@ impl ArgAttributesExt for ArgAttributes {
align.bytes() as u32,
);
}
regular.for_each_kind(|attr| attr.apply_callsite(idx, callsite));
for (attr, llattr) in OPTIMIZATION_ATTRIBUTES {
if regular.contains(attr) {
llattr.apply_callsite(idx, callsite);
}
}
if regular.contains(ArgAttribute::NoAliasMutRef) && should_use_mutable_noalias(cx) {
llvm::Attribute::NoAlias.apply_callsite(idx, callsite);
}
match self.arg_ext {
ArgExtension::None => {}
ArgExtension::Zext => {
llvm::Attribute::ZExt.apply_callsite(idx, callsite);
}
ArgExtension::Sext => {
llvm::Attribute::SExt.apply_callsite(idx, callsite);
}
}
}
}
}
Expand Down
63 changes: 63 additions & 0 deletions src/test/codegen/function-arguments-noopt.rs
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Original file line number Diff line number Diff line change
@@ -0,0 +1,63 @@
// compile-flags: -C opt-level=0 -C no-prepopulate-passes

// This test checks that arguments/returns in opt-level=0 builds,
// while lacking attributes used for optimization, still have ABI-affecting attributes.

#![crate_type = "lib"]
#![feature(rustc_attrs)]

pub struct S {
_field: [i32; 8],
}

// CHECK: define zeroext i1 @boolean(i1 zeroext %x)
#[no_mangle]
pub fn boolean(x: bool) -> bool {
x
}

// CHECK-LABEL: @boolean_call
#[no_mangle]
pub fn boolean_call(x: bool, f: fn(bool) -> bool) -> bool {
// CHECK: call zeroext i1 %f(i1 zeroext %x)
f(x)
}

// CHECK: define i32* @borrow(i32* %x)
#[no_mangle]
pub fn borrow(x: &i32) -> &i32 {
x
}

// CHECK-LABEL: @borrow_call
#[no_mangle]
pub fn borrow_call(x: &i32, f: fn(&i32) -> &i32) -> &i32 {
// CHECK: call i32* %f(i32* %x)
f(x)
}

// CHECK: define void @struct_(%S* sret(%S){{( %0)?}}, %S* %x)
#[no_mangle]
pub fn struct_(x: S) -> S {
x
}

// CHECK-LABEL: @struct_call
#[no_mangle]
pub fn struct_call(x: S, f: fn(S) -> S) -> S {
// CHECK: call void %f(%S* sret(%S){{( %0)?}}, %S* %{{.+}})
f(x)
}

// CHECK: define { i8, i8 } @enum_(i1 zeroext %x.0, i8 %x.1)
#[no_mangle]
pub fn enum_(x: Option<u8>) -> Option<u8> {
x
}

// CHECK-LABEL: @enum_call
#[no_mangle]
pub fn enum_call(x: Option<u8>, f: fn(Option<u8>) -> Option<u8>) -> Option<u8> {
// CHECK: call { i8, i8 } %f(i1 zeroext %x.0, i8 %x.1)
f(x)
}

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