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Auto merge of #126578 - scottmcm:inlining-bonuses-too, r=davidtwco 

Account for things that optimize out in inlining costs

This updates the MIR inlining `CostChecker` to have both bonuses and penalties, rather than just penalties.

That lets us add bonuses for some things where we want to encourage inlining without risking wrapping into a gigantic cost.  For example, `switchInt(const …)` we give an inlining bonus because codegen will actually eliminate the branch (and associated dead blocks) once it's monomorphized, so measuring both sides of the branch gives an unrealistically-high cost to it.  Similarly, an `unreachable` terminator gets a small bonus, because whatever branch leads there doesn't actually exist post-codegen.
This commit is contained in:
bors 2024-06-21 02:06:27 +00:00
parent a9c8887c7d eac6b2910a
commit 7a08f84627
8 changed files with 371 additions and 77 deletions
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106
compiler/rustc_mir_transform/src/cost_checker.rs
View File

@ -1,3 +1,4 @@
use rustc_middle::bug;
use rustc_middle::mir::visit::*;
use rustc_middle::mir::*;
use rustc_middle::ty::{self, ParamEnv, Ty, TyCtxt};
@ -6,13 +7,16 @@ const INSTR_COST: usize = 5;
const CALL_PENALTY: usize = 25;
const LANDINGPAD_PENALTY: usize = 50;
const RESUME_PENALTY: usize = 45;
const LARGE_SWITCH_PENALTY: usize = 20;
const CONST_SWITCH_BONUS: usize = 10;
/// Verify that the callee body is compatible with the caller.
#[derive(Clone)]
pub(crate) struct CostChecker<'b, 'tcx> {
tcx: TyCtxt<'tcx>,
param_env: ParamEnv<'tcx>,
cost: usize,
penalty: usize,
bonus: usize,
callee_body: &'b Body<'tcx>,
instance: Option<ty::Instance<'tcx>>,
}
@ -24,11 +28,11 @@ impl<'b, 'tcx> CostChecker<'b, 'tcx> {
instance: Option<ty::Instance<'tcx>>,
callee_body: &'b Body<'tcx>,
) -> CostChecker<'b, 'tcx> {
CostChecker { tcx, param_env, callee_body, instance, cost: 0 }
CostChecker { tcx, param_env, callee_body, instance, penalty: 0, bonus: 0 }
}
pub fn cost(&self) -> usize {
self.cost
usize::saturating_sub(self.penalty, self.bonus)
}
fn instantiate_ty(&self, v: Ty<'tcx>) -> Ty<'tcx> {
@ -41,36 +45,49 @@ impl<'b, 'tcx> CostChecker<'b, 'tcx> {
}
impl<'tcx> Visitor<'tcx> for CostChecker<'_, 'tcx> {
fn visit_statement(&mut self, statement: &Statement<'tcx>, _: Location) {
// Don't count StorageLive/StorageDead in the inlining cost.
fn visit_statement(&mut self, statement: &Statement<'tcx>, location: Location) {
// Most costs are in rvalues and terminators, not in statements.
match statement.kind {
StatementKind::StorageLive(_)
| StatementKind::StorageDead(_)
| StatementKind::Deinit(_)
| StatementKind::Nop => {}
_ => self.cost += INSTR_COST,
StatementKind::Intrinsic(ref ndi) => {
self.penalty += match **ndi {
NonDivergingIntrinsic::Assume(..) => INSTR_COST,
NonDivergingIntrinsic::CopyNonOverlapping(..) => CALL_PENALTY,
};
}
_ => self.super_statement(statement, location),
}
}
fn visit_rvalue(&mut self, rvalue: &Rvalue<'tcx>, _location: Location) {
match rvalue {
Rvalue::NullaryOp(NullOp::UbChecks, ..) if !self.tcx.sess.ub_checks() => {
// If this is in optimized MIR it's because it's used later,
// so if we don't need UB checks this session, give a bonus
// here to offset the cost of the call later.
self.bonus += CALL_PENALTY;
}
// These are essentially constants that didn't end up in an Operand,
// so treat them as also being free.
Rvalue::NullaryOp(..) => {}
_ => self.penalty += INSTR_COST,
}
}
fn visit_terminator(&mut self, terminator: &Terminator<'tcx>, _: Location) {
let tcx = self.tcx;
match terminator.kind {
TerminatorKind::Drop { ref place, unwind, .. } => {
match &terminator.kind {
TerminatorKind::Drop { place, unwind, .. } => {
// If the place doesn't actually need dropping, treat it like a regular goto.
let ty = self.instantiate_ty(place.ty(self.callee_body, tcx).ty);
if ty.needs_drop(tcx, self.param_env) {
self.cost += CALL_PENALTY;
let ty = self.instantiate_ty(place.ty(self.callee_body, self.tcx).ty);
if ty.needs_drop(self.tcx, self.param_env) {
self.penalty += CALL_PENALTY;
if let UnwindAction::Cleanup(_) = unwind {
self.cost += LANDINGPAD_PENALTY;
self.penalty += LANDINGPAD_PENALTY;
}
} else {
self.cost += INSTR_COST;
}
}
TerminatorKind::Call { func: Operand::Constant(ref f), unwind, .. } => {
let fn_ty = self.instantiate_ty(f.const_.ty());
self.cost += if let ty::FnDef(def_id, _) = *fn_ty.kind()
&& tcx.intrinsic(def_id).is_some()
TerminatorKind::Call { func, unwind, .. } => {
self.penalty += if let Some((def_id, ..)) = func.const_fn_def()
&& self.tcx.intrinsic(def_id).is_some()
{
// Don't give intrinsics the extra penalty for calls
INSTR_COST
@ -78,23 +95,50 @@ impl<'tcx> Visitor<'tcx> for CostChecker<'_, 'tcx> {
CALL_PENALTY
};
if let UnwindAction::Cleanup(_) = unwind {
self.cost += LANDINGPAD_PENALTY;
self.penalty += LANDINGPAD_PENALTY;
}
}
TerminatorKind::Assert { unwind, .. } => {
self.cost += CALL_PENALTY;
TerminatorKind::SwitchInt { discr, targets } => {
if discr.constant().is_some() {
// Not only will this become a `Goto`, but likely other
// things will be removable as unreachable.
self.bonus += CONST_SWITCH_BONUS;
} else if targets.all_targets().len() > 3 {
// More than false/true/unreachable gets extra cost.
self.penalty += LARGE_SWITCH_PENALTY;
} else {
self.penalty += INSTR_COST;
}
}
TerminatorKind::Assert { unwind, msg, .. } => {
self.penalty +=
if msg.is_optional_overflow_check() && !self.tcx.sess.overflow_checks() {
INSTR_COST
} else {
CALL_PENALTY
};
if let UnwindAction::Cleanup(_) = unwind {
self.cost += LANDINGPAD_PENALTY;
self.penalty += LANDINGPAD_PENALTY;
}
}
TerminatorKind::UnwindResume => self.cost += RESUME_PENALTY,
TerminatorKind::UnwindResume => self.penalty += RESUME_PENALTY,
TerminatorKind::InlineAsm { unwind, .. } => {
self.cost += INSTR_COST;
self.penalty += INSTR_COST;
if let UnwindAction::Cleanup(_) = unwind {
self.cost += LANDINGPAD_PENALTY;
self.penalty += LANDINGPAD_PENALTY;
}
}
_ => self.cost += INSTR_COST,
TerminatorKind::Unreachable => {
self.bonus += INSTR_COST;
}
TerminatorKind::Goto { .. } | TerminatorKind::Return => {}
TerminatorKind::UnwindTerminate(..) => {}
kind @ (TerminatorKind::FalseUnwind { .. }
| TerminatorKind::FalseEdge { .. }
| TerminatorKind::Yield { .. }
| TerminatorKind::CoroutineDrop) => {
bug!("{kind:?} should not be in runtime MIR");
}
}
}
}

6
library/core/src/slice/iter/macros.rs
View File

@ -103,7 +103,8 @@ macro_rules! iterator {
// so this new pointer is inside `self` and thus guaranteed to be non-null.
unsafe {
if_zst!(mut self,
len => *len = len.unchecked_sub(offset),
// Using the intrinsic directly avoids emitting a UbCheck
len => *len = crate::intrinsics::unchecked_sub(*len, offset),
_end => self.ptr = self.ptr.add(offset),
);
}
@ -119,7 +120,8 @@ macro_rules! iterator {
// SAFETY: By our precondition, `offset` can be at most the
// current length, so the subtraction can never overflow.
len => unsafe {
*len = len.unchecked_sub(offset);
// Using the intrinsic directly avoids emitting a UbCheck
*len = crate::intrinsics::unchecked_sub(*len, offset);
self.ptr
},
// SAFETY: the caller guarantees that `offset` doesn't exceed `self.len()`,

6
tests/codegen/issues/issue-112509-slice-get-andthen-get.rs
View File

@ -3,8 +3,12 @@
// CHECK-LABEL: @write_u8_variant_a
// CHECK-NEXT: {{.*}}:
// CHECK-NEXT: getelementptr
// CHECK-NEXT: icmp ugt
// CHECK-NEXT: getelementptr
// CHECK-NEXT: select i1 {{.+}} null
// CHECK-NEXT: insertvalue
// CHECK-NEXT: insertvalue
// CHECK-NEXT: ret
#[no_mangle]
pub fn write_u8_variant_a(bytes: &mut [u8], buf: u8, offset: usize) -> Option<&mut [u8]> {
let buf = buf.to_le_bytes();

4
tests/crashes/123893.rs
View File

@ -11,6 +11,7 @@ fn generic_impl<T>() {
impl<T> MagicTrait for T {
const IS_BIG: bool = true;
}
more_cost();
if T::IS_BIG {
big_impl::<i32>();
}
@ -18,3 +19,6 @@ fn generic_impl<T>() {
#[inline(never)]
fn big_impl<T>() {}
#[inline(never)]
fn more_cost() {}

77
tests/mir-opt/pre-codegen/checked_ops.step_forward.PreCodegen.after.panic-abort.mir
View File

@ -4,12 +4,87 @@ fn step_forward(_1: u16, _2: usize) -> u16 {
debug x => _1;
debug n => _2;
let mut _0: u16;
scope 1 (inlined <u16 as Step>::forward) {
let mut _8: u16;
scope 2 {
}
scope 3 (inlined <u16 as Step>::forward_checked) {
scope 4 {
scope 6 (inlined core::num::<impl u16>::checked_add) {
let mut _7: bool;
scope 7 {
}
scope 8 (inlined core::num::<impl u16>::overflowing_add) {
let mut _5: (u16, bool);
let _6: bool;
scope 9 {
}
}
}
}
scope 5 (inlined convert::num::ptr_try_from_impls::<impl TryFrom<usize> for u16>::try_from) {
let mut _3: bool;
let mut _4: u16;
}
}
scope 10 (inlined Option::<u16>::is_none) {
scope 11 (inlined Option::<u16>::is_some) {
}
}
scope 12 (inlined core::num::<impl u16>::wrapping_add) {
}
}
bb0: {
_0 = <u16 as Step>::forward(move _1, move _2) -> [return: bb1, unwind unreachable];
StorageLive(_4);
StorageLive(_3);
_3 = Gt(_2, const 65535_usize);
switchInt(move _3) -> [0: bb1, otherwise: bb5];
}
bb1: {
_4 = _2 as u16 (IntToInt);
StorageDead(_3);
StorageLive(_6);
StorageLive(_5);
_5 = AddWithOverflow(_1, _4);
_6 = (_5.1: bool);
StorageDead(_5);
StorageLive(_7);
_7 = unlikely(move _6) -> [return: bb2, unwind unreachable];
}
bb2: {
switchInt(move _7) -> [0: bb3, otherwise: bb4];
}
bb3: {
StorageDead(_7);
StorageDead(_6);
goto -> bb7;
}
bb4: {
StorageDead(_7);
StorageDead(_6);
goto -> bb6;
}
bb5: {
StorageDead(_3);
goto -> bb6;
}
bb6: {
assert(!const true, "attempt to compute `{} + {}`, which would overflow", const core::num::<impl u16>::MAX, const 1_u16) -> [success: bb7, unwind unreachable];
}
bb7: {
StorageLive(_8);
_8 = _2 as u16 (IntToInt);
_0 = Add(_1, _8);
StorageDead(_8);
StorageDead(_4);
return;
}
}

77
tests/mir-opt/pre-codegen/checked_ops.step_forward.PreCodegen.after.panic-unwind.mir
View File

@ -4,12 +4,87 @@ fn step_forward(_1: u16, _2: usize) -> u16 {
debug x => _1;
debug n => _2;
let mut _0: u16;
scope 1 (inlined <u16 as Step>::forward) {
let mut _8: u16;
scope 2 {
}
scope 3 (inlined <u16 as Step>::forward_checked) {
scope 4 {
scope 6 (inlined core::num::<impl u16>::checked_add) {
let mut _7: bool;
scope 7 {
}
scope 8 (inlined core::num::<impl u16>::overflowing_add) {
let mut _5: (u16, bool);
let _6: bool;
scope 9 {
}
}
}
}
scope 5 (inlined convert::num::ptr_try_from_impls::<impl TryFrom<usize> for u16>::try_from) {
let mut _3: bool;
let mut _4: u16;
}
}
scope 10 (inlined Option::<u16>::is_none) {
scope 11 (inlined Option::<u16>::is_some) {
}
}
scope 12 (inlined core::num::<impl u16>::wrapping_add) {
}
}
bb0: {
_0 = <u16 as Step>::forward(move _1, move _2) -> [return: bb1, unwind continue];
StorageLive(_4);
StorageLive(_3);
_3 = Gt(_2, const 65535_usize);
switchInt(move _3) -> [0: bb1, otherwise: bb5];
}
bb1: {
_4 = _2 as u16 (IntToInt);
StorageDead(_3);
StorageLive(_6);
StorageLive(_5);
_5 = AddWithOverflow(_1, _4);
_6 = (_5.1: bool);
StorageDead(_5);
StorageLive(_7);
_7 = unlikely(move _6) -> [return: bb2, unwind unreachable];
}
bb2: {
switchInt(move _7) -> [0: bb3, otherwise: bb4];
}
bb3: {
StorageDead(_7);
StorageDead(_6);
goto -> bb7;
}
bb4: {
StorageDead(_7);
StorageDead(_6);
goto -> bb6;
}
bb5: {
StorageDead(_3);
goto -> bb6;
}
bb6: {
assert(!const true, "attempt to compute `{} + {}`, which would overflow", const core::num::<impl u16>::MAX, const 1_u16) -> [success: bb7, unwind continue];
}
bb7: {
StorageLive(_8);
_8 = _2 as u16 (IntToInt);
_0 = Add(_1, _8);
StorageDead(_8);
StorageDead(_4);
return;
}
}

79
tests/mir-opt/pre-codegen/loops.mapped.PreCodegen.after.mir
View File

@ -7,14 +7,30 @@ fn mapped(_1: impl Iterator<Item = T>, _2: impl Fn(T) -> U) -> () {
let mut _3: std::iter::Map<impl Iterator<Item = T>, impl Fn(T) -> U>;
let mut _4: std::iter::Map<impl Iterator<Item = T>, impl Fn(T) -> U>;
let mut _5: &mut std::iter::Map<impl Iterator<Item = T>, impl Fn(T) -> U>;
let mut _6: std::option::Option<U>;
let mut _7: isize;
let _9: ();
let mut _13: std::option::Option<U>;
let _15: ();
scope 1 {
debug iter => _4;
let _8: U;
let _14: U;
scope 2 {
debug x => _8;
debug x => _14;
}
scope 4 (inlined <Map<impl Iterator<Item = T>, impl Fn(T) -> U> as Iterator>::next) {
debug self => _5;
let mut _6: &mut impl Iterator<Item = T>;
let mut _7: std::option::Option<T>;
let mut _8: &mut impl Fn(T) -> U;
scope 5 (inlined Option::<T>::map::<U, &mut impl Fn(T) -> U>) {
debug self => _7;
debug f => _8;
let mut _9: isize;
let _10: T;
let mut _11: (T,);
let mut _12: U;
scope 6 {
debug x => _10;
}
}
}
}
scope 3 (inlined <Map<impl Iterator<Item = T>, impl Fn(T) -> U> as IntoIterator>::into_iter) {
@ -32,20 +48,30 @@ fn mapped(_1: impl Iterator<Item = T>, _2: impl Fn(T) -> U) -> () {
}
bb2: {
StorageLive(_6);
StorageLive(_5);
StorageLive(_13);
_5 = &mut _4;
_6 = <Map<impl Iterator<Item = T>, impl Fn(T) -> U> as Iterator>::next(move _5) -> [return: bb3, unwind: bb9];
StorageLive(_8);
StorageLive(_7);
StorageLive(_6);
_6 = &mut (_4.0: impl Iterator<Item = T>);
_7 = <impl Iterator<Item = T> as Iterator>::next(move _6) -> [return: bb3, unwind: bb10];
}
bb3: {
StorageDead(_5);
_7 = discriminant(_6);
switchInt(move _7) -> [0: bb4, 1: bb6, otherwise: bb8];
StorageDead(_6);
_8 = &mut (_4.1: impl Fn(T) -> U);
StorageLive(_9);
StorageLive(_10);
_9 = discriminant(_7);
switchInt(move _9) -> [0: bb4, 1: bb6, otherwise: bb9];
}
bb4: {
StorageDead(_6);
StorageDead(_10);
StorageDead(_9);
StorageDead(_7);
StorageDead(_8);
StorageDead(_13);
drop(_4) -> [return: bb5, unwind continue];
}
@ -55,24 +81,39 @@ fn mapped(_1: impl Iterator<Item = T>, _2: impl Fn(T) -> U) -> () {
}
bb6: {
_8 = move ((_6 as Some).0: U);
_9 = opaque::<U>(move _8) -> [return: bb7, unwind: bb9];
_10 = move ((_7 as Some).0: T);
StorageLive(_12);
StorageLive(_11);
_11 = (_10,);
_12 = <&mut impl Fn(T) -> U as FnOnce<(T,)>>::call_once(move _8, move _11) -> [return: bb7, unwind: bb10];
}
bb7: {
StorageDead(_6);
goto -> bb2;
StorageDead(_11);
_13 = Option::<U>::Some(move _12);
StorageDead(_12);
StorageDead(_10);
StorageDead(_9);
StorageDead(_7);
StorageDead(_8);
_14 = move ((_13 as Some).0: U);
_15 = opaque::<U>(move _14) -> [return: bb8, unwind: bb10];
}
bb8: {
StorageDead(_13);
goto -> bb2;
}
bb9: {
unreachable;
}
bb9 (cleanup): {
drop(_4) -> [return: bb10, unwind terminate(cleanup)];
bb10 (cleanup): {
drop(_4) -> [return: bb11, unwind terminate(cleanup)];
}
bb10 (cleanup): {
bb11 (cleanup): {
resume;
}
}

93
tests/mir-opt/pre-codegen/slice_iter.enumerated_loop.PreCodegen.after.panic-abort.mir
View File

@ -7,19 +7,44 @@ fn enumerated_loop(_1: &[T], _2: impl Fn(usize, &T)) -> () {
let mut _11: std::slice::Iter<'_, T>;
let mut _12: std::iter::Enumerate<std::slice::Iter<'_, T>>;
let mut _13: std::iter::Enumerate<std::slice::Iter<'_, T>>;
let mut _14: &mut std::iter::Enumerate<std::slice::Iter<'_, T>>;
let mut _15: std::option::Option<(usize, &T)>;
let mut _16: isize;
let mut _19: &impl Fn(usize, &T);
let mut _20: (usize, &T);
let _21: ();
let mut _21: std::option::Option<(usize, &T)>;
let mut _24: &impl Fn(usize, &T);
let mut _25: (usize, &T);
let _26: ();
scope 1 {
debug iter => _13;
let _17: usize;
let _18: &T;
let _22: usize;
let _23: &T;
scope 2 {
debug i => _17;
debug x => _18;
debug i => _22;
debug x => _23;
}
scope 17 (inlined <Enumerate<std::slice::Iter<'_, T>> as Iterator>::next) {
let mut _14: &mut std::slice::Iter<'_, T>;
let mut _15: std::option::Option<&T>;
let mut _19: (usize, bool);
let mut _20: (usize, &T);
scope 18 {
let _18: usize;
scope 23 {
}
}
scope 19 {
scope 20 {
scope 26 (inlined <Option<(usize, &T)> as FromResidual>::from_residual) {
}
}
}
scope 21 {
scope 22 {
}
}
scope 24 (inlined <Option<&T> as Try>::branch) {
let mut _16: isize;
let _17: &T;
scope 25 {
}
}
}
}
scope 3 (inlined core::slice::<impl [T]>::iter) {
@ -107,20 +132,28 @@ fn enumerated_loop(_1: &[T], _2: impl Fn(usize, &T)) -> () {
}
bb4: {
StorageLive(_21);
StorageLive(_18);
StorageLive(_19);
StorageLive(_15);
StorageLive(_14);
_14 = &mut _13;
_15 = <Enumerate<std::slice::Iter<'_, T>> as Iterator>::next(move _14) -> [return: bb5, unwind unreachable];
_14 = &mut (_13.0: std::slice::Iter<'_, T>);
_15 = <std::slice::Iter<'_, T> as Iterator>::next(move _14) -> [return: bb5, unwind unreachable];
}
bb5: {
StorageDead(_14);
StorageLive(_16);
_16 = discriminant(_15);
switchInt(move _16) -> [0: bb6, 1: bb8, otherwise: bb10];
switchInt(move _16) -> [0: bb6, 1: bb8, otherwise: bb11];
}
bb6: {
StorageDead(_16);
StorageDead(_15);
StorageDead(_19);
StorageDead(_18);
StorageDead(_21);
StorageDead(_13);
drop(_2) -> [return: bb7, unwind unreachable];
}
@ -130,23 +163,39 @@ fn enumerated_loop(_1: &[T], _2: impl Fn(usize, &T)) -> () {
}
bb8: {
_17 = (((_15 as Some).0: (usize, &T)).0: usize);
_18 = (((_15 as Some).0: (usize, &T)).1: &T);
StorageLive(_19);
_19 = &_2;
StorageLive(_20);
_20 = (_17, _18);
_21 = <impl Fn(usize, &T) as Fn<(usize, &T)>>::call(move _19, move _20) -> [return: bb9, unwind unreachable];
_17 = move ((_15 as Some).0: &T);
StorageDead(_16);
StorageDead(_15);
_18 = (_13.1: usize);
_19 = AddWithOverflow((_13.1: usize), const 1_usize);
assert(!move (_19.1: bool), "attempt to compute `{} + {}`, which would overflow", (_13.1: usize), const 1_usize) -> [success: bb9, unwind unreachable];
}
bb9: {
(_13.1: usize) = move (_19.0: usize);
StorageLive(_20);
_20 = (_18, _17);
_21 = Option::<(usize, &T)>::Some(move _20);
StorageDead(_20);
StorageDead(_19);
StorageDead(_15);
goto -> bb4;
StorageDead(_18);
_22 = (((_21 as Some).0: (usize, &T)).0: usize);
_23 = (((_21 as Some).0: (usize, &T)).1: &T);
StorageLive(_24);
_24 = &_2;
StorageLive(_25);
_25 = (_22, _23);
_26 = <impl Fn(usize, &T) as Fn<(usize, &T)>>::call(move _24, move _25) -> [return: bb10, unwind unreachable];
}
bb10: {
StorageDead(_25);
StorageDead(_24);
StorageDead(_21);
goto -> bb4;
}
bb11: {
unreachable;
}
}