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Auto merge of #110705 - saethlin:ignore-locals-cost, r=cjgillot
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Remove the size of locals heuristic in MIR inlining

This heuristic doesn't necessarily correlate to complexity of the MIR Body. In particular, a lot of straight-line code in MIR tends to never reuse a local, even though any optimizer would effectively reuse the storage or just put everything in registers. So it doesn't even necessarily make sense that this would be a stack size heuristic.

So... what happens if we just delete the heuristic? The benchmark suite improves significantly. Less heuristics better?

r? `@cjgillot`
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@bors
bors committed Apr 23, 2023
2 parents 3462f79 + 173845c commit 915aa06
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Showing 5 changed files with 450 additions and 82 deletions.
34 changes: 0 additions & 34 deletions compiler/rustc_mir_transform/src/inline.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -26,8 +26,6 @@ const CALL_PENALTY: usize = 25;
const LANDINGPAD_PENALTY: usize = 50;
const RESUME_PENALTY: usize = 45;

const UNKNOWN_SIZE_COST: usize = 10;

const TOP_DOWN_DEPTH_LIMIT: usize = 5;

pub struct Inline;
Expand Down Expand Up @@ -464,12 +462,6 @@ impl<'tcx> Inliner<'tcx> {
}
}

// Count up the cost of local variables and temps, if we know the size
// use that, otherwise we use a moderately-large dummy cost.
for v in callee_body.vars_and_temps_iter() {
checker.visit_local_decl(v, &callee_body.local_decls[v]);
}

// Abort if type validation found anything fishy.
checker.validation?;

Expand Down Expand Up @@ -764,14 +756,6 @@ impl<'tcx> Inliner<'tcx> {
}
}

fn type_size_of<'tcx>(
tcx: TyCtxt<'tcx>,
param_env: ty::ParamEnv<'tcx>,
ty: Ty<'tcx>,
) -> Option<u64> {
tcx.layout_of(param_env.and(ty)).ok().map(|layout| layout.size.bytes())
}

/// Verify that the callee body is compatible with the caller.
///
/// This visitor mostly computes the inlining cost,
Expand Down Expand Up @@ -845,24 +829,6 @@ impl<'tcx> Visitor<'tcx> for CostChecker<'_, 'tcx> {
self.super_terminator(terminator, location);
}

/// Count up the cost of local variables and temps, if we know the size
/// use that, otherwise we use a moderately-large dummy cost.
fn visit_local_decl(&mut self, local: Local, local_decl: &LocalDecl<'tcx>) {
let tcx = self.tcx;
let ptr_size = tcx.data_layout.pointer_size.bytes();

let ty = self.instance.subst_mir(tcx, &local_decl.ty);
// Cost of the var is the size in machine-words, if we know
// it.
if let Some(size) = type_size_of(tcx, self.param_env, ty) {
self.cost += ((size + ptr_size - 1) / ptr_size) as usize;
} else {
self.cost += UNKNOWN_SIZE_COST;
}

self.super_local_decl(local, local_decl)
}

/// This method duplicates code from MIR validation in an attempt to detect type mismatches due
/// to normalization failure.
fn visit_projection_elem(
Expand Down
129 changes: 115 additions & 14 deletions tests/mir-opt/inline/unchecked_shifts.unchecked_shl_unsigned_smaller.Inline.diff
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Original file line number Diff line number Diff line change
Expand Up @@ -12,7 +12,51 @@
+ debug rhs => _4; // in scope 1 at $SRC_DIR/core/src/num/uint_macros.rs:LL:COL
+ let mut _5: u16; // in scope 1 at $SRC_DIR/core/src/num/mod.rs:LL:COL
+ let mut _6: (u32,); // in scope 1 at $SRC_DIR/core/src/num/mod.rs:LL:COL
+ let mut _7: u32; // in scope 1 at $SRC_DIR/core/src/num/mod.rs:LL:COL
+ scope 2 {
+ scope 3 (inlined core::num::<impl u16>::unchecked_shl::conv) { // at $SRC_DIR/core/src/num/mod.rs:LL:COL
+ debug x => _7; // in scope 3 at $SRC_DIR/core/src/num/mod.rs:LL:COL
+ let mut _8: std::option::Option<u16>; // in scope 3 at $SRC_DIR/core/src/num/mod.rs:LL:COL
+ let mut _9: std::result::Result<u16, std::num::TryFromIntError>; // in scope 3 at $SRC_DIR/core/src/num/mod.rs:LL:COL
+ scope 4 {
+ scope 5 (inlined <u32 as TryInto<u16>>::try_into) { // at $SRC_DIR/core/src/num/mod.rs:LL:COL
+ debug self => _7; // in scope 5 at $SRC_DIR/core/src/convert/mod.rs:LL:COL
+ scope 6 (inlined convert::num::<impl TryFrom<u32> for u16>::try_from) { // at $SRC_DIR/core/src/convert/mod.rs:LL:COL
+ debug u => _7; // in scope 6 at $SRC_DIR/core/src/convert/num.rs:LL:COL
+ let mut _10: bool; // in scope 6 at $SRC_DIR/core/src/convert/num.rs:LL:COL
+ let mut _11: u32; // in scope 6 at $SRC_DIR/core/src/convert/num.rs:LL:COL
+ let mut _12: u16; // in scope 6 at $SRC_DIR/core/src/convert/num.rs:LL:COL
+ }
+ }
+ scope 7 (inlined Result::<u16, TryFromIntError>::ok) { // at $SRC_DIR/core/src/num/mod.rs:LL:COL
+ debug self => _9; // in scope 7 at $SRC_DIR/core/src/result.rs:LL:COL
+ let mut _13: isize; // in scope 7 at $SRC_DIR/core/src/result.rs:LL:COL
+ let _14: u16; // in scope 7 at $SRC_DIR/core/src/result.rs:LL:COL
+ scope 8 {
+ debug x => _14; // in scope 8 at $SRC_DIR/core/src/result.rs:LL:COL
+ }
+ }
+ scope 9 (inlined #[track_caller] Option::<u16>::unwrap_unchecked) { // at $SRC_DIR/core/src/num/mod.rs:LL:COL
+ debug self => _8; // in scope 9 at $SRC_DIR/core/src/option.rs:LL:COL
+ let mut _15: &std::option::Option<u16>; // in scope 9 at $SRC_DIR/core/src/option.rs:LL:COL
+ let mut _16: isize; // in scope 9 at $SRC_DIR/core/src/option.rs:LL:COL
+ scope 10 {
+ debug val => _5; // in scope 10 at $SRC_DIR/core/src/option.rs:LL:COL
+ }
+ scope 11 {
+ scope 13 (inlined unreachable_unchecked) { // at $SRC_DIR/core/src/option.rs:LL:COL
+ scope 14 {
+ scope 15 (inlined unreachable_unchecked::runtime) { // at $SRC_DIR/core/src/intrinsics.rs:LL:COL
+ }
+ }
+ }
+ }
+ scope 12 (inlined Option::<u16>::is_some) { // at $SRC_DIR/core/src/option.rs:LL:COL
+ debug self => _15; // in scope 12 at $SRC_DIR/core/src/option.rs:LL:COL
+ }
+ }
+ }
+ }
+ }
+ }

Expand All @@ -22,30 +66,87 @@
StorageLive(_4); // scope 0 at $DIR/unchecked_shifts.rs:+1:21: +1:22
_4 = _2; // scope 0 at $DIR/unchecked_shifts.rs:+1:21: +1:22
- _0 = core::num::<impl u16>::unchecked_shl(move _3, move _4) -> bb1; // scope 0 at $DIR/unchecked_shifts.rs:+1:5: +1:23
- // mir::Constant
- // + span: $DIR/unchecked_shifts.rs:11:7: 11:20
- // + literal: Const { ty: unsafe fn(u16, u32) -> u16 {core::num::<impl u16>::unchecked_shl}, val: Value(<ZST>) }
+ StorageLive(_5); // scope 2 at $SRC_DIR/core/src/num/mod.rs:LL:COL
+ StorageLive(_6); // scope 2 at $SRC_DIR/core/src/num/mod.rs:LL:COL
+ _6 = (_4,); // scope 2 at $SRC_DIR/core/src/num/mod.rs:LL:COL
+ _5 = core::num::<impl u16>::unchecked_shl::conv(move (_6.0: u32)) -> bb1; // scope 2 at $SRC_DIR/core/src/num/mod.rs:LL:COL
// mir::Constant
- // + span: $DIR/unchecked_shifts.rs:11:7: 11:20
- // + literal: Const { ty: unsafe fn(u16, u32) -> u16 {core::num::<impl u16>::unchecked_shl}, val: Value(<ZST>) }
+ // + span: $SRC_DIR/core/src/num/mod.rs:LL:COL
+ // + literal: Const { ty: fn(u32) -> u16 {core::num::<impl u16>::unchecked_shl::conv}, val: Value(<ZST>) }
+ StorageLive(_7); // scope 2 at $SRC_DIR/core/src/num/mod.rs:LL:COL
+ _7 = move (_6.0: u32); // scope 2 at $SRC_DIR/core/src/num/mod.rs:LL:COL
+ StorageLive(_8); // scope 4 at $SRC_DIR/core/src/num/mod.rs:LL:COL
+ StorageLive(_9); // scope 4 at $SRC_DIR/core/src/num/mod.rs:LL:COL
+ StorageLive(_10); // scope 6 at $SRC_DIR/core/src/convert/num.rs:LL:COL
+ StorageLive(_11); // scope 6 at $SRC_DIR/core/src/convert/num.rs:LL:COL
+ _11 = const 65535_u32; // scope 6 at $SRC_DIR/core/src/convert/num.rs:LL:COL
+ _10 = Gt(_7, move _11); // scope 6 at $SRC_DIR/core/src/convert/num.rs:LL:COL
+ StorageDead(_11); // scope 6 at $SRC_DIR/core/src/convert/num.rs:LL:COL
+ switchInt(move _10) -> [0: bb3, otherwise: bb2]; // scope 6 at $SRC_DIR/core/src/convert/num.rs:LL:COL
}

bb1: {
+ StorageDead(_6); // scope 2 at $SRC_DIR/core/src/num/mod.rs:LL:COL
+ _0 = unchecked_shl::<u16>(_3, move _5) -> [return: bb2, unwind unreachable]; // scope 2 at $SRC_DIR/core/src/num/uint_macros.rs:LL:COL
+ // mir::Constant
+ // + span: $SRC_DIR/core/src/num/uint_macros.rs:LL:COL
+ // + literal: Const { ty: unsafe extern "rust-intrinsic" fn(u16, u16) -> u16 {unchecked_shl::<u16>}, val: Value(<ZST>) }
+ }
+
+ bb2: {
+ StorageDead(_5); // scope 2 at $SRC_DIR/core/src/num/uint_macros.rs:LL:COL
StorageDead(_4); // scope 0 at $DIR/unchecked_shifts.rs:+1:22: +1:23
StorageDead(_3); // scope 0 at $DIR/unchecked_shifts.rs:+1:22: +1:23
return; // scope 0 at $DIR/unchecked_shifts.rs:+2:2: +2:2
+ }
+
+ bb2: {
+ _9 = Result::<u16, TryFromIntError>::Err(const TryFromIntError(())); // scope 6 at $SRC_DIR/core/src/convert/num.rs:LL:COL
+ // mir::Constant
+ // + span: no-location
+ // + literal: Const { ty: TryFromIntError, val: Value(<ZST>) }
+ goto -> bb4; // scope 6 at $SRC_DIR/core/src/convert/num.rs:LL:COL
+ }
+
+ bb3: {
+ StorageLive(_12); // scope 6 at $SRC_DIR/core/src/convert/num.rs:LL:COL
+ _12 = _7 as u16 (IntToInt); // scope 6 at $SRC_DIR/core/src/convert/num.rs:LL:COL
+ _9 = Result::<u16, TryFromIntError>::Ok(move _12); // scope 6 at $SRC_DIR/core/src/convert/num.rs:LL:COL
+ StorageDead(_12); // scope 6 at $SRC_DIR/core/src/convert/num.rs:LL:COL
+ goto -> bb4; // scope 6 at $SRC_DIR/core/src/convert/num.rs:LL:COL
+ }
+
+ bb4: {
+ StorageDead(_10); // scope 6 at $SRC_DIR/core/src/convert/num.rs:LL:COL
+ StorageLive(_14); // scope 4 at $SRC_DIR/core/src/num/mod.rs:LL:COL
+ _13 = discriminant(_9); // scope 7 at $SRC_DIR/core/src/result.rs:LL:COL
+ switchInt(move _13) -> [0: bb7, 1: bb5, otherwise: bb6]; // scope 7 at $SRC_DIR/core/src/result.rs:LL:COL
+ }
+
+ bb5: {
+ _8 = Option::<u16>::None; // scope 7 at $SRC_DIR/core/src/result.rs:LL:COL
+ goto -> bb8; // scope 7 at $SRC_DIR/core/src/result.rs:LL:COL
+ }
+
+ bb6: {
+ unreachable; // scope 7 at $SRC_DIR/core/src/result.rs:LL:COL
+ }
+
+ bb7: {
+ _14 = move ((_9 as Ok).0: u16); // scope 7 at $SRC_DIR/core/src/result.rs:LL:COL
+ _8 = Option::<u16>::Some(move _14); // scope 8 at $SRC_DIR/core/src/result.rs:LL:COL
+ goto -> bb8; // scope 7 at $SRC_DIR/core/src/result.rs:LL:COL
+ }
+
+ bb8: {
+ StorageDead(_14); // scope 4 at $SRC_DIR/core/src/num/mod.rs:LL:COL
+ StorageDead(_9); // scope 4 at $SRC_DIR/core/src/num/mod.rs:LL:COL
+ StorageLive(_15); // scope 4 at $SRC_DIR/core/src/num/mod.rs:LL:COL
+ _16 = discriminant(_8); // scope 9 at $SRC_DIR/core/src/option.rs:LL:COL
+ switchInt(move _16) -> [1: bb9, otherwise: bb6]; // scope 9 at $SRC_DIR/core/src/option.rs:LL:COL
+ }
+
+ bb9: {
+ _5 = move ((_8 as Some).0: u16); // scope 9 at $SRC_DIR/core/src/option.rs:LL:COL
+ StorageDead(_15); // scope 4 at $SRC_DIR/core/src/num/mod.rs:LL:COL
+ StorageDead(_8); // scope 4 at $SRC_DIR/core/src/num/mod.rs:LL:COL
+ StorageDead(_7); // scope 2 at $SRC_DIR/core/src/num/mod.rs:LL:COL
+ StorageDead(_6); // scope 2 at $SRC_DIR/core/src/num/mod.rs:LL:COL
+ _0 = unchecked_shl::<u16>(_3, move _5) -> [return: bb1, unwind unreachable]; // scope 2 at $SRC_DIR/core/src/num/uint_macros.rs:LL:COL
+ // mir::Constant
+ // + span: $SRC_DIR/core/src/num/uint_macros.rs:LL:COL
+ // + literal: Const { ty: unsafe extern "rust-intrinsic" fn(u16, u16) -> u16 {unchecked_shl::<u16>}, val: Value(<ZST>) }
}
}

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