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[mir-inlining] Count &T ↔ *const T conversions as free #123843

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[mir-inlining] Count &T ↔ *const T conversions as free #123843

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d816e32
Add a MIR pre-codegen test for Vec::deref
scottmcm Mar 29, 2024
2e76831
Count `&T` ↔ `*const T` conversions as free in inlining
scottmcm Apr 12, 2024
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13 changes: 12 additions & 1 deletion compiler/rustc_mir_transform/src/cost_checker.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -40,14 +40,25 @@ impl<'b, 'tcx> CostChecker<'b, 'tcx> {
}
}

fn rvalue_is_nop(rvalue: &Rvalue<'_>) -> bool {
match rvalue {
// Treat `&*pointer` and `addr_of!(*reference)` as free when inlining
Rvalue::Ref(_, _, place) | Rvalue::AddressOf(_, place) => {
**place.projection == [PlaceElem::Deref]
}
_ => false,
}
}

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.
match statement.kind {
match &statement.kind {
StatementKind::StorageLive(_)
| StatementKind::StorageDead(_)
| StatementKind::Deinit(_)
| StatementKind::Nop => {}
StatementKind::Assign(place_and_rvalue) if rvalue_is_nop(&place_and_rvalue.1) => {}
_ => self.cost += INSTR_COST,
}
}
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13 changes: 13 additions & 0 deletions tests/mir-opt/pre-codegen/vec_deref.rs
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@@ -0,0 +1,13 @@
// skip-filecheck
//@ compile-flags: -O -Zmir-opt-level=2 -Cdebuginfo=2
// EMIT_MIR_FOR_EACH_PANIC_STRATEGY

#![crate_type = "lib"]

// Added after it stopped inlining in a nightly; see
// <https://github.com/rust-lang/rust/issues/123174>

// EMIT_MIR vec_deref.vec_deref_to_slice.PreCodegen.after.mir
pub fn vec_deref_to_slice(v: &Vec<u8>) -> &[u8] {
v
}
80 changes: 80 additions & 0 deletions tests/mir-opt/pre-codegen/vec_deref.vec_deref_to_slice.PreCodegen.after.panic-abort.mir
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@@ -0,0 +1,80 @@
// MIR for `vec_deref_to_slice` after PreCodegen

fn vec_deref_to_slice(_1: &Vec<u8>) -> &[u8] {
debug v => _1;
let mut _0: &[u8];
scope 1 (inlined <Vec<u8> as Deref>::deref) {
debug self => _1;
let mut _4: *const u8;
let mut _5: usize;
scope 2 (inlined Vec::<u8>::as_ptr) {
debug self => _1;
let mut _2: &alloc::raw_vec::RawVec<u8>;
scope 3 (inlined alloc::raw_vec::RawVec::<u8>::ptr) {
debug self => _2;
let mut _3: std::ptr::NonNull<u8>;
scope 4 (inlined Unique::<u8>::as_ptr) {
debug ((self: Unique<u8>).0: std::ptr::NonNull<u8>) => _3;
debug ((self: Unique<u8>).1: std::marker::PhantomData<u8>) => const PhantomData::<u8>;
scope 5 (inlined NonNull::<u8>::as_ptr) {
debug self => _3;
}
}
}
}
scope 6 (inlined std::slice::from_raw_parts::<'_, u8>) {
debug data => _4;
debug len => _5;
let _9: *const [u8];
scope 7 (inlined core::ub_checks::check_language_ub) {
scope 8 (inlined core::ub_checks::check_language_ub::runtime) {
}
}
scope 9 (inlined std::mem::size_of::<u8>) {
}
scope 10 (inlined align_of::<u8>) {
}
scope 11 (inlined slice_from_raw_parts::<u8>) {
debug data => _4;
debug len => _5;
let mut _6: *const ();
scope 12 (inlined std::ptr::const_ptr::<impl *const u8>::cast::<()>) {
debug self => _4;
}
scope 13 (inlined std::ptr::from_raw_parts::<[u8]>) {
debug data_pointer => _6;
debug metadata => _5;
let mut _7: std::ptr::metadata::PtrComponents<[u8]>;
let mut _8: std::ptr::metadata::PtrRepr<[u8]>;
}
}
}
}

bb0: {
StorageLive(_4);
StorageLive(_2);
_2 = &((*_1).0: alloc::raw_vec::RawVec<u8>);
StorageLive(_3);
_3 = ((((*_1).0: alloc::raw_vec::RawVec<u8>).0: std::ptr::Unique<u8>).0: std::ptr::NonNull<u8>);
_4 = (_3.0: *const u8);
StorageDead(_3);
StorageDead(_2);
StorageLive(_5);
_5 = ((*_1).1: usize);
StorageLive(_6);
_6 = _4 as *const () (PtrToPtr);
StorageLive(_8);
StorageLive(_7);
_7 = std::ptr::metadata::PtrComponents::<[u8]> { data_pointer: _6, metadata: _5 };
_8 = std::ptr::metadata::PtrRepr::<[u8]> { const_ptr: move _7 };
StorageDead(_7);
_9 = (_8.0: *const [u8]);
StorageDead(_8);
StorageDead(_6);
StorageDead(_5);
StorageDead(_4);
_0 = &(*_9);
return;
}
}
80 changes: 80 additions & 0 deletions tests/mir-opt/pre-codegen/vec_deref.vec_deref_to_slice.PreCodegen.after.panic-unwind.mir
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Original file line number Diff line number Diff line change
@@ -0,0 +1,80 @@
// MIR for `vec_deref_to_slice` after PreCodegen

fn vec_deref_to_slice(_1: &Vec<u8>) -> &[u8] {
debug v => _1;
let mut _0: &[u8];
scope 1 (inlined <Vec<u8> as Deref>::deref) {
debug self => _1;
let mut _4: *const u8;
let mut _5: usize;
scope 2 (inlined Vec::<u8>::as_ptr) {
debug self => _1;
let mut _2: &alloc::raw_vec::RawVec<u8>;
scope 3 (inlined alloc::raw_vec::RawVec::<u8>::ptr) {
debug self => _2;
let mut _3: std::ptr::NonNull<u8>;
scope 4 (inlined Unique::<u8>::as_ptr) {
debug ((self: Unique<u8>).0: std::ptr::NonNull<u8>) => _3;
debug ((self: Unique<u8>).1: std::marker::PhantomData<u8>) => const PhantomData::<u8>;
scope 5 (inlined NonNull::<u8>::as_ptr) {
debug self => _3;
}
}
}
}
scope 6 (inlined std::slice::from_raw_parts::<'_, u8>) {
debug data => _4;
debug len => _5;
let _9: *const [u8];
scope 7 (inlined core::ub_checks::check_language_ub) {
scope 8 (inlined core::ub_checks::check_language_ub::runtime) {
}
}
scope 9 (inlined std::mem::size_of::<u8>) {
}
scope 10 (inlined align_of::<u8>) {
}
scope 11 (inlined slice_from_raw_parts::<u8>) {
debug data => _4;
debug len => _5;
let mut _6: *const ();
scope 12 (inlined std::ptr::const_ptr::<impl *const u8>::cast::<()>) {
debug self => _4;
}
scope 13 (inlined std::ptr::from_raw_parts::<[u8]>) {
debug data_pointer => _6;
debug metadata => _5;
let mut _7: std::ptr::metadata::PtrComponents<[u8]>;
let mut _8: std::ptr::metadata::PtrRepr<[u8]>;
}
}
}
}

bb0: {
StorageLive(_4);
StorageLive(_2);
_2 = &((*_1).0: alloc::raw_vec::RawVec<u8>);
StorageLive(_3);
_3 = ((((*_1).0: alloc::raw_vec::RawVec<u8>).0: std::ptr::Unique<u8>).0: std::ptr::NonNull<u8>);
_4 = (_3.0: *const u8);
StorageDead(_3);
StorageDead(_2);
StorageLive(_5);
_5 = ((*_1).1: usize);
StorageLive(_6);
_6 = _4 as *const () (PtrToPtr);
StorageLive(_8);
StorageLive(_7);
_7 = std::ptr::metadata::PtrComponents::<[u8]> { data_pointer: _6, metadata: _5 };
_8 = std::ptr::metadata::PtrRepr::<[u8]> { const_ptr: move _7 };
StorageDead(_7);
_9 = (_8.0: *const [u8]);
StorageDead(_8);
StorageDead(_6);
StorageDead(_5);
StorageDead(_4);
_0 = &(*_9);
return;
}
}
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