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Rollup merge of rust-lang#107270 - cjgillot:remove-zst, r=oli-obk
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Replace ZST operands and debuginfo by constants.

This is work that ConstProp will not have to do.
Split from rust-lang#107267
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@matthiaskrgr
matthiaskrgr authored Jan 26, 2023
2 parents ca7a610 + 49f4399 commit 71fa6ef
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Showing 29 changed files with 304 additions and 183 deletions.
132 changes: 103 additions & 29 deletions compiler/rustc_mir_transform/src/remove_zsts.rs
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Original file line number Diff line number Diff line change
@@ -1,7 +1,9 @@
//! Removes assignments to ZST places.
//! Removes operations on ZST places, and convert ZST operands to constants.

use crate::MirPass;
use rustc_middle::mir::{Body, StatementKind};
use rustc_middle::mir::interpret::ConstValue;
use rustc_middle::mir::visit::*;
use rustc_middle::mir::*;
use rustc_middle::ty::{self, Ty, TyCtxt};

pub struct RemoveZsts;
Expand All @@ -16,38 +18,24 @@ impl<'tcx> MirPass<'tcx> for RemoveZsts {
if tcx.type_of(body.source.def_id()).is_generator() {
return;
}
let param_env = tcx.param_env(body.source.def_id());
let basic_blocks = body.basic_blocks.as_mut_preserves_cfg();
let param_env = tcx.param_env_reveal_all_normalized(body.source.def_id());
let local_decls = &body.local_decls;
for block in basic_blocks {
for statement in block.statements.iter_mut() {
if let StatementKind::Assign(box (place, _)) | StatementKind::Deinit(box place) =
statement.kind
{
let place_ty = place.ty(local_decls, tcx).ty;
if !maybe_zst(place_ty) {
continue;
}
let Ok(layout) = tcx.layout_of(param_env.and(place_ty)) else {
continue;
};
if !layout.is_zst() {
continue;
}
if tcx.consider_optimizing(|| {
format!(
"RemoveZsts - Place: {:?} SourceInfo: {:?}",
place, statement.source_info
)
}) {
statement.make_nop();
}
}
}
let mut replacer = Replacer { tcx, param_env, local_decls };
for var_debug_info in &mut body.var_debug_info {
replacer.visit_var_debug_info(var_debug_info);
}
for (bb, data) in body.basic_blocks.as_mut_preserves_cfg().iter_enumerated_mut() {
replacer.visit_basic_block_data(bb, data);
}
}
}

struct Replacer<'a, 'tcx> {
tcx: TyCtxt<'tcx>,
param_env: ty::ParamEnv<'tcx>,
local_decls: &'a LocalDecls<'tcx>,
}

/// A cheap, approximate check to avoid unnecessary `layout_of` calls.
fn maybe_zst(ty: Ty<'_>) -> bool {
match ty.kind() {
Expand All @@ -63,3 +51,89 @@ fn maybe_zst(ty: Ty<'_>) -> bool {
_ => false,
}
}

impl<'tcx> Replacer<'_, 'tcx> {
fn known_to_be_zst(&self, ty: Ty<'tcx>) -> bool {
if !maybe_zst(ty) {
return false;
}
let Ok(layout) = self.tcx.layout_of(self.param_env.and(ty)) else {
return false;
};
layout.is_zst()
}

fn make_zst(&self, ty: Ty<'tcx>) -> Constant<'tcx> {
debug_assert!(self.known_to_be_zst(ty));
Constant {
span: rustc_span::DUMMY_SP,
user_ty: None,
literal: ConstantKind::Val(ConstValue::ZeroSized, ty),
}
}
}

impl<'tcx> MutVisitor<'tcx> for Replacer<'_, 'tcx> {
fn tcx(&self) -> TyCtxt<'tcx> {
self.tcx
}

fn visit_var_debug_info(&mut self, var_debug_info: &mut VarDebugInfo<'tcx>) {
match var_debug_info.value {
VarDebugInfoContents::Const(_) => {}
VarDebugInfoContents::Place(place) => {
let place_ty = place.ty(self.local_decls, self.tcx).ty;
if self.known_to_be_zst(place_ty) {
var_debug_info.value = VarDebugInfoContents::Const(self.make_zst(place_ty))
}
}
VarDebugInfoContents::Composite { ty, fragments: _ } => {
if self.known_to_be_zst(ty) {
var_debug_info.value = VarDebugInfoContents::Const(self.make_zst(ty))
}
}
}
}

fn visit_operand(&mut self, operand: &mut Operand<'tcx>, loc: Location) {
if let Operand::Constant(_) = operand {
return;
}
let op_ty = operand.ty(self.local_decls, self.tcx);
if self.known_to_be_zst(op_ty)
&& self.tcx.consider_optimizing(|| {
format!("RemoveZsts - Operand: {:?} Location: {:?}", operand, loc)
})
{
*operand = Operand::Constant(Box::new(self.make_zst(op_ty)))
}
}

fn visit_statement(&mut self, statement: &mut Statement<'tcx>, loc: Location) {
let place_for_ty = match statement.kind {
StatementKind::Assign(box (place, ref rvalue)) => {
rvalue.is_safe_to_remove().then_some(place)
}
StatementKind::Deinit(box place)
| StatementKind::SetDiscriminant { box place, variant_index: _ }
| StatementKind::AscribeUserType(box (place, _), _)
| StatementKind::Retag(_, box place)
| StatementKind::FakeRead(box (_, place)) => Some(place),
StatementKind::StorageLive(local) | StatementKind::StorageDead(local) => {
Some(local.into())
}
StatementKind::Coverage(_) | StatementKind::Intrinsic(_) | StatementKind::Nop => None,
};
if let Some(place_for_ty) = place_for_ty
&& let ty = place_for_ty.ty(self.local_decls, self.tcx).ty
&& self.known_to_be_zst(ty)
&& self.tcx.consider_optimizing(|| {
format!("RemoveZsts - Place: {:?} SourceInfo: {:?}", place_for_ty, statement.source_info)
})
{
statement.make_nop();
} else {
self.super_statement(statement, loc);
}
}
}
1 change: 0 additions & 1 deletion tests/mir-opt/const_prop/control_flow_simplification.hello.ConstProp.diff
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Original file line number Diff line number Diff line change
Expand Up @@ -14,7 +14,6 @@
}

bb1: {
StorageLive(_2); // scope 0 at $SRC_DIR/std/src/panic.rs:LL:COL
_2 = begin_panic::<&str>(const "explicit panic"); // scope 0 at $SRC_DIR/std/src/panic.rs:LL:COL
// mir::Constant
// + span: $SRC_DIR/std/src/panic.rs:LL:COL
Expand Down
14 changes: 4 additions & 10 deletions tests/mir-opt/const_prop/invalid_constant.main.ConstProp.diff
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Original file line number Diff line number Diff line change
Expand Up @@ -12,12 +12,10 @@
let _3: [E; 1]; // in scope 1 at $DIR/invalid_constant.rs:+13:9: +13:21
scope 3 {
debug _invalid_tag => _3; // in scope 3 at $DIR/invalid_constant.rs:+13:9: +13:21
let _6: [Empty; 1]; // in scope 3 at $DIR/invalid_constant.rs:+20:9: +20:31
scope 5 {
debug _enum_without_variants => _6; // in scope 5 at $DIR/invalid_constant.rs:+20:9: +20:31
let _7: main::Str<"���">; // in scope 5 at $DIR/invalid_constant.rs:+24:9: +24:22
debug _enum_without_variants => const [ZeroSized: Empty]; // in scope 5 at $DIR/invalid_constant.rs:+20:9: +20:31
scope 7 {
debug _non_utf8_str => _7; // in scope 7 at $DIR/invalid_constant.rs:+24:9: +24:22
debug _non_utf8_str => const Str::<"���">; // in scope 7 at $DIR/invalid_constant.rs:+24:9: +24:22
}
}
scope 6 {
Expand Down Expand Up @@ -46,18 +44,14 @@
- _3 = [move _4]; // scope 1 at $DIR/invalid_constant.rs:+13:24: +13:60
+ _4 = const Scalar(0x00000004): E; // scope 4 at $DIR/invalid_constant.rs:+13:34: +13:57
+ // mir::Constant
+ // + span: $DIR/invalid_constant.rs:28:34: 28:57
+ // + span: $DIR/invalid_constant.rs:29:34: 29:57
+ // + literal: Const { ty: E, val: Value(Scalar(0x00000004)) }
+ _3 = [const Scalar(0x00000004): E]; // scope 1 at $DIR/invalid_constant.rs:+13:24: +13:60
+ // mir::Constant
+ // + span: $DIR/invalid_constant.rs:28:24: 28:60
+ // + span: $DIR/invalid_constant.rs:29:24: 29:60
+ // + literal: Const { ty: E, val: Value(Scalar(0x00000004)) }
StorageDead(_4); // scope 1 at $DIR/invalid_constant.rs:+13:59: +13:60
StorageDead(_5); // scope 1 at $DIR/invalid_constant.rs:+13:60: +13:61
StorageLive(_6); // scope 3 at $DIR/invalid_constant.rs:+20:9: +20:31
StorageLive(_7); // scope 5 at $DIR/invalid_constant.rs:+24:9: +24:22
StorageDead(_7); // scope 5 at $DIR/invalid_constant.rs:+27:1: +27:2
StorageDead(_6); // scope 3 at $DIR/invalid_constant.rs:+27:1: +27:2
StorageDead(_3); // scope 1 at $DIR/invalid_constant.rs:+27:1: +27:2
StorageDead(_1); // scope 0 at $DIR/invalid_constant.rs:+27:1: +27:2
return; // scope 0 at $DIR/invalid_constant.rs:+27:2: +27:2
Expand Down
79 changes: 79 additions & 0 deletions tests/mir-opt/const_prop/invalid_constant.main.RemoveZsts.diff
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Original file line number Diff line number Diff line change
@@ -0,0 +1,79 @@
- // MIR for `main` before RemoveZsts
+ // MIR for `main` after RemoveZsts

fn main() -> () {
let mut _0: (); // return place in scope 0 at $DIR/invalid_constant.rs:+0:11: +0:11
let _1: char; // in scope 0 at $DIR/invalid_constant.rs:+6:9: +6:22
let mut _2: main::InvalidChar; // in scope 0 at $DIR/invalid_constant.rs:+6:34: +6:63
let mut _4: E; // in scope 0 at $DIR/invalid_constant.rs:+13:25: +13:59
let mut _5: main::InvalidTag; // in scope 0 at $DIR/invalid_constant.rs:+13:34: +13:55
let mut _7: Empty; // in scope 0 at $DIR/invalid_constant.rs:+20:35: +20:73
let mut _8: main::NoVariants; // in scope 0 at $DIR/invalid_constant.rs:+20:44: +20:65
scope 1 {
debug _invalid_char => _1; // in scope 1 at $DIR/invalid_constant.rs:+6:9: +6:22
let _3: [E; 1]; // in scope 1 at $DIR/invalid_constant.rs:+13:9: +13:21
scope 3 {
debug _invalid_tag => _3; // in scope 3 at $DIR/invalid_constant.rs:+13:9: +13:21
let _6: [Empty; 1]; // in scope 3 at $DIR/invalid_constant.rs:+20:9: +20:31
scope 5 {
- debug _enum_without_variants => _6; // in scope 5 at $DIR/invalid_constant.rs:+20:9: +20:31
+ debug _enum_without_variants => const [ZeroSized: Empty]; // in scope 5 at $DIR/invalid_constant.rs:+20:9: +20:31
let _9: main::Str<"���">; // in scope 5 at $DIR/invalid_constant.rs:+24:9: +24:22
scope 7 {
- debug _non_utf8_str => _9; // in scope 7 at $DIR/invalid_constant.rs:+24:9: +24:22
+ debug _non_utf8_str => const Str::<"���">; // in scope 7 at $DIR/invalid_constant.rs:+24:9: +24:22
}
}
scope 6 {
}
}
scope 4 {
}
}
scope 2 {
}

bb0: {
StorageLive(_1); // scope 0 at $DIR/invalid_constant.rs:+6:9: +6:22
StorageLive(_2); // scope 2 at $DIR/invalid_constant.rs:+6:34: +6:63
Deinit(_2); // scope 2 at $DIR/invalid_constant.rs:+6:34: +6:63
(_2.0: u32) = const 1114113_u32; // scope 2 at $DIR/invalid_constant.rs:+6:34: +6:63
_1 = (_2.1: char); // scope 2 at $DIR/invalid_constant.rs:+6:34: +6:67
StorageDead(_2); // scope 0 at $DIR/invalid_constant.rs:+6:69: +6:70
StorageLive(_3); // scope 1 at $DIR/invalid_constant.rs:+13:9: +13:21
StorageLive(_4); // scope 1 at $DIR/invalid_constant.rs:+13:25: +13:59
StorageLive(_5); // scope 4 at $DIR/invalid_constant.rs:+13:34: +13:55
Deinit(_5); // scope 4 at $DIR/invalid_constant.rs:+13:34: +13:55
(_5.0: u32) = const 4_u32; // scope 4 at $DIR/invalid_constant.rs:+13:34: +13:55
_4 = (_5.1: E); // scope 4 at $DIR/invalid_constant.rs:+13:34: +13:57
_3 = [move _4]; // scope 1 at $DIR/invalid_constant.rs:+13:24: +13:60
StorageDead(_4); // scope 1 at $DIR/invalid_constant.rs:+13:59: +13:60
StorageDead(_5); // scope 1 at $DIR/invalid_constant.rs:+13:60: +13:61
- StorageLive(_6); // scope 3 at $DIR/invalid_constant.rs:+20:9: +20:31
- StorageLive(_7); // scope 3 at $DIR/invalid_constant.rs:+20:35: +20:73
+ nop; // scope 3 at $DIR/invalid_constant.rs:+20:9: +20:31
+ nop; // scope 3 at $DIR/invalid_constant.rs:+20:35: +20:73
StorageLive(_8); // scope 6 at $DIR/invalid_constant.rs:+20:44: +20:65
Deinit(_8); // scope 6 at $DIR/invalid_constant.rs:+20:44: +20:65
(_8.0: u32) = const 0_u32; // scope 6 at $DIR/invalid_constant.rs:+20:44: +20:65
- _7 = (_8.1: Empty); // scope 6 at $DIR/invalid_constant.rs:+20:44: +20:71
- _6 = [move _7]; // scope 3 at $DIR/invalid_constant.rs:+20:34: +20:74
- StorageDead(_7); // scope 3 at $DIR/invalid_constant.rs:+20:73: +20:74
+ nop; // scope 6 at $DIR/invalid_constant.rs:+20:44: +20:71
+ nop; // scope 3 at $DIR/invalid_constant.rs:+20:34: +20:74
+ nop; // scope 3 at $DIR/invalid_constant.rs:+20:73: +20:74
StorageDead(_8); // scope 3 at $DIR/invalid_constant.rs:+20:74: +20:75
- StorageLive(_9); // scope 5 at $DIR/invalid_constant.rs:+24:9: +24:22
- _0 = const (); // scope 0 at $DIR/invalid_constant.rs:+0:11: +27:2
- StorageDead(_9); // scope 5 at $DIR/invalid_constant.rs:+27:1: +27:2
- StorageDead(_6); // scope 3 at $DIR/invalid_constant.rs:+27:1: +27:2
+ nop; // scope 5 at $DIR/invalid_constant.rs:+24:9: +24:22
+ nop; // scope 0 at $DIR/invalid_constant.rs:+0:11: +27:2
+ nop; // scope 5 at $DIR/invalid_constant.rs:+27:1: +27:2
+ nop; // scope 3 at $DIR/invalid_constant.rs:+27:1: +27:2
StorageDead(_3); // scope 1 at $DIR/invalid_constant.rs:+27:1: +27:2
StorageDead(_1); // scope 0 at $DIR/invalid_constant.rs:+27:1: +27:2
return; // scope 0 at $DIR/invalid_constant.rs:+27:2: +27:2
}
}

1 change: 1 addition & 0 deletions tests/mir-opt/const_prop/invalid_constant.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -11,6 +11,7 @@ enum E { A, B, C }
#[derive(Copy, Clone)]
enum Empty {}

// EMIT_MIR invalid_constant.main.RemoveZsts.diff
// EMIT_MIR invalid_constant.main.ConstProp.diff
fn main() {
// An invalid char.
Expand Down
2 changes: 0 additions & 2 deletions tests/mir-opt/const_prop/issue_66971.main.ConstProp.diff
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Original file line number Diff line number Diff line change
Expand Up @@ -7,7 +7,6 @@
let mut _2: ((), u8, u8); // in scope 0 at $DIR/issue_66971.rs:+1:12: +1:22

bb0: {
StorageLive(_1); // scope 0 at $DIR/issue_66971.rs:+1:5: +1:23
StorageLive(_2); // scope 0 at $DIR/issue_66971.rs:+1:12: +1:22
Deinit(_2); // scope 0 at $DIR/issue_66971.rs:+1:12: +1:22
(_2.1: u8) = const 0_u8; // scope 0 at $DIR/issue_66971.rs:+1:12: +1:22
Expand All @@ -20,7 +19,6 @@

bb1: {
StorageDead(_2); // scope 0 at $DIR/issue_66971.rs:+1:22: +1:23
StorageDead(_1); // scope 0 at $DIR/issue_66971.rs:+1:23: +1:24
return; // scope 0 at $DIR/issue_66971.rs:+2:2: +2:2
}
}
Expand Down
2 changes: 0 additions & 2 deletions tests/mir-opt/const_prop/issue_67019.main.ConstProp.diff
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Original file line number Diff line number Diff line change
Expand Up @@ -8,7 +8,6 @@
let mut _3: (u8, u8); // in scope 0 at $DIR/issue_67019.rs:+1:11: +1:17

bb0: {
StorageLive(_1); // scope 0 at $DIR/issue_67019.rs:+1:5: +1:20
StorageLive(_2); // scope 0 at $DIR/issue_67019.rs:+1:10: +1:19
StorageLive(_3); // scope 0 at $DIR/issue_67019.rs:+1:11: +1:17
Deinit(_3); // scope 0 at $DIR/issue_67019.rs:+1:11: +1:17
Expand All @@ -26,7 +25,6 @@

bb1: {
StorageDead(_2); // scope 0 at $DIR/issue_67019.rs:+1:19: +1:20
StorageDead(_1); // scope 0 at $DIR/issue_67019.rs:+1:20: +1:21
return; // scope 0 at $DIR/issue_67019.rs:+2:2: +2:2
}
}
Expand Down
2 changes: 0 additions & 2 deletions tests/mir-opt/const_prop/scalar_literal_propagation.main.ConstProp.diff
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Original file line number Diff line number Diff line change
Expand Up @@ -13,7 +13,6 @@
bb0: {
StorageLive(_1); // scope 0 at $DIR/scalar_literal_propagation.rs:+1:9: +1:10
_1 = const 1_u32; // scope 0 at $DIR/scalar_literal_propagation.rs:+1:13: +1:14
StorageLive(_2); // scope 1 at $DIR/scalar_literal_propagation.rs:+2:5: +2:15
StorageLive(_3); // scope 1 at $DIR/scalar_literal_propagation.rs:+2:13: +2:14
- _3 = _1; // scope 1 at $DIR/scalar_literal_propagation.rs:+2:13: +2:14
- _2 = consume(move _3) -> bb1; // scope 1 at $DIR/scalar_literal_propagation.rs:+2:5: +2:15
Expand All @@ -26,7 +25,6 @@

bb1: {
StorageDead(_3); // scope 1 at $DIR/scalar_literal_propagation.rs:+2:14: +2:15
StorageDead(_2); // scope 1 at $DIR/scalar_literal_propagation.rs:+2:15: +2:16
StorageDead(_1); // scope 0 at $DIR/scalar_literal_propagation.rs:+3:1: +3:2
return; // scope 0 at $DIR/scalar_literal_propagation.rs:+3:2: +3:2
}
Expand Down
2 changes: 0 additions & 2 deletions tests/mir-opt/const_prop/tuple_literal_propagation.main.ConstProp.diff
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Original file line number Diff line number Diff line change
Expand Up @@ -15,7 +15,6 @@
Deinit(_1); // scope 0 at $DIR/tuple_literal_propagation.rs:+1:13: +1:19
(_1.0: u32) = const 1_u32; // scope 0 at $DIR/tuple_literal_propagation.rs:+1:13: +1:19
(_1.1: u32) = const 2_u32; // scope 0 at $DIR/tuple_literal_propagation.rs:+1:13: +1:19
StorageLive(_2); // scope 1 at $DIR/tuple_literal_propagation.rs:+3:5: +3:15
StorageLive(_3); // scope 1 at $DIR/tuple_literal_propagation.rs:+3:13: +3:14
- _3 = _1; // scope 1 at $DIR/tuple_literal_propagation.rs:+3:13: +3:14
+ _3 = const (1_u32, 2_u32); // scope 1 at $DIR/tuple_literal_propagation.rs:+3:13: +3:14
Expand All @@ -27,7 +26,6 @@

bb1: {
StorageDead(_3); // scope 1 at $DIR/tuple_literal_propagation.rs:+3:14: +3:15
StorageDead(_2); // scope 1 at $DIR/tuple_literal_propagation.rs:+3:15: +3:16
StorageDead(_1); // scope 0 at $DIR/tuple_literal_propagation.rs:+4:1: +4:2
return; // scope 0 at $DIR/tuple_literal_propagation.rs:+4:2: +4:2
}
Expand Down
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