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Special case deref projections in SsaVisitor.

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This commit is contained in:
Camille GILLOT 2023-02-17 17:36:43 +00:00
parent 43ee4d15bf
commit 2a32a2b64f
6 changed files with 222 additions and 14 deletions
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49
compiler/rustc_mir_transform/src/ssa.rs
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@ -179,6 +179,25 @@ struct SsaVisitor {
assignment_order: Vec<Local>,
}
impl SsaVisitor {
fn check_assignment_dominates(&mut self, local: Local, loc: Location) {
let set = &mut self.assignments[local];
let assign_dominates = match *set {
Set1::Empty | Set1::Many => false,
Set1::One(LocationExtended::Arg) => true,
Set1::One(LocationExtended::Plain(assign)) => {
assign.successor_within_block().dominates(loc, &self.dominators)
}
};
// We are visiting a use that is not dominated by an assignment.
// Either there is a cycle involved, or we are reading for uninitialized local.
// Bail out.
if !assign_dominates {
*set = Set1::Many;
}
}
}
impl<'tcx> Visitor<'tcx> for SsaVisitor {
fn visit_local(&mut self, local: Local, ctxt: PlaceContext, loc: Location) {
match ctxt {
@ -192,24 +211,26 @@ fn visit_local(&mut self, local: Local, ctxt: PlaceContext, loc: Location) {
// Immutable borrows are taken into account in `SsaLocals::new` by
// removing non-freeze locals.
PlaceContext::NonMutatingUse(_) => {
let set = &mut self.assignments[local];
let assign_dominates = match *set {
Set1::Empty | Set1::Many => false,
Set1::One(LocationExtended::Arg) => true,
Set1::One(LocationExtended::Plain(assign)) => {
assign.successor_within_block().dominates(loc, &self.dominators)
}
};
// We are visiting a use that is not dominated by an assignment.
// Either there is a cycle involved, or we are reading for uninitialized local.
// Bail out.
if !assign_dominates {
*set = Set1::Many;
}
self.check_assignment_dominates(local, loc);
}
PlaceContext::NonUse(_) => {}
}
}
fn visit_place(&mut self, place: &Place<'tcx>, ctxt: PlaceContext, loc: Location) {
if place.projection.first() == Some(&PlaceElem::Deref) {
// Do not do anything for storage statements and debuginfo.
if ctxt.is_use() {
// A use through a `deref` only reads from the local, and cannot write to it.
let new_ctxt = PlaceContext::NonMutatingUse(NonMutatingUseContext::Projection);
self.visit_projection(place.as_ref(), new_ctxt, loc);
self.check_assignment_dominates(place.local, loc);
}
return;
}
self.super_place(place, ctxt, loc);
}
}
#[instrument(level = "trace", skip(ssa, body))]

41
tests/mir-opt/copy-prop/reborrow.demiraw.CopyProp.diff Normal file
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@ -0,0 +1,41 @@
- // MIR for `demiraw` before CopyProp
+ // MIR for `demiraw` after CopyProp
fn demiraw(_1: u8) -> () {
debug x => _1; // in scope 0 at $DIR/reborrow.rs:+0:12: +0:17
let mut _0: (); // return place in scope 0 at $DIR/reborrow.rs:+0:23: +0:23
let _2: *mut u8; // in scope 0 at $DIR/reborrow.rs:+1:9: +1:10
let mut _4: &mut u8; // in scope 0 at $DIR/reborrow.rs:+2:22: +2:29
scope 1 {
debug a => _2; // in scope 1 at $DIR/reborrow.rs:+1:9: +1:10
let _3: &mut u8; // in scope 1 at $DIR/reborrow.rs:+2:9: +2:10
scope 2 {
debug b => _3; // in scope 2 at $DIR/reborrow.rs:+2:9: +2:10
let _5: *mut u8; // in scope 2 at $DIR/reborrow.rs:+3:9: +3:10
scope 4 {
- debug c => _5; // in scope 4 at $DIR/reborrow.rs:+3:9: +3:10
+ debug c => _2; // in scope 4 at $DIR/reborrow.rs:+3:9: +3:10
}
}
scope 3 {
}
}
bb0: {
- StorageLive(_2); // scope 0 at $DIR/reborrow.rs:+1:9: +1:10
_2 = &raw mut _1; // scope 0 at $DIR/reborrow.rs:+1:13: +1:23
StorageLive(_3); // scope 1 at $DIR/reborrow.rs:+2:9: +2:10
StorageLive(_4); // scope 1 at $DIR/reborrow.rs:+2:22: +2:29
_4 = &mut (*_2); // scope 3 at $DIR/reborrow.rs:+2:22: +2:29
_3 = &mut (*_4); // scope 1 at $DIR/reborrow.rs:+2:22: +2:29
StorageDead(_4); // scope 1 at $DIR/reborrow.rs:+2:31: +2:32
- StorageLive(_5); // scope 2 at $DIR/reborrow.rs:+3:9: +3:10
- _5 = _2; // scope 2 at $DIR/reborrow.rs:+3:13: +3:14
_0 = const (); // scope 0 at $DIR/reborrow.rs:+0:23: +4:2
- StorageDead(_5); // scope 2 at $DIR/reborrow.rs:+4:1: +4:2
StorageDead(_3); // scope 1 at $DIR/reborrow.rs:+4:1: +4:2
- StorageDead(_2); // scope 0 at $DIR/reborrow.rs:+4:1: +4:2
return; // scope 0 at $DIR/reborrow.rs:+4:2: +4:2
}
}

37
tests/mir-opt/copy-prop/reborrow.miraw.CopyProp.diff Normal file
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@ -0,0 +1,37 @@
- // MIR for `miraw` before CopyProp
+ // MIR for `miraw` after CopyProp
fn miraw(_1: u8) -> () {
debug x => _1; // in scope 0 at $DIR/reborrow.rs:+0:10: +0:15
let mut _0: (); // return place in scope 0 at $DIR/reborrow.rs:+0:21: +0:21
let _2: *mut u8; // in scope 0 at $DIR/reborrow.rs:+1:9: +1:10
scope 1 {
debug a => _2; // in scope 1 at $DIR/reborrow.rs:+1:9: +1:10
let _3: *mut u8; // in scope 1 at $DIR/reborrow.rs:+2:9: +2:10
scope 2 {
debug b => _3; // in scope 2 at $DIR/reborrow.rs:+2:9: +2:10
let _4: *mut u8; // in scope 2 at $DIR/reborrow.rs:+3:9: +3:10
scope 4 {
- debug c => _4; // in scope 4 at $DIR/reborrow.rs:+3:9: +3:10
+ debug c => _2; // in scope 4 at $DIR/reborrow.rs:+3:9: +3:10
}
}
scope 3 {
}
}
bb0: {
- StorageLive(_2); // scope 0 at $DIR/reborrow.rs:+1:9: +1:10
_2 = &raw mut _1; // scope 0 at $DIR/reborrow.rs:+1:13: +1:23
StorageLive(_3); // scope 1 at $DIR/reborrow.rs:+2:9: +2:10
_3 = &raw mut (*_2); // scope 3 at $DIR/reborrow.rs:+2:22: +2:33
- StorageLive(_4); // scope 2 at $DIR/reborrow.rs:+3:9: +3:10
- _4 = _2; // scope 2 at $DIR/reborrow.rs:+3:13: +3:14
_0 = const (); // scope 0 at $DIR/reborrow.rs:+0:21: +4:2
- StorageDead(_4); // scope 2 at $DIR/reborrow.rs:+4:1: +4:2
StorageDead(_3); // scope 1 at $DIR/reborrow.rs:+4:1: +4:2
- StorageDead(_2); // scope 0 at $DIR/reborrow.rs:+4:1: +4:2
return; // scope 0 at $DIR/reborrow.rs:+4:2: +4:2
}
}

35
tests/mir-opt/copy-prop/reborrow.remut.CopyProp.diff Normal file
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@ -0,0 +1,35 @@
- // MIR for `remut` before CopyProp
+ // MIR for `remut` after CopyProp
fn remut(_1: u8) -> () {
debug x => _1; // in scope 0 at $DIR/reborrow.rs:+0:10: +0:15
let mut _0: (); // return place in scope 0 at $DIR/reborrow.rs:+0:21: +0:21
let _2: &mut u8; // in scope 0 at $DIR/reborrow.rs:+1:9: +1:10
scope 1 {
debug a => _2; // in scope 1 at $DIR/reborrow.rs:+1:9: +1:10
let _3: &mut u8; // in scope 1 at $DIR/reborrow.rs:+2:9: +2:10
scope 2 {
debug b => _3; // in scope 2 at $DIR/reborrow.rs:+2:9: +2:10
let _4: &mut u8; // in scope 2 at $DIR/reborrow.rs:+3:9: +3:10
scope 3 {
- debug c => _4; // in scope 3 at $DIR/reborrow.rs:+3:9: +3:10
+ debug c => _2; // in scope 3 at $DIR/reborrow.rs:+3:9: +3:10
}
}
}
bb0: {
- StorageLive(_2); // scope 0 at $DIR/reborrow.rs:+1:9: +1:10
_2 = &mut _1; // scope 0 at $DIR/reborrow.rs:+1:13: +1:19
StorageLive(_3); // scope 1 at $DIR/reborrow.rs:+2:9: +2:10
_3 = &mut (*_2); // scope 1 at $DIR/reborrow.rs:+2:13: +2:20
- StorageLive(_4); // scope 2 at $DIR/reborrow.rs:+3:9: +3:10
- _4 = move _2; // scope 2 at $DIR/reborrow.rs:+3:13: +3:14
_0 = const (); // scope 0 at $DIR/reborrow.rs:+0:21: +4:2
- StorageDead(_4); // scope 2 at $DIR/reborrow.rs:+4:1: +4:2
StorageDead(_3); // scope 1 at $DIR/reborrow.rs:+4:1: +4:2
- StorageDead(_2); // scope 0 at $DIR/reborrow.rs:+4:1: +4:2
return; // scope 0 at $DIR/reborrow.rs:+4:2: +4:2
}
}

35
tests/mir-opt/copy-prop/reborrow.reraw.CopyProp.diff Normal file
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@ -0,0 +1,35 @@
- // MIR for `reraw` before CopyProp
+ // MIR for `reraw` after CopyProp
fn reraw(_1: u8) -> () {
debug x => _1; // in scope 0 at $DIR/reborrow.rs:+0:10: +0:15
let mut _0: (); // return place in scope 0 at $DIR/reborrow.rs:+0:21: +0:21
let _2: &mut u8; // in scope 0 at $DIR/reborrow.rs:+1:9: +1:10
scope 1 {
debug a => _2; // in scope 1 at $DIR/reborrow.rs:+1:9: +1:10
let _3: *mut u8; // in scope 1 at $DIR/reborrow.rs:+2:9: +2:10
scope 2 {
debug b => _3; // in scope 2 at $DIR/reborrow.rs:+2:9: +2:10
let _4: &mut u8; // in scope 2 at $DIR/reborrow.rs:+3:9: +3:10
scope 3 {
- debug c => _4; // in scope 3 at $DIR/reborrow.rs:+3:9: +3:10
+ debug c => _2; // in scope 3 at $DIR/reborrow.rs:+3:9: +3:10
}
}
}
bb0: {
- StorageLive(_2); // scope 0 at $DIR/reborrow.rs:+1:9: +1:10
_2 = &mut _1; // scope 0 at $DIR/reborrow.rs:+1:13: +1:19
StorageLive(_3); // scope 1 at $DIR/reborrow.rs:+2:9: +2:10
_3 = &raw mut (*_2); // scope 1 at $DIR/reborrow.rs:+2:13: +2:24
- StorageLive(_4); // scope 2 at $DIR/reborrow.rs:+3:9: +3:10
- _4 = move _2; // scope 2 at $DIR/reborrow.rs:+3:13: +3:14
_0 = const (); // scope 0 at $DIR/reborrow.rs:+0:21: +4:2
- StorageDead(_4); // scope 2 at $DIR/reborrow.rs:+4:1: +4:2
StorageDead(_3); // scope 1 at $DIR/reborrow.rs:+4:1: +4:2
- StorageDead(_2); // scope 0 at $DIR/reborrow.rs:+4:1: +4:2
return; // scope 0 at $DIR/reborrow.rs:+4:2: +4:2
}
}

39
tests/mir-opt/copy-prop/reborrow.rs Normal file
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@ -0,0 +1,39 @@
// Check that CopyProp considers reborrows as not mutating the pointer.
// unit-test: CopyProp
#![feature(raw_ref_op)]
// EMIT_MIR reborrow.remut.CopyProp.diff
fn remut(mut x: u8) {
let a = &mut x;
let b = &mut *a; //< this cannot mutate a.
let c = a; //< so `c` and `a` can be merged.
}
// EMIT_MIR reborrow.reraw.CopyProp.diff
fn reraw(mut x: u8) {
let a = &mut x;
let b = &raw mut *a; //< this cannot mutate a.
let c = a; //< so `c` and `a` can be merged.
}
// EMIT_MIR reborrow.miraw.CopyProp.diff
fn miraw(mut x: u8) {
let a = &raw mut x;
let b = unsafe { &raw mut *a }; //< this cannot mutate a.
let c = a; //< so `c` and `a` can be merged.
}
// EMIT_MIR reborrow.demiraw.CopyProp.diff
fn demiraw(mut x: u8) {
let a = &raw mut x;
let b = unsafe { &mut *a }; //< this cannot mutate a.
let c = a; //< so `c` and `a` can be merged.
}
fn main() {
remut(0);
reraw(0);
miraw(0);
demiraw(0);
}