Skip to content

Avoid overflow in GVN constant indexing. #119052

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
merged 1 commit into from
Dec 17, 2023
Merged

Avoid overflow in GVN constant indexing. #119052

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
8 changes: 3 additions & 5 deletions compiler/rustc_mir_transform/src/gvn.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -644,12 +644,10 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
{
if let Some(offset) = self.evaluated[idx].as_ref()
&& let Ok(offset) = self.ecx.read_target_usize(offset)
&& let Some(min_length) = offset.checked_add(1)
{
projection.to_mut()[i] = ProjectionElem::ConstantIndex {
offset,
min_length: offset + 1,
from_end: false,
};
projection.to_mut()[i] =
ProjectionElem::ConstantIndex { offset, min_length, from_end: false };
Copy link
Member

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Do you know why ConstantIndex stores min_length instead of, e.g., the "max index" of the last value?

Copy link
Member

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Well I guess it doesn't make sense to index at usize::MAX anyways.

Copy link
Contributor Author

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

min_length comes from slice match. I supposed it's easier to compute from the length of the pattern.

} else if let Some(new_idx) = self.try_as_local(idx, location) {
projection.to_mut()[i] = ProjectionElem::Index(new_idx);
self.reused_locals.insert(new_idx);
Expand Down
104 changes: 104 additions & 0 deletions tests/mir-opt/gvn.constant_index_overflow.GVN.panic-abort.diff
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -0,0 +1,104 @@
- // MIR for `constant_index_overflow` before GVN
+ // MIR for `constant_index_overflow` after GVN

fn constant_index_overflow(_1: &[T]) -> () {
debug x => _1;
let mut _0: ();
let _2: usize;
let mut _4: bool;
let mut _5: usize;
let mut _6: usize;
let mut _7: &[T];
let _8: usize;
let mut _9: usize;
let mut _10: bool;
let _11: usize;
let mut _12: usize;
let mut _13: bool;
let mut _14: T;
scope 1 {
debug a => _2;
let _3: T;
scope 2 {
debug b => _3;
}
}

bb0: {
- StorageLive(_2);
- _2 = const _ as usize (IntToInt);
+ nop;
+ _2 = const usize::MAX;
StorageLive(_3);
StorageLive(_4);
StorageLive(_5);
- _5 = _2;
+ _5 = const usize::MAX;
StorageLive(_6);
StorageLive(_7);
_7 = &(*_1);
_6 = core::slice::<impl [T]>::len(move _7) -> [return: bb1, unwind unreachable];
}

bb1: {
StorageDead(_7);
- _4 = Lt(move _5, move _6);
+ _4 = Lt(const usize::MAX, move _6);
switchInt(move _4) -> [0: bb4, otherwise: bb2];
}

bb2: {
StorageDead(_6);
StorageDead(_5);
StorageLive(_8);
- _8 = _2;
+ _8 = const usize::MAX;
_9 = Len((*_1));
- _10 = Lt(_8, _9);
- assert(move _10, "index out of bounds: the length is {} but the index is {}", move _9, _8) -> [success: bb3, unwind unreachable];
+ _10 = Lt(const usize::MAX, _9);
+ assert(move _10, "index out of bounds: the length is {} but the index is {}", move _9, const usize::MAX) -> [success: bb3, unwind unreachable];
}

bb3: {
- _3 = (*_1)[_8];
+ _3 = (*_1)[_2];
StorageDead(_8);
goto -> bb6;
}

bb4: {
StorageDead(_6);
StorageDead(_5);
StorageLive(_11);
_11 = const 0_usize;
_12 = Len((*_1));
- _13 = Lt(_11, _12);
- assert(move _13, "index out of bounds: the length is {} but the index is {}", move _12, _11) -> [success: bb5, unwind unreachable];
+ _13 = Lt(const 0_usize, _12);
+ assert(move _13, "index out of bounds: the length is {} but the index is {}", move _12, const 0_usize) -> [success: bb5, unwind unreachable];
}

bb5: {
- _3 = (*_1)[_11];
+ _3 = (*_1)[0 of 1];
StorageDead(_11);
goto -> bb6;
}

bb6: {
StorageDead(_4);
StorageLive(_14);
_14 = _3;
_0 = opaque::<T>(move _14) -> [return: bb7, unwind unreachable];
}

bb7: {
StorageDead(_14);
StorageDead(_3);
- StorageDead(_2);
+ nop;
return;
}
}

104 changes: 104 additions & 0 deletions tests/mir-opt/gvn.constant_index_overflow.GVN.panic-unwind.diff
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -0,0 +1,104 @@
- // MIR for `constant_index_overflow` before GVN
+ // MIR for `constant_index_overflow` after GVN

fn constant_index_overflow(_1: &[T]) -> () {
debug x => _1;
let mut _0: ();
let _2: usize;
let mut _4: bool;
let mut _5: usize;
let mut _6: usize;
let mut _7: &[T];
let _8: usize;
let mut _9: usize;
let mut _10: bool;
let _11: usize;
let mut _12: usize;
let mut _13: bool;
let mut _14: T;
scope 1 {
debug a => _2;
let _3: T;
scope 2 {
debug b => _3;
}
}

bb0: {
- StorageLive(_2);
- _2 = const _ as usize (IntToInt);
+ nop;
+ _2 = const usize::MAX;
StorageLive(_3);
StorageLive(_4);
StorageLive(_5);
- _5 = _2;
+ _5 = const usize::MAX;
StorageLive(_6);
StorageLive(_7);
_7 = &(*_1);
_6 = core::slice::<impl [T]>::len(move _7) -> [return: bb1, unwind continue];
}

bb1: {
StorageDead(_7);
- _4 = Lt(move _5, move _6);
+ _4 = Lt(const usize::MAX, move _6);
switchInt(move _4) -> [0: bb4, otherwise: bb2];
}

bb2: {
StorageDead(_6);
StorageDead(_5);
StorageLive(_8);
- _8 = _2;
+ _8 = const usize::MAX;
_9 = Len((*_1));
- _10 = Lt(_8, _9);
- assert(move _10, "index out of bounds: the length is {} but the index is {}", move _9, _8) -> [success: bb3, unwind continue];
+ _10 = Lt(const usize::MAX, _9);
+ assert(move _10, "index out of bounds: the length is {} but the index is {}", move _9, const usize::MAX) -> [success: bb3, unwind continue];
}

bb3: {
- _3 = (*_1)[_8];
+ _3 = (*_1)[_2];
StorageDead(_8);
goto -> bb6;
}

bb4: {
StorageDead(_6);
StorageDead(_5);
StorageLive(_11);
_11 = const 0_usize;
_12 = Len((*_1));
- _13 = Lt(_11, _12);
- assert(move _13, "index out of bounds: the length is {} but the index is {}", move _12, _11) -> [success: bb5, unwind continue];
+ _13 = Lt(const 0_usize, _12);
+ assert(move _13, "index out of bounds: the length is {} but the index is {}", move _12, const 0_usize) -> [success: bb5, unwind continue];
}

bb5: {
- _3 = (*_1)[_11];
+ _3 = (*_1)[0 of 1];
StorageDead(_11);
goto -> bb6;
}

bb6: {
StorageDead(_4);
StorageLive(_14);
_14 = _3;
_0 = opaque::<T>(move _14) -> [return: bb7, unwind continue];
}

bb7: {
StorageDead(_14);
StorageDead(_3);
- StorageDead(_2);
+ nop;
return;
}
}

18 changes: 18 additions & 0 deletions tests/mir-opt/gvn.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -609,6 +609,22 @@ fn indirect_static() {
})
}

/// Verify that having constant index `u64::MAX` does not yield to an overflow in rustc.
fn constant_index_overflow<T: Copy>(x: &[T]) {
// CHECK-LABEL: fn constant_index_overflow(
// CHECK: debug a => [[a:_.*]];
// CHECK: debug b => [[b:_.*]];
// CHECK: [[a]] = const usize::MAX;
// CHECK-NOT: = (*_1)[{{.*}} of 0];
// CHECK: [[b]] = (*_1)[[[a]]];
// CHECK-NOT: = (*_1)[{{.*}} of 0];
// CHECK: [[b]] = (*_1)[0 of 1];
// CHECK-NOT: = (*_1)[{{.*}} of 0];
let a = u64::MAX as usize;
let b = if a < x.len() { x[a] } else { x[0] };
opaque(b)
}

fn main() {
subexpression_elimination(2, 4, 5);
wrap_unwrap(5);
Expand All @@ -627,6 +643,7 @@ fn main() {
repeat();
fn_pointers();
indirect_static();
constant_index_overflow(&[5, 3]);
}

#[inline(never)]
Expand All @@ -653,3 +670,4 @@ fn identity<T>(x: T) -> T {
// EMIT_MIR gvn.repeat.GVN.diff
// EMIT_MIR gvn.fn_pointers.GVN.diff
// EMIT_MIR gvn.indirect_static.GVN.diff
// EMIT_MIR gvn.constant_index_overflow.GVN.diff