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Auto merge of #110824 - cjgillot:const-prop-index, r=JakobDegen,oli-obk 

ConstProp into PlaceElem::Index.

Noticed this while looking at keccak output MIR.

This pass aims to replace `ProjectionElem::Index` with `ProjectionElem::ConstantIndex` during ConstProp.

r? `@ghost`
This commit is contained in:
bors 2023-05-08 14:23:13 +00:00
parent ce042889f7 a8988519d5
commit a0111af531
5 changed files with 26 additions and 4 deletions
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18
compiler/rustc_mir_transform/src/const_prop.rs
View File

@ -806,6 +806,24 @@ impl<'tcx> MutVisitor<'tcx> for ConstPropagator<'_, 'tcx> {
}
}
fn process_projection_elem(
&mut self,
elem: PlaceElem<'tcx>,
_: Location,
) -> Option<PlaceElem<'tcx>> {
if let PlaceElem::Index(local) = elem
&& let Some(value) = self.get_const(local.into())
&& self.should_const_prop(&value)
&& let interpret::Operand::Immediate(interpret::Immediate::Scalar(scalar)) = *value
&& let Ok(offset) = scalar.to_target_usize(&self.tcx)
&& let Some(min_length) = offset.checked_add(1)
{
Some(PlaceElem::ConstantIndex { offset, min_length, from_end: false })
} else {
None
}
}
fn visit_assign(
&mut self,
place: &mut Place<'tcx>,

3
tests/mir-opt/const_prop/bad_op_unsafe_oob_for_slices.main.ConstProp.32bit.diff
View File

@ -45,7 +45,8 @@
}
bb1: {
_5 = (*_1)[_6]; // scope 2 at $DIR/bad_op_unsafe_oob_for_slices.rs:+3:18: +3:25
- _5 = (*_1)[_6]; // scope 2 at $DIR/bad_op_unsafe_oob_for_slices.rs:+3:18: +3:25
+ _5 = (*_1)[3 of 4]; // scope 2 at $DIR/bad_op_unsafe_oob_for_slices.rs:+3:18: +3:25
StorageDead(_6); // scope 2 at $DIR/bad_op_unsafe_oob_for_slices.rs:+3:25: +3:26
_0 = const (); // scope 2 at $DIR/bad_op_unsafe_oob_for_slices.rs:+2:5: +4:6
StorageDead(_5); // scope 2 at $DIR/bad_op_unsafe_oob_for_slices.rs:+4:5: +4:6

3
tests/mir-opt/const_prop/bad_op_unsafe_oob_for_slices.main.ConstProp.64bit.diff
View File

@ -45,7 +45,8 @@
}
bb1: {
_5 = (*_1)[_6]; // scope 2 at $DIR/bad_op_unsafe_oob_for_slices.rs:+3:18: +3:25
- _5 = (*_1)[_6]; // scope 2 at $DIR/bad_op_unsafe_oob_for_slices.rs:+3:18: +3:25
+ _5 = (*_1)[3 of 4]; // scope 2 at $DIR/bad_op_unsafe_oob_for_slices.rs:+3:18: +3:25
StorageDead(_6); // scope 2 at $DIR/bad_op_unsafe_oob_for_slices.rs:+3:25: +3:26
_0 = const (); // scope 2 at $DIR/bad_op_unsafe_oob_for_slices.rs:+2:5: +4:6
StorageDead(_5); // scope 2 at $DIR/bad_op_unsafe_oob_for_slices.rs:+4:5: +4:6

3
tests/mir-opt/const_prop/large_array_index.main.ConstProp.32bit.diff
View File

@ -27,7 +27,8 @@
}
bb1: {
_1 = _2[_3]; // scope 0 at $DIR/large_array_index.rs:+2:17: +2:32
- _1 = _2[_3]; // scope 0 at $DIR/large_array_index.rs:+2:17: +2:32
+ _1 = _2[2 of 3]; // scope 0 at $DIR/large_array_index.rs:+2:17: +2:32
StorageDead(_3); // scope 0 at $DIR/large_array_index.rs:+2:32: +2:33
StorageDead(_2); // scope 0 at $DIR/large_array_index.rs:+2:32: +2:33
_0 = const (); // scope 0 at $DIR/large_array_index.rs:+0:11: +3:2

3
tests/mir-opt/const_prop/large_array_index.main.ConstProp.64bit.diff
View File

@ -27,7 +27,8 @@
}
bb1: {
_1 = _2[_3]; // scope 0 at $DIR/large_array_index.rs:+2:17: +2:32
- _1 = _2[_3]; // scope 0 at $DIR/large_array_index.rs:+2:17: +2:32
+ _1 = _2[2 of 3]; // scope 0 at $DIR/large_array_index.rs:+2:17: +2:32
StorageDead(_3); // scope 0 at $DIR/large_array_index.rs:+2:32: +2:33
StorageDead(_2); // scope 0 at $DIR/large_array_index.rs:+2:32: +2:33
_0 = const (); // scope 0 at $DIR/large_array_index.rs:+0:11: +3:2