diff --git a/compiler/rustc_mir_transform/src/ref_prop.rs b/compiler/rustc_mir_transform/src/ref_prop.rs index dafd2ae23a63..ac55ce3b3168 100644 --- a/compiler/rustc_mir_transform/src/ref_prop.rs +++ b/compiler/rustc_mir_transform/src/ref_prop.rs @@ -85,7 +85,9 @@ fn propagate_ssa<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) { let ssa = SsaLocals::new(body); let mut replacer = compute_replacement(tcx, body, &ssa); - debug!(?replacer.targets, ?replacer.allowed_replacements, ?replacer.storage_to_remove); + debug!(?replacer.targets); + debug!(?replacer.allowed_replacements); + debug!(?replacer.storage_to_remove); replacer.visit_body_preserves_cfg(body); @@ -190,8 +192,11 @@ fn compute_replacement<'tcx>( continue; } + // Whether the current local is subject to the uniqueness rule. + let needs_unique = ty.is_mutable_ptr(); + // If this a mutable reference that we cannot fully replace, mark it as unknown. - if ty.is_mutable_ptr() && !fully_replacable_locals.contains(local) { + if needs_unique && !fully_replacable_locals.contains(local) { debug!("not fully replaceable"); continue; } @@ -217,10 +222,10 @@ fn compute_replacement<'tcx>( let mut place = *place; // Try to see through `place` in order to collapse reborrow chains. if place.projection.first() == Some(&PlaceElem::Deref) - && let Value::Pointer(target, refmut) = targets[place.local] + && let Value::Pointer(target, needs_unique) = targets[place.local] // Only see through immutable reference and pointers, as we do not know yet if // mutable references are fully replaced. - && !refmut + && !needs_unique // Only collapse chain if the pointee is definitely live. && can_perform_opt(target, location) { @@ -228,7 +233,7 @@ fn compute_replacement<'tcx>( } assert_ne!(place.local, local); if is_constant_place(place) { - targets[local] = Value::Pointer(place, ty.is_mutable_ptr()); + targets[local] = Value::Pointer(place, needs_unique); } } // We do not know what to do, so keep as not-a-pointer. @@ -276,16 +281,35 @@ fn compute_replacement<'tcx>( return; } - if let Value::Pointer(target, refmut) = self.targets[place.local] - && place.projection.first() == Some(&PlaceElem::Deref) - { - let perform_opt = (self.can_perform_opt)(target, loc); - if perform_opt { - self.allowed_replacements.insert((target.local, loc)); - } else if refmut { - // This mutable reference is not fully replacable, so drop it. - self.targets[place.local] = Value::Unknown; + if place.projection.first() != Some(&PlaceElem::Deref) { + // This is not a dereference, nothing to do. + return; + } + + let mut place = place.as_ref(); + loop { + if let Value::Pointer(target, needs_unique) = self.targets[place.local] { + let perform_opt = (self.can_perform_opt)(target, loc); + debug!(?place, ?target, ?needs_unique, ?perform_opt); + + // This a reborrow chain, recursively allow the replacement. + // + // This also allows to detect cases where `target.local` is not replacable, + // and mark it as such. + if let &[PlaceElem::Deref] = &target.projection[..] { + assert!(perform_opt); + self.allowed_replacements.insert((target.local, loc)); + place.local = target.local; + continue; + } else if perform_opt { + self.allowed_replacements.insert((target.local, loc)); + } else if needs_unique { + // This mutable reference is not fully replacable, so drop it. + self.targets[place.local] = Value::Unknown; + } } + + break; } } } @@ -326,18 +350,23 @@ impl<'tcx> MutVisitor<'tcx> for Replacer<'tcx> { } fn visit_place(&mut self, place: &mut Place<'tcx>, ctxt: PlaceContext, loc: Location) { - if let Value::Pointer(target, _) = self.targets[place.local] - && place.projection.first() == Some(&PlaceElem::Deref) - { - let perform_opt = matches!(ctxt, PlaceContext::NonUse(_)) - || self.allowed_replacements.contains(&(target.local, loc)); + if place.projection.first() != Some(&PlaceElem::Deref) { + return; + } - if perform_opt { - *place = target.project_deeper(&place.projection[1..], self.tcx); - self.any_replacement = true; + loop { + if let Value::Pointer(target, _) = self.targets[place.local] { + let perform_opt = matches!(ctxt, PlaceContext::NonUse(_)) + || self.allowed_replacements.contains(&(target.local, loc)); + + if perform_opt { + *place = target.project_deeper(&place.projection[1..], self.tcx); + self.any_replacement = true; + continue; + } } - } else { - self.super_place(place, ctxt, loc); + + break; } } diff --git a/tests/mir-opt/reference_prop.mut_raw_then_mut_shr.ReferencePropagation.diff b/tests/mir-opt/reference_prop.mut_raw_then_mut_shr.ReferencePropagation.diff index c137705a39a9..ed9f8c2b1876 100644 --- a/tests/mir-opt/reference_prop.mut_raw_then_mut_shr.ReferencePropagation.diff +++ b/tests/mir-opt/reference_prop.mut_raw_then_mut_shr.ReferencePropagation.diff @@ -41,8 +41,7 @@ - StorageLive(_5); // scope 2 at $DIR/reference_prop.rs:+3:16: +3:26 - _5 = &mut (*_2); // scope 2 at $DIR/reference_prop.rs:+3:16: +3:26 - _4 = &raw mut (*_5); // scope 2 at $DIR/reference_prop.rs:+3:16: +3:26 -+ _5 = &mut _1; // scope 2 at $DIR/reference_prop.rs:+3:16: +3:26 -+ _4 = &raw mut (*_2); // scope 2 at $DIR/reference_prop.rs:+3:16: +3:26 ++ _4 = &raw mut _1; // scope 2 at $DIR/reference_prop.rs:+3:16: +3:26 _3 = _4; // scope 2 at $DIR/reference_prop.rs:+3:16: +3:36 - StorageDead(_5); // scope 2 at $DIR/reference_prop.rs:+3:36: +3:37 StorageDead(_4); // scope 2 at $DIR/reference_prop.rs:+3:36: +3:37 @@ -55,8 +54,8 @@ - (*_3) = const 4_i32; // scope 6 at $DIR/reference_prop.rs:+7:14: +7:23 - _8 = const (); // scope 6 at $DIR/reference_prop.rs:+7:5: +7:26 - StorageDead(_8); // scope 5 at $DIR/reference_prop.rs:+7:25: +7:26 -+ _7 = (*_2); // scope 4 at $DIR/reference_prop.rs:+6:13: +6:18 -+ (*_5) = const 4_i32; // scope 6 at $DIR/reference_prop.rs:+7:14: +7:23 ++ _7 = _1; // scope 4 at $DIR/reference_prop.rs:+6:13: +6:18 ++ _1 = const 4_i32; // scope 6 at $DIR/reference_prop.rs:+7:14: +7:23 StorageLive(_9); // scope 5 at $DIR/reference_prop.rs:+8:6: +8:7 _9 = _7; // scope 5 at $DIR/reference_prop.rs:+8:6: +8:7 StorageLive(_10); // scope 5 at $DIR/reference_prop.rs:+8:9: +8:10 diff --git a/tests/mir-opt/reference_prop.read_through_raw.ReferencePropagation.diff b/tests/mir-opt/reference_prop.read_through_raw.ReferencePropagation.diff index a7d505c69066..75c1f8f57cca 100644 --- a/tests/mir-opt/reference_prop.read_through_raw.ReferencePropagation.diff +++ b/tests/mir-opt/reference_prop.read_through_raw.ReferencePropagation.diff @@ -9,15 +9,14 @@ let mut _5: *mut usize; // in scope 0 at $SRC_DIR/core/src/intrinsics/mir.rs:LL:COL bb0: { - _2 = &mut (*_1); // scope 0 at $DIR/reference_prop.rs:+10:13: +10:25 +- _2 = &mut (*_1); // scope 0 at $DIR/reference_prop.rs:+10:13: +10:25 - _3 = &mut (*_2); // scope 0 at $DIR/reference_prop.rs:+11:13: +11:26 - _4 = &raw mut (*_2); // scope 0 at $DIR/reference_prop.rs:+12:13: +12:30 - _5 = &raw mut (*_3); // scope 0 at $DIR/reference_prop.rs:+13:13: +13:30 - _0 = (*_4); // scope 0 at $DIR/reference_prop.rs:+15:13: +15:22 - _0 = (*_5); // scope 0 at $DIR/reference_prop.rs:+16:13: +16:22 -+ _3 = &mut (*_1); // scope 0 at $DIR/reference_prop.rs:+11:13: +11:26 -+ _0 = (*_2); // scope 0 at $DIR/reference_prop.rs:+15:13: +15:22 -+ _0 = (*_3); // scope 0 at $DIR/reference_prop.rs:+16:13: +16:22 ++ _0 = (*_1); // scope 0 at $DIR/reference_prop.rs:+15:13: +15:22 ++ _0 = (*_1); // scope 0 at $DIR/reference_prop.rs:+16:13: +16:22 return; // scope 0 at $DIR/reference_prop.rs:+17:13: +17:21 } }