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Don't reset cast kind without also updating the operand in simplify_cast in GVN #136450

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Merged
merged 2 commits into from
Feb 7, 2025
Merged

Don't reset cast kind without also updating the operand in simplify_cast in GVN #136450

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c215e80
Failing test
compiler-errors Feb 2, 2025
de7d4a8
Don't reset cast kind without also updating the operand in simplify_cast
compiler-errors Feb 2, 2025
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20 changes: 11 additions & 9 deletions compiler/rustc_mir_transform/src/gvn.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1367,16 +1367,17 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {

fn simplify_cast(
&mut self,
kind: &mut CastKind,
operand: &mut Operand<'tcx>,
initial_kind: &mut CastKind,
initial_operand: &mut Operand<'tcx>,
to: Ty<'tcx>,
location: Location,
) -> Option<VnIndex> {
use CastKind::*;
use rustc_middle::ty::adjustment::PointerCoercion::*;

let mut from = operand.ty(self.local_decls, self.tcx);
let mut value = self.simplify_operand(operand, location)?;
let mut from = initial_operand.ty(self.local_decls, self.tcx);
let mut kind = *initial_kind;
let mut value = self.simplify_operand(initial_operand, location)?;
if from == to {
return Some(value);
}
Expand All @@ -1400,7 +1401,7 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
&& to.is_unsafe_ptr()
&& self.pointers_have_same_metadata(from, to)
{
*kind = PtrToPtr;
kind = PtrToPtr;
was_updated_this_iteration = true;
}

Expand Down Expand Up @@ -1443,7 +1444,7 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
to: inner_to,
} = *self.get(value)
{
let new_kind = match (inner_kind, *kind) {
let new_kind = match (inner_kind, kind) {
// Even if there's a narrowing cast in here that's fine, because
// things like `*mut [i32] -> *mut i32 -> *const i32` and
// `*mut [i32] -> *const [i32] -> *const i32` can skip the middle in MIR.
Expand Down Expand Up @@ -1471,7 +1472,7 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
_ => None,
};
if let Some(new_kind) = new_kind {
*kind = new_kind;
kind = new_kind;
from = inner_from;
value = inner_value;
was_updated_this_iteration = true;
Expand All @@ -1489,10 +1490,11 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
}

if was_ever_updated && let Some(op) = self.try_as_operand(value, location) {
*operand = op;
*initial_operand = op;
*initial_kind = kind;
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Ah, moving these here is smart. Nice job!

Thanks for picking this up, compiler-errors.

}

Some(self.insert(Value::Cast { kind: *kind, value, from, to }))
Some(self.insert(Value::Cast { kind, value, from, to }))
}

fn simplify_len(&mut self, place: &mut Place<'tcx>, location: Location) -> Option<VnIndex> {
Expand Down
15 changes: 15 additions & 0 deletions tests/mir-opt/dont_reset_cast_kind_without_updating_operand.rs
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Original file line number Diff line number Diff line change
@@ -0,0 +1,15 @@
// skip-filecheck
//@ compile-flags: -Zmir-enable-passes=+Inline,+GVN --crate-type lib
// EMIT_MIR_FOR_EACH_PANIC_STRATEGY
// EMIT_MIR dont_reset_cast_kind_without_updating_operand.test.GVN.diff

fn test() {
let vp_ctx: &Box<()> = &Box::new(());
let slf: *const () = &raw const **vp_ctx;
let bytes = std::ptr::slice_from_raw_parts(slf, 1);
let _x = foo(bytes);
}

fn foo(bytes: *const [()]) -> *mut () {
bytes as *mut ()
}
180 changes: 180 additions & 0 deletions tests/mir-opt/dont_reset_cast_kind_without_updating_operand.test.GVN.panic-abort.diff
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Original file line number Diff line number Diff line change
@@ -0,0 +1,180 @@
- // MIR for `test` before GVN
+ // MIR for `test` after GVN

fn test() -> () {
let mut _0: ();
let _1: &std::boxed::Box<()>;
let _2: &std::boxed::Box<()>;
let _3: std::boxed::Box<()>;
let mut _6: *const ();
let mut _8: *const [()];
let mut _9: std::boxed::Box<()>;
let mut _10: *const ();
let mut _23: usize;
scope 1 {
debug vp_ctx => _1;
let _4: *const ();
scope 2 {
debug slf => _10;
let _5: *const [()];
scope 3 {
debug bytes => _5;
let _7: *mut ();
scope 4 {
debug _x => _7;
}
scope 18 (inlined foo) {
}
}
scope 16 (inlined slice_from_raw_parts::<()>) {
scope 17 (inlined std::ptr::from_raw_parts::<[()], ()>) {
}
}
}
}
scope 5 (inlined Box::<()>::new) {
let mut _11: usize;
let mut _12: usize;
let mut _13: *mut u8;
scope 6 (inlined alloc::alloc::exchange_malloc) {
let _14: std::alloc::Layout;
let mut _15: std::result::Result<std::ptr::NonNull<[u8]>, std::alloc::AllocError>;
let mut _16: isize;
let mut _18: !;
scope 7 {
let _17: std::ptr::NonNull<[u8]>;
scope 8 {
scope 11 (inlined NonNull::<[u8]>::as_mut_ptr) {
scope 12 (inlined NonNull::<[u8]>::as_non_null_ptr) {
scope 13 (inlined NonNull::<[u8]>::cast::<u8>) {
let mut _22: *mut [u8];
scope 14 (inlined NonNull::<[u8]>::as_ptr) {
}
}
}
scope 15 (inlined NonNull::<u8>::as_ptr) {
}
}
}
scope 10 (inlined <std::alloc::Global as Allocator>::allocate) {
}
}
scope 9 (inlined Layout::from_size_align_unchecked) {
let mut _19: bool;
let _20: ();
let mut _21: std::ptr::Alignment;
}
}
}

bb0: {
StorageLive(_1);
- StorageLive(_2);
+ nop;
StorageLive(_3);
StorageLive(_11);
StorageLive(_12);
StorageLive(_13);
- _11 = SizeOf(());
- _12 = AlignOf(());
+ _11 = const 0_usize;
+ _12 = const 1_usize;
StorageLive(_14);
StorageLive(_16);
StorageLive(_17);
StorageLive(_19);
_19 = const false;
- switchInt(move _19) -> [0: bb6, otherwise: bb5];
+ switchInt(const false) -> [0: bb6, otherwise: bb5];
}

bb1: {
StorageDead(_3);
StorageDead(_1);
return;
}

bb2: {
unreachable;
}

bb3: {
- _18 = handle_alloc_error(move _14) -> unwind unreachable;
+ _18 = handle_alloc_error(const Layout {{ size: 0_usize, align: std::ptr::Alignment(std::ptr::alignment::AlignmentEnum::_Align1Shl0) }}) -> unwind unreachable;
}

bb4: {
_17 = copy ((_15 as Ok).0: std::ptr::NonNull<[u8]>);
StorageLive(_22);
_22 = copy _17 as *mut [u8] (Transmute);
_13 = copy _22 as *mut u8 (PtrToPtr);
StorageDead(_22);
StorageDead(_15);
StorageDead(_17);
StorageDead(_16);
StorageDead(_14);
_3 = ShallowInitBox(move _13, ());
StorageDead(_13);
StorageDead(_12);
StorageDead(_11);
_2 = &_3;
_1 = copy _2;
- StorageDead(_2);
+ nop;
StorageLive(_4);
- _9 = deref_copy _3;
+ _9 = copy _3;
_10 = copy ((_9.0: std::ptr::Unique<()>).0: std::ptr::NonNull<()>) as *const () (Transmute);
_4 = copy _10;
- StorageLive(_5);
+ nop;
StorageLive(_6);
- _6 = copy _4;
+ _6 = copy _10;
StorageLive(_23);
_23 = const 1_usize;
- _5 = *const [()] from (copy _6, copy _23);
+ _5 = *const [()] from (copy _10, const 1_usize);
StorageDead(_23);
StorageDead(_6);
StorageLive(_7);
StorageLive(_8);
_8 = copy _5;
- _7 = copy _8 as *mut () (PtrToPtr);
+ _7 = copy _5 as *mut () (PtrToPtr);
StorageDead(_8);
StorageDead(_7);
- StorageDead(_5);
+ nop;
StorageDead(_4);
drop(_3) -> [return: bb1, unwind unreachable];
}

bb5: {
- _20 = Layout::from_size_align_unchecked::precondition_check(copy _11, copy _12) -> [return: bb6, unwind unreachable];
+ _20 = Layout::from_size_align_unchecked::precondition_check(const 0_usize, const 1_usize) -> [return: bb6, unwind unreachable];
}

bb6: {
StorageDead(_19);
StorageLive(_21);
- _21 = copy _12 as std::ptr::Alignment (Transmute);
- _14 = Layout { size: copy _11, align: move _21 };
+ _21 = const std::ptr::Alignment(std::ptr::alignment::AlignmentEnum::_Align1Shl0);
+ _14 = const Layout {{ size: 0_usize, align: std::ptr::Alignment(std::ptr::alignment::AlignmentEnum::_Align1Shl0) }};
StorageDead(_21);
StorageLive(_15);
- _15 = std::alloc::Global::alloc_impl(const alloc::alloc::exchange_malloc::promoted[0], copy _14, const false) -> [return: bb7, unwind unreachable];
+ _15 = std::alloc::Global::alloc_impl(const alloc::alloc::exchange_malloc::promoted[0], const Layout {{ size: 0_usize, align: std::ptr::Alignment(std::ptr::alignment::AlignmentEnum::_Align1Shl0) }}, const false) -> [return: bb7, unwind unreachable];
}

bb7: {
_16 = discriminant(_15);
switchInt(move _16) -> [0: bb4, 1: bb3, otherwise: bb2];
}
+ }
+
+ ALLOC0 (size: 8, align: 4) {
+ 01 00 00 00 00 00 00 00 │ ........
}

88 changes: 88 additions & 0 deletions tests/mir-opt/dont_reset_cast_kind_without_updating_operand.test.GVN.panic-unwind.diff
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Original file line number Diff line number Diff line change
@@ -0,0 +1,88 @@
- // MIR for `test` before GVN
+ // MIR for `test` after GVN

fn test() -> () {
let mut _0: ();
let _1: &std::boxed::Box<()>;
let _2: &std::boxed::Box<()>;
let _3: std::boxed::Box<()>;
let mut _6: *const ();
let mut _8: *const [()];
let mut _9: std::boxed::Box<()>;
let mut _10: *const ();
let mut _11: usize;
scope 1 {
debug vp_ctx => _1;
let _4: *const ();
scope 2 {
debug slf => _10;
let _5: *const [()];
scope 3 {
debug bytes => _5;
let _7: *mut ();
scope 4 {
debug _x => _7;
}
scope 7 (inlined foo) {
}
}
scope 5 (inlined slice_from_raw_parts::<()>) {
scope 6 (inlined std::ptr::from_raw_parts::<[()], ()>) {
}
}
}
}

bb0: {
StorageLive(_1);
- StorageLive(_2);
+ nop;
StorageLive(_3);
_3 = Box::<()>::new(const ()) -> [return: bb1, unwind continue];
}

bb1: {
_2 = &_3;
_1 = copy _2;
- StorageDead(_2);
+ nop;
StorageLive(_4);
- _9 = deref_copy _3;
+ _9 = copy _3;
_10 = copy ((_9.0: std::ptr::Unique<()>).0: std::ptr::NonNull<()>) as *const () (Transmute);
_4 = copy _10;
- StorageLive(_5);
+ nop;
StorageLive(_6);
- _6 = copy _4;
+ _6 = copy _10;
StorageLive(_11);
_11 = const 1_usize;
- _5 = *const [()] from (copy _6, copy _11);
+ _5 = *const [()] from (copy _10, const 1_usize);
StorageDead(_11);
StorageDead(_6);
StorageLive(_7);
StorageLive(_8);
_8 = copy _5;
- _7 = copy _8 as *mut () (PtrToPtr);
+ _7 = copy _5 as *mut () (PtrToPtr);
StorageDead(_8);
StorageDead(_7);
- StorageDead(_5);
+ nop;
StorageDead(_4);
drop(_3) -> [return: bb2, unwind: bb3];
}

bb2: {
StorageDead(_3);
StorageDead(_1);
return;
}

bb3 (cleanup): {
resume;
}
}

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