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Do not merge fn pointer casts.

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This commit is contained in:
Camille GILLOT 2023-10-21 09:59:03 +00:00
parent ac0228da59
commit c4cc9ca060
5 changed files with 272 additions and 3 deletions
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9
compiler/rustc_mir_transform/src/gvn.rs
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@ -92,6 +92,7 @@ use rustc_index::IndexVec;
use rustc_macros::newtype_index;
use rustc_middle::mir::visit::*;
use rustc_middle::mir::*;
use rustc_middle::ty::adjustment::PointerCoercion;
use rustc_middle::ty::layout::LayoutOf;
use rustc_middle::ty::{self, Ty, TyCtxt, TypeAndMut};
use rustc_span::def_id::DefId;
@ -761,6 +762,14 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
Rvalue::Cast(kind, ref mut value, to) => {
let from = value.ty(self.local_decls, self.tcx);
let value = self.simplify_operand(value, location)?;
if let CastKind::PointerCoercion(
PointerCoercion::ReifyFnPointer | PointerCoercion::ClosureFnPointer(_),
) = kind
{
// Each reification of a generic fn may get a different pointer.
// Do not try to merge them.
return self.new_opaque();
}
Value::Cast { kind, value, from, to }
}
Rvalue::BinaryOp(op, box (ref mut lhs, ref mut rhs)) => {

5
src/tools/miri/tests/pass/function_pointers.rs
View File

@ -80,9 +80,8 @@ fn main() {
// but Miri currently uses a fixed address for monomorphic functions.
assert!(return_fn_ptr(i) == i);
assert!(return_fn_ptr(i) as unsafe fn() -> i32 == i as fn() -> i32 as unsafe fn() -> i32);
// We don't check anything for `f`. Miri gives it many different addresses
// but mir-opts can turn them into the same address.
let _val = return_fn_ptr(f) != f;
// Miri gives it many different addresses to different reifications of a generic function.
assert!(return_fn_ptr(f) != f);
// However, if we only turn `f` into a function pointer and use that pointer,
// it is equal to itself.
let f2 = f as fn() -> i32;

118
tests/mir-opt/gvn.fn_pointers.GVN.panic-abort.diff Normal file
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@ -0,0 +1,118 @@
- // MIR for `fn_pointers` before GVN
+ // MIR for `fn_pointers` after GVN
fn fn_pointers() -> () {
let mut _0: ();
let _1: fn(u8) -> u8;
let _2: ();
let mut _3: fn(u8) -> u8;
let _5: ();
let mut _6: fn(u8) -> u8;
let mut _9: {closure@$DIR/gvn.rs:591:19: 591:21};
let _10: ();
let mut _11: fn();
let mut _13: {closure@$DIR/gvn.rs:591:19: 591:21};
let _14: ();
let mut _15: fn();
scope 1 {
debug f => _1;
let _4: fn(u8) -> u8;
scope 2 {
debug g => _4;
let _7: {closure@$DIR/gvn.rs:591:19: 591:21};
scope 3 {
debug closure => _7;
let _8: fn();
scope 4 {
debug cf => _8;
let _12: fn();
scope 5 {
debug cg => _12;
}
}
}
}
}
bb0: {
- StorageLive(_1);
+ nop;
_1 = identity::<u8> as fn(u8) -> u8 (PointerCoercion(ReifyFnPointer));
StorageLive(_2);
StorageLive(_3);
_3 = _1;
- _2 = opaque::<fn(u8) -> u8>(move _3) -> [return: bb1, unwind unreachable];
+ _2 = opaque::<fn(u8) -> u8>(_1) -> [return: bb1, unwind unreachable];
}
bb1: {
StorageDead(_3);
StorageDead(_2);
- StorageLive(_4);
+ nop;
_4 = identity::<u8> as fn(u8) -> u8 (PointerCoercion(ReifyFnPointer));
StorageLive(_5);
StorageLive(_6);
_6 = _4;
- _5 = opaque::<fn(u8) -> u8>(move _6) -> [return: bb2, unwind unreachable];
+ _5 = opaque::<fn(u8) -> u8>(_4) -> [return: bb2, unwind unreachable];
}
bb2: {
StorageDead(_6);
StorageDead(_5);
- StorageLive(_7);
- _7 = {closure@$DIR/gvn.rs:591:19: 591:21};
- StorageLive(_8);
+ nop;
+ _7 = const ZeroSized: {closure@$DIR/gvn.rs:591:19: 591:21};
+ nop;
StorageLive(_9);
- _9 = _7;
- _8 = move _9 as fn() (PointerCoercion(ClosureFnPointer(Normal)));
+ _9 = const ZeroSized: {closure@$DIR/gvn.rs:591:19: 591:21};
+ _8 = const ZeroSized: {closure@$DIR/gvn.rs:591:19: 591:21} as fn() (PointerCoercion(ClosureFnPointer(Normal)));
StorageDead(_9);
StorageLive(_10);
StorageLive(_11);
_11 = _8;
- _10 = opaque::<fn()>(move _11) -> [return: bb3, unwind unreachable];
+ _10 = opaque::<fn()>(_8) -> [return: bb3, unwind unreachable];
}
bb3: {
StorageDead(_11);
StorageDead(_10);
- StorageLive(_12);
+ nop;
StorageLive(_13);
- _13 = _7;
- _12 = move _13 as fn() (PointerCoercion(ClosureFnPointer(Normal)));
+ _13 = const ZeroSized: {closure@$DIR/gvn.rs:591:19: 591:21};
+ _12 = const ZeroSized: {closure@$DIR/gvn.rs:591:19: 591:21} as fn() (PointerCoercion(ClosureFnPointer(Normal)));
StorageDead(_13);
StorageLive(_14);
StorageLive(_15);
_15 = _12;
- _14 = opaque::<fn()>(move _15) -> [return: bb4, unwind unreachable];
+ _14 = opaque::<fn()>(_12) -> [return: bb4, unwind unreachable];
}
bb4: {
StorageDead(_15);
StorageDead(_14);
_0 = const ();
- StorageDead(_12);
- StorageDead(_8);
- StorageDead(_7);
- StorageDead(_4);
- StorageDead(_1);
+ nop;
+ nop;
+ nop;
+ nop;
+ nop;
return;
}
}

118
tests/mir-opt/gvn.fn_pointers.GVN.panic-unwind.diff Normal file
View File

@ -0,0 +1,118 @@
- // MIR for `fn_pointers` before GVN
+ // MIR for `fn_pointers` after GVN
fn fn_pointers() -> () {
let mut _0: ();
let _1: fn(u8) -> u8;
let _2: ();
let mut _3: fn(u8) -> u8;
let _5: ();
let mut _6: fn(u8) -> u8;
let mut _9: {closure@$DIR/gvn.rs:591:19: 591:21};
let _10: ();
let mut _11: fn();
let mut _13: {closure@$DIR/gvn.rs:591:19: 591:21};
let _14: ();
let mut _15: fn();
scope 1 {
debug f => _1;
let _4: fn(u8) -> u8;
scope 2 {
debug g => _4;
let _7: {closure@$DIR/gvn.rs:591:19: 591:21};
scope 3 {
debug closure => _7;
let _8: fn();
scope 4 {
debug cf => _8;
let _12: fn();
scope 5 {
debug cg => _12;
}
}
}
}
}
bb0: {
- StorageLive(_1);
+ nop;
_1 = identity::<u8> as fn(u8) -> u8 (PointerCoercion(ReifyFnPointer));
StorageLive(_2);
StorageLive(_3);
_3 = _1;
- _2 = opaque::<fn(u8) -> u8>(move _3) -> [return: bb1, unwind continue];
+ _2 = opaque::<fn(u8) -> u8>(_1) -> [return: bb1, unwind continue];
}
bb1: {
StorageDead(_3);
StorageDead(_2);
- StorageLive(_4);
+ nop;
_4 = identity::<u8> as fn(u8) -> u8 (PointerCoercion(ReifyFnPointer));
StorageLive(_5);
StorageLive(_6);
_6 = _4;
- _5 = opaque::<fn(u8) -> u8>(move _6) -> [return: bb2, unwind continue];
+ _5 = opaque::<fn(u8) -> u8>(_4) -> [return: bb2, unwind continue];
}
bb2: {
StorageDead(_6);
StorageDead(_5);
- StorageLive(_7);
- _7 = {closure@$DIR/gvn.rs:591:19: 591:21};
- StorageLive(_8);
+ nop;
+ _7 = const ZeroSized: {closure@$DIR/gvn.rs:591:19: 591:21};
+ nop;
StorageLive(_9);
- _9 = _7;
- _8 = move _9 as fn() (PointerCoercion(ClosureFnPointer(Normal)));
+ _9 = const ZeroSized: {closure@$DIR/gvn.rs:591:19: 591:21};
+ _8 = const ZeroSized: {closure@$DIR/gvn.rs:591:19: 591:21} as fn() (PointerCoercion(ClosureFnPointer(Normal)));
StorageDead(_9);
StorageLive(_10);
StorageLive(_11);
_11 = _8;
- _10 = opaque::<fn()>(move _11) -> [return: bb3, unwind continue];
+ _10 = opaque::<fn()>(_8) -> [return: bb3, unwind continue];
}
bb3: {
StorageDead(_11);
StorageDead(_10);
- StorageLive(_12);
+ nop;
StorageLive(_13);
- _13 = _7;
- _12 = move _13 as fn() (PointerCoercion(ClosureFnPointer(Normal)));
+ _13 = const ZeroSized: {closure@$DIR/gvn.rs:591:19: 591:21};
+ _12 = const ZeroSized: {closure@$DIR/gvn.rs:591:19: 591:21} as fn() (PointerCoercion(ClosureFnPointer(Normal)));
StorageDead(_13);
StorageLive(_14);
StorageLive(_15);
_15 = _12;
- _14 = opaque::<fn()>(move _15) -> [return: bb4, unwind continue];
+ _14 = opaque::<fn()>(_12) -> [return: bb4, unwind continue];
}
bb4: {
StorageDead(_15);
StorageDead(_14);
_0 = const ();
- StorageDead(_12);
- StorageDead(_8);
- StorageDead(_7);
- StorageDead(_4);
- StorageDead(_1);
+ nop;
+ nop;
+ nop;
+ nop;
+ nop;
return;
}
}

25
tests/mir-opt/gvn.rs
View File

@ -574,6 +574,29 @@ fn repeat() {
let array = [val, val, val, val, val, val, val, val, val, val];
}
/// Verify that we do not merge fn pointers created by casts.
fn fn_pointers() {
// CHECK-LABEL: fn fn_pointers(
// CHECK: [[f:_.*]] = identity::<u8> as fn(u8) -> u8 (PointerCoercion(ReifyFnPointer
// CHECK: opaque::<fn(u8) -> u8>([[f]])
let f = identity as fn(u8) -> u8;
opaque(f);
// CHECK: [[g:_.*]] = identity::<u8> as fn(u8) -> u8 (PointerCoercion(ReifyFnPointer
// CHECK: opaque::<fn(u8) -> u8>([[g]])
let g = identity as fn(u8) -> u8;
opaque(g);
// CHECK: [[cf:_.*]] = const {{.*}} as fn() (PointerCoercion(ClosureFnPointer
// CHECK: opaque::<fn()>([[cf]])
let closure = || {};
let cf = closure as fn();
opaque(cf);
// CHECK: [[cg:_.*]] = const {{.*}} as fn() (PointerCoercion(ClosureFnPointer
// CHECK: opaque::<fn()>([[cg]])
let cg = closure as fn();
opaque(cg);
}
fn main() {
subexpression_elimination(2, 4, 5);
wrap_unwrap(5);
@ -590,6 +613,7 @@ fn main() {
let (direct, indirect) = duplicate_slice();
assert_eq!(direct, indirect);
repeat();
fn_pointers();
}
#[inline(never)]
@ -614,3 +638,4 @@ fn identity<T>(x: T) -> T {
// EMIT_MIR gvn.slices.GVN.diff
// EMIT_MIR gvn.duplicate_slice.GVN.diff
// EMIT_MIR gvn.repeat.GVN.diff
// EMIT_MIR gvn.fn_pointers.GVN.diff