1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
//! Performs various peephole optimizations.

use rustc_ast::attr;
use rustc_hir::LangItem;
use rustc_middle::bug;
use rustc_middle::mir::*;
use rustc_middle::ty::layout::ValidityRequirement;
use rustc_middle::ty::{self, layout, GenericArgsRef, ParamEnv, Ty, TyCtxt};
use rustc_span::sym;
use rustc_span::symbol::Symbol;
use rustc_target::spec::abi::Abi;

use crate::simplify::simplify_duplicate_switch_targets;
use crate::take_array;

pub enum InstSimplify {
    BeforeInline,
    AfterSimplifyCfg,
}

impl InstSimplify {
    pub fn name(&self) -> &'static str {
        match self {
            InstSimplify::BeforeInline => "InstSimplify-before-inline",
            InstSimplify::AfterSimplifyCfg => "InstSimplify-after-simplifycfg",
        }
    }
}

impl<'tcx> MirPass<'tcx> for InstSimplify {
    fn name(&self) -> &'static str {
        self.name()
    }

    fn is_enabled(&self, sess: &rustc_session::Session) -> bool {
        sess.mir_opt_level() > 0
    }

    fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
        let ctx = InstSimplifyContext {
            tcx,
            local_decls: &body.local_decls,
            param_env: tcx.param_env_reveal_all_normalized(body.source.def_id()),
        };
        let preserve_ub_checks =
            attr::contains_name(tcx.hir().krate_attrs(), sym::rustc_preserve_ub_checks);
        for block in body.basic_blocks.as_mut() {
            for statement in block.statements.iter_mut() {
                match statement.kind {
                    StatementKind::Assign(box (_place, ref mut rvalue)) => {
                        if !preserve_ub_checks {
                            ctx.simplify_ub_check(&statement.source_info, rvalue);
                        }
                        ctx.simplify_bool_cmp(&statement.source_info, rvalue);
                        ctx.simplify_ref_deref(&statement.source_info, rvalue);
                        ctx.simplify_len(&statement.source_info, rvalue);
                        ctx.simplify_ptr_aggregate(&statement.source_info, rvalue);
                        ctx.simplify_cast(rvalue);
                    }
                    _ => {}
                }
            }

            ctx.simplify_primitive_clone(block.terminator.as_mut().unwrap(), &mut block.statements);
            ctx.simplify_intrinsic_assert(block.terminator.as_mut().unwrap());
            ctx.simplify_nounwind_call(block.terminator.as_mut().unwrap());
            simplify_duplicate_switch_targets(block.terminator.as_mut().unwrap());
        }
    }
}

struct InstSimplifyContext<'tcx, 'a> {
    tcx: TyCtxt<'tcx>,
    local_decls: &'a LocalDecls<'tcx>,
    param_env: ParamEnv<'tcx>,
}

impl<'tcx> InstSimplifyContext<'tcx, '_> {
    fn should_simplify(&self, source_info: &SourceInfo, rvalue: &Rvalue<'tcx>) -> bool {
        self.should_simplify_custom(source_info, "Rvalue", rvalue)
    }

    fn should_simplify_custom(
        &self,
        source_info: &SourceInfo,
        label: &str,
        value: impl std::fmt::Debug,
    ) -> bool {
        self.tcx.consider_optimizing(|| {
            format!("InstSimplify - {label}: {value:?} SourceInfo: {source_info:?}")
        })
    }

    /// Transform boolean comparisons into logical operations.
    fn simplify_bool_cmp(&self, source_info: &SourceInfo, rvalue: &mut Rvalue<'tcx>) {
        match rvalue {
            Rvalue::BinaryOp(op @ (BinOp::Eq | BinOp::Ne), box (a, b)) => {
                let new = match (op, self.try_eval_bool(a), self.try_eval_bool(b)) {
                    // Transform "Eq(a, true)" ==> "a"
                    (BinOp::Eq, _, Some(true)) => Some(Rvalue::Use(a.clone())),

                    // Transform "Ne(a, false)" ==> "a"
                    (BinOp::Ne, _, Some(false)) => Some(Rvalue::Use(a.clone())),

                    // Transform "Eq(true, b)" ==> "b"
                    (BinOp::Eq, Some(true), _) => Some(Rvalue::Use(b.clone())),

                    // Transform "Ne(false, b)" ==> "b"
                    (BinOp::Ne, Some(false), _) => Some(Rvalue::Use(b.clone())),

                    // Transform "Eq(false, b)" ==> "Not(b)"
                    (BinOp::Eq, Some(false), _) => Some(Rvalue::UnaryOp(UnOp::Not, b.clone())),

                    // Transform "Ne(true, b)" ==> "Not(b)"
                    (BinOp::Ne, Some(true), _) => Some(Rvalue::UnaryOp(UnOp::Not, b.clone())),

                    // Transform "Eq(a, false)" ==> "Not(a)"
                    (BinOp::Eq, _, Some(false)) => Some(Rvalue::UnaryOp(UnOp::Not, a.clone())),

                    // Transform "Ne(a, true)" ==> "Not(a)"
                    (BinOp::Ne, _, Some(true)) => Some(Rvalue::UnaryOp(UnOp::Not, a.clone())),

                    _ => None,
                };

                if let Some(new) = new
                    && self.should_simplify(source_info, rvalue)
                {
                    *rvalue = new;
                }
            }

            _ => {}
        }
    }

    fn try_eval_bool(&self, a: &Operand<'_>) -> Option<bool> {
        let a = a.constant()?;
        if a.const_.ty().is_bool() { a.const_.try_to_bool() } else { None }
    }

    /// Transform `&(*a)` ==> `a`.
    fn simplify_ref_deref(&self, source_info: &SourceInfo, rvalue: &mut Rvalue<'tcx>) {
        if let Rvalue::Ref(_, _, place) | Rvalue::RawPtr(_, place) = rvalue {
            if let Some((base, ProjectionElem::Deref)) = place.as_ref().last_projection() {
                if rvalue.ty(self.local_decls, self.tcx) != base.ty(self.local_decls, self.tcx).ty {
                    return;
                }

                if !self.should_simplify(source_info, rvalue) {
                    return;
                }

                *rvalue = Rvalue::Use(Operand::Copy(Place {
                    local: base.local,
                    projection: self.tcx.mk_place_elems(base.projection),
                }));
            }
        }
    }

    /// Transform `Len([_; N])` ==> `N`.
    fn simplify_len(&self, source_info: &SourceInfo, rvalue: &mut Rvalue<'tcx>) {
        if let Rvalue::Len(ref place) = *rvalue {
            let place_ty = place.ty(self.local_decls, self.tcx).ty;
            if let ty::Array(_, len) = *place_ty.kind() {
                if !self.should_simplify(source_info, rvalue) {
                    return;
                }

                let const_ = Const::from_ty_const(len, self.tcx.types.usize, self.tcx);
                let constant = ConstOperand { span: source_info.span, const_, user_ty: None };
                *rvalue = Rvalue::Use(Operand::Constant(Box::new(constant)));
            }
        }
    }

    /// Transform `Aggregate(RawPtr, [p, ()])` ==> `Cast(PtrToPtr, p)`.
    fn simplify_ptr_aggregate(&self, source_info: &SourceInfo, rvalue: &mut Rvalue<'tcx>) {
        if let Rvalue::Aggregate(box AggregateKind::RawPtr(pointee_ty, mutability), fields) = rvalue
        {
            let meta_ty = fields.raw[1].ty(self.local_decls, self.tcx);
            if meta_ty.is_unit() {
                // The mutable borrows we're holding prevent printing `rvalue` here
                if !self.should_simplify_custom(
                    source_info,
                    "Aggregate::RawPtr",
                    (&pointee_ty, *mutability, &fields),
                ) {
                    return;
                }

                let mut fields = std::mem::take(fields);
                let _meta = fields.pop().unwrap();
                let data = fields.pop().unwrap();
                let ptr_ty = Ty::new_ptr(self.tcx, *pointee_ty, *mutability);
                *rvalue = Rvalue::Cast(CastKind::PtrToPtr, data, ptr_ty);
            }
        }
    }

    fn simplify_ub_check(&self, source_info: &SourceInfo, rvalue: &mut Rvalue<'tcx>) {
        if let Rvalue::NullaryOp(NullOp::UbChecks, _) = *rvalue {
            let const_ = Const::from_bool(self.tcx, self.tcx.sess.ub_checks());
            let constant = ConstOperand { span: source_info.span, const_, user_ty: None };
            *rvalue = Rvalue::Use(Operand::Constant(Box::new(constant)));
        }
    }

    fn simplify_cast(&self, rvalue: &mut Rvalue<'tcx>) {
        if let Rvalue::Cast(kind, operand, cast_ty) = rvalue {
            let operand_ty = operand.ty(self.local_decls, self.tcx);
            if operand_ty == *cast_ty {
                *rvalue = Rvalue::Use(operand.clone());
            } else if *kind == CastKind::Transmute {
                // Transmuting an integer to another integer is just a signedness cast
                if let (ty::Int(int), ty::Uint(uint)) | (ty::Uint(uint), ty::Int(int)) =
                    (operand_ty.kind(), cast_ty.kind())
                    && int.bit_width() == uint.bit_width()
                {
                    // The width check isn't strictly necessary, as different widths
                    // are UB and thus we'd be allowed to turn it into a cast anyway.
                    // But let's keep the UB around for codegen to exploit later.
                    // (If `CastKind::Transmute` ever becomes *not* UB for mismatched sizes,
                    // then the width check is necessary for big-endian correctness.)
                    *kind = CastKind::IntToInt;
                    return;
                }

                // Transmuting a transparent struct/union to a field's type is a projection
                if let ty::Adt(adt_def, args) = operand_ty.kind()
                    && adt_def.repr().transparent()
                    && (adt_def.is_struct() || adt_def.is_union())
                    && let Some(place) = operand.place()
                {
                    let variant = adt_def.non_enum_variant();
                    for (i, field) in variant.fields.iter_enumerated() {
                        let field_ty = field.ty(self.tcx, args);
                        if field_ty == *cast_ty {
                            let place = place
                                .project_deeper(&[ProjectionElem::Field(i, *cast_ty)], self.tcx);
                            let operand = if operand.is_move() {
                                Operand::Move(place)
                            } else {
                                Operand::Copy(place)
                            };
                            *rvalue = Rvalue::Use(operand);
                            return;
                        }
                    }
                }
            }
        }
    }

    fn simplify_primitive_clone(
        &self,
        terminator: &mut Terminator<'tcx>,
        statements: &mut Vec<Statement<'tcx>>,
    ) {
        let TerminatorKind::Call { func, args, destination, target, .. } = &mut terminator.kind
        else {
            return;
        };

        // It's definitely not a clone if there are multiple arguments
        let [arg] = &args[..] else { return };

        let Some(destination_block) = *target else { return };

        // Only bother looking more if it's easy to know what we're calling
        let Some((fn_def_id, fn_args)) = func.const_fn_def() else { return };

        // Clone needs one arg, so we can cheaply rule out other stuff
        if fn_args.len() != 1 {
            return;
        }

        // These types are easily available from locals, so check that before
        // doing DefId lookups to figure out what we're actually calling.
        let arg_ty = arg.node.ty(self.local_decls, self.tcx);

        let ty::Ref(_region, inner_ty, Mutability::Not) = *arg_ty.kind() else { return };

        if !inner_ty.is_trivially_pure_clone_copy() {
            return;
        }

        if !self.tcx.is_lang_item(fn_def_id, LangItem::CloneFn) {
            return;
        }

        if !self.tcx.consider_optimizing(|| {
            format!(
                "InstSimplify - Call: {:?} SourceInfo: {:?}",
                (fn_def_id, fn_args),
                terminator.source_info
            )
        }) {
            return;
        }

        let Ok([arg]) = take_array(args) else { return };
        let Some(arg_place) = arg.node.place() else { return };

        statements.push(Statement {
            source_info: terminator.source_info,
            kind: StatementKind::Assign(Box::new((
                *destination,
                Rvalue::Use(Operand::Copy(
                    arg_place.project_deeper(&[ProjectionElem::Deref], self.tcx),
                )),
            ))),
        });
        terminator.kind = TerminatorKind::Goto { target: destination_block };
    }

    fn simplify_nounwind_call(&self, terminator: &mut Terminator<'tcx>) {
        let TerminatorKind::Call { func, unwind, .. } = &mut terminator.kind else {
            return;
        };

        let Some((def_id, _)) = func.const_fn_def() else {
            return;
        };

        let body_ty = self.tcx.type_of(def_id).skip_binder();
        let body_abi = match body_ty.kind() {
            ty::FnDef(..) => body_ty.fn_sig(self.tcx).abi(),
            ty::Closure(..) => Abi::RustCall,
            ty::Coroutine(..) => Abi::Rust,
            _ => bug!("unexpected body ty: {:?}", body_ty),
        };

        if !layout::fn_can_unwind(self.tcx, Some(def_id), body_abi) {
            *unwind = UnwindAction::Unreachable;
        }
    }

    fn simplify_intrinsic_assert(&self, terminator: &mut Terminator<'tcx>) {
        let TerminatorKind::Call { func, target, .. } = &mut terminator.kind else {
            return;
        };
        let Some(target_block) = target else {
            return;
        };
        let func_ty = func.ty(self.local_decls, self.tcx);
        let Some((intrinsic_name, args)) = resolve_rust_intrinsic(self.tcx, func_ty) else {
            return;
        };
        // The intrinsics we are interested in have one generic parameter
        if args.is_empty() {
            return;
        }

        let known_is_valid =
            intrinsic_assert_panics(self.tcx, self.param_env, args[0], intrinsic_name);
        match known_is_valid {
            // We don't know the layout or it's not validity assertion at all, don't touch it
            None => {}
            Some(true) => {
                // If we know the assert panics, indicate to later opts that the call diverges
                *target = None;
            }
            Some(false) => {
                // If we know the assert does not panic, turn the call into a Goto
                terminator.kind = TerminatorKind::Goto { target: *target_block };
            }
        }
    }
}

fn intrinsic_assert_panics<'tcx>(
    tcx: TyCtxt<'tcx>,
    param_env: ty::ParamEnv<'tcx>,
    arg: ty::GenericArg<'tcx>,
    intrinsic_name: Symbol,
) -> Option<bool> {
    let requirement = ValidityRequirement::from_intrinsic(intrinsic_name)?;
    let ty = arg.expect_ty();
    Some(!tcx.check_validity_requirement((requirement, param_env.and(ty))).ok()?)
}

fn resolve_rust_intrinsic<'tcx>(
    tcx: TyCtxt<'tcx>,
    func_ty: Ty<'tcx>,
) -> Option<(Symbol, GenericArgsRef<'tcx>)> {
    if let ty::FnDef(def_id, args) = *func_ty.kind() {
        let intrinsic = tcx.intrinsic(def_id)?;
        return Some((intrinsic.name, args));
    }
    None
}