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
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
use crate::traits::*;
use rustc_middle::mir;
use rustc_middle::mir::interpret::ErrorHandled;
use rustc_middle::ty::layout::{FnAbiOf, HasTyCtxt, TyAndLayout};
use rustc_middle::ty::{self, Instance, Ty, TypeFoldable, TypeVisitable};
use rustc_target::abi::call::{FnAbi, PassMode};

use std::iter;

use rustc_index::bit_set::BitSet;
use rustc_index::vec::IndexVec;

use self::debuginfo::{FunctionDebugContext, PerLocalVarDebugInfo};
use self::place::PlaceRef;
use rustc_middle::mir::traversal;

use self::operand::{OperandRef, OperandValue};

/// Master context for codegenning from MIR.
pub struct FunctionCx<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> {
    instance: Instance<'tcx>,

    mir: &'tcx mir::Body<'tcx>,

    debug_context: Option<FunctionDebugContext<Bx::DIScope, Bx::DILocation>>,

    llfn: Bx::Function,

    cx: &'a Bx::CodegenCx,

    fn_abi: &'tcx FnAbi<'tcx, Ty<'tcx>>,

    /// When unwinding is initiated, we have to store this personality
    /// value somewhere so that we can load it and re-use it in the
    /// resume instruction. The personality is (afaik) some kind of
    /// value used for C++ unwinding, which must filter by type: we
    /// don't really care about it very much. Anyway, this value
    /// contains an alloca into which the personality is stored and
    /// then later loaded when generating the DIVERGE_BLOCK.
    personality_slot: Option<PlaceRef<'tcx, Bx::Value>>,

    /// A backend `BasicBlock` for each MIR `BasicBlock`, created lazily
    /// as-needed (e.g. RPO reaching it or another block branching to it).
    // FIXME(eddyb) rename `llbbs` and other `ll`-prefixed things to use a
    // more backend-agnostic prefix such as `cg` (i.e. this would be `cgbbs`).
    cached_llbbs: IndexVec<mir::BasicBlock, Option<Bx::BasicBlock>>,

    /// The funclet status of each basic block
    cleanup_kinds: IndexVec<mir::BasicBlock, analyze::CleanupKind>,

    /// When targeting MSVC, this stores the cleanup info for each funclet BB.
    /// This is initialized at the same time as the `landing_pads` entry for the
    /// funclets' head block, i.e. when needed by an unwind / `cleanup_ret` edge.
    funclets: IndexVec<mir::BasicBlock, Option<Bx::Funclet>>,

    /// This stores the cached landing/cleanup pad block for a given BB.
    // FIXME(eddyb) rename this to `eh_pads`.
    landing_pads: IndexVec<mir::BasicBlock, Option<Bx::BasicBlock>>,

    /// Cached unreachable block
    unreachable_block: Option<Bx::BasicBlock>,

    /// Cached double unwind guarding block
    double_unwind_guard: Option<Bx::BasicBlock>,

    /// The location where each MIR arg/var/tmp/ret is stored. This is
    /// usually an `PlaceRef` representing an alloca, but not always:
    /// sometimes we can skip the alloca and just store the value
    /// directly using an `OperandRef`, which makes for tighter LLVM
    /// IR. The conditions for using an `OperandRef` are as follows:
    ///
    /// - the type of the local must be judged "immediate" by `is_llvm_immediate`
    /// - the operand must never be referenced indirectly
    ///     - we should not take its address using the `&` operator
    ///     - nor should it appear in a place path like `tmp.a`
    /// - the operand must be defined by an rvalue that can generate immediate
    ///   values
    ///
    /// Avoiding allocs can also be important for certain intrinsics,
    /// notably `expect`.
    locals: IndexVec<mir::Local, LocalRef<'tcx, Bx::Value>>,

    /// All `VarDebugInfo` from the MIR body, partitioned by `Local`.
    /// This is `None` if no var`#[non_exhaustive]`iable debuginfo/names are needed.
    per_local_var_debug_info:
        Option<IndexVec<mir::Local, Vec<PerLocalVarDebugInfo<'tcx, Bx::DIVariable>>>>,

    /// Caller location propagated if this function has `#[track_caller]`.
    caller_location: Option<OperandRef<'tcx, Bx::Value>>,
}

impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
    pub fn monomorphize<T>(&self, value: T) -> T
    where
        T: Copy + TypeFoldable<'tcx>,
    {
        debug!("monomorphize: self.instance={:?}", self.instance);
        self.instance.subst_mir_and_normalize_erasing_regions(
            self.cx.tcx(),
            ty::ParamEnv::reveal_all(),
            value,
        )
    }
}

enum LocalRef<'tcx, V> {
    Place(PlaceRef<'tcx, V>),
    /// `UnsizedPlace(p)`: `p` itself is a thin pointer (indirect place).
    /// `*p` is the fat pointer that references the actual unsized place.
    /// Every time it is initialized, we have to reallocate the place
    /// and update the fat pointer. That's the reason why it is indirect.
    UnsizedPlace(PlaceRef<'tcx, V>),
    Operand(Option<OperandRef<'tcx, V>>),
}

impl<'a, 'tcx, V: CodegenObject> LocalRef<'tcx, V> {
    fn new_operand<Bx: BuilderMethods<'a, 'tcx, Value = V>>(
        bx: &mut Bx,
        layout: TyAndLayout<'tcx>,
    ) -> LocalRef<'tcx, V> {
        if layout.is_zst() {
            // Zero-size temporaries aren't always initialized, which
            // doesn't matter because they don't contain data, but
            // we need something in the operand.
            LocalRef::Operand(Some(OperandRef::new_zst(bx, layout)))
        } else {
            LocalRef::Operand(None)
        }
    }
}

///////////////////////////////////////////////////////////////////////////

#[instrument(level = "debug", skip(cx))]
pub fn codegen_mir<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
    cx: &'a Bx::CodegenCx,
    instance: Instance<'tcx>,
) {
    assert!(!instance.substs.needs_infer());

    let llfn = cx.get_fn(instance);

    let mir = cx.tcx().instance_mir(instance.def);

    let fn_abi = cx.fn_abi_of_instance(instance, ty::List::empty());
    debug!("fn_abi: {:?}", fn_abi);

    let debug_context = cx.create_function_debug_context(instance, &fn_abi, llfn, &mir);

    let start_llbb = Bx::append_block(cx, llfn, "start");
    let mut bx = Bx::build(cx, start_llbb);

    if mir.basic_blocks.iter().any(|bb| bb.is_cleanup) {
        bx.set_personality_fn(cx.eh_personality());
    }

    let cleanup_kinds = analyze::cleanup_kinds(&mir);
    let cached_llbbs: IndexVec<mir::BasicBlock, Option<Bx::BasicBlock>> = mir
        .basic_blocks
        .indices()
        .map(|bb| if bb == mir::START_BLOCK { Some(start_llbb) } else { None })
        .collect();

    let mut fx = FunctionCx {
        instance,
        mir,
        llfn,
        fn_abi,
        cx,
        personality_slot: None,
        cached_llbbs,
        unreachable_block: None,
        double_unwind_guard: None,
        cleanup_kinds,
        landing_pads: IndexVec::from_elem(None, &mir.basic_blocks),
        funclets: IndexVec::from_fn_n(|_| None, mir.basic_blocks.len()),
        locals: IndexVec::new(),
        debug_context,
        per_local_var_debug_info: None,
        caller_location: None,
    };

    fx.per_local_var_debug_info = fx.compute_per_local_var_debug_info(&mut bx);

    // Evaluate all required consts; codegen later assumes that CTFE will never fail.
    let mut all_consts_ok = true;
    for const_ in &mir.required_consts {
        if let Err(err) = fx.eval_mir_constant(const_) {
            all_consts_ok = false;
            match err {
                // errored or at least linted
                ErrorHandled::Reported(_) | ErrorHandled::Linted => {}
                ErrorHandled::TooGeneric => {
                    span_bug!(const_.span, "codegen encountered polymorphic constant: {:?}", err)
                }
            }
        }
    }
    if !all_consts_ok {
        // We leave the IR in some half-built state here, and rely on this code not even being
        // submitted to LLVM once an error was raised.
        return;
    }

    let memory_locals = analyze::non_ssa_locals(&fx);

    // Allocate variable and temp allocas
    fx.locals = {
        let args = arg_local_refs(&mut bx, &mut fx, &memory_locals);

        let mut allocate_local = |local| {
            let decl = &mir.local_decls[local];
            let layout = bx.layout_of(fx.monomorphize(decl.ty));
            assert!(!layout.ty.has_erasable_regions());

            if local == mir::RETURN_PLACE && fx.fn_abi.ret.is_indirect() {
                debug!("alloc: {:?} (return place) -> place", local);
                let llretptr = bx.get_param(0);
                return LocalRef::Place(PlaceRef::new_sized(llretptr, layout));
            }

            if memory_locals.contains(local) {
                debug!("alloc: {:?} -> place", local);
                if layout.is_unsized() {
                    LocalRef::UnsizedPlace(PlaceRef::alloca_unsized_indirect(&mut bx, layout))
                } else {
                    LocalRef::Place(PlaceRef::alloca(&mut bx, layout))
                }
            } else {
                debug!("alloc: {:?} -> operand", local);
                LocalRef::new_operand(&mut bx, layout)
            }
        };

        let retptr = allocate_local(mir::RETURN_PLACE);
        iter::once(retptr)
            .chain(args.into_iter())
            .chain(mir.vars_and_temps_iter().map(allocate_local))
            .collect()
    };

    // Apply debuginfo to the newly allocated locals.
    fx.debug_introduce_locals(&mut bx);

    // Codegen the body of each block using reverse postorder
    for (bb, _) in traversal::reverse_postorder(&mir) {
        fx.codegen_block(bb);
    }
}

/// Produces, for each argument, a `Value` pointing at the
/// argument's value. As arguments are places, these are always
/// indirect.
fn arg_local_refs<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
    bx: &mut Bx,
    fx: &mut FunctionCx<'a, 'tcx, Bx>,
    memory_locals: &BitSet<mir::Local>,
) -> Vec<LocalRef<'tcx, Bx::Value>> {
    let mir = fx.mir;
    let mut idx = 0;
    let mut llarg_idx = fx.fn_abi.ret.is_indirect() as usize;

    let mut num_untupled = None;

    let args = mir
        .args_iter()
        .enumerate()
        .map(|(arg_index, local)| {
            let arg_decl = &mir.local_decls[local];

            if Some(local) == mir.spread_arg {
                // This argument (e.g., the last argument in the "rust-call" ABI)
                // is a tuple that was spread at the ABI level and now we have
                // to reconstruct it into a tuple local variable, from multiple
                // individual LLVM function arguments.

                let arg_ty = fx.monomorphize(arg_decl.ty);
                let ty::Tuple(tupled_arg_tys) = arg_ty.kind() else {
                    bug!("spread argument isn't a tuple?!");
                };

                let place = PlaceRef::alloca(bx, bx.layout_of(arg_ty));
                for i in 0..tupled_arg_tys.len() {
                    let arg = &fx.fn_abi.args[idx];
                    idx += 1;
                    if let PassMode::Cast(_, true) = arg.mode {
                        llarg_idx += 1;
                    }
                    let pr_field = place.project_field(bx, i);
                    bx.store_fn_arg(arg, &mut llarg_idx, pr_field);
                }
                assert_eq!(
                    None,
                    num_untupled.replace(tupled_arg_tys.len()),
                    "Replaced existing num_tupled"
                );

                return LocalRef::Place(place);
            }

            if fx.fn_abi.c_variadic && arg_index == fx.fn_abi.args.len() {
                let arg_ty = fx.monomorphize(arg_decl.ty);

                let va_list = PlaceRef::alloca(bx, bx.layout_of(arg_ty));
                bx.va_start(va_list.llval);

                return LocalRef::Place(va_list);
            }

            let arg = &fx.fn_abi.args[idx];
            idx += 1;
            if let PassMode::Cast(_, true) = arg.mode {
                llarg_idx += 1;
            }

            if !memory_locals.contains(local) {
                // We don't have to cast or keep the argument in the alloca.
                // FIXME(eddyb): We should figure out how to use llvm.dbg.value instead
                // of putting everything in allocas just so we can use llvm.dbg.declare.
                let local = |op| LocalRef::Operand(Some(op));
                match arg.mode {
                    PassMode::Ignore => {
                        return local(OperandRef::new_zst(bx, arg.layout));
                    }
                    PassMode::Direct(_) => {
                        let llarg = bx.get_param(llarg_idx);
                        llarg_idx += 1;
                        return local(OperandRef::from_immediate_or_packed_pair(
                            bx, llarg, arg.layout,
                        ));
                    }
                    PassMode::Pair(..) => {
                        let (a, b) = (bx.get_param(llarg_idx), bx.get_param(llarg_idx + 1));
                        llarg_idx += 2;

                        return local(OperandRef {
                            val: OperandValue::Pair(a, b),
                            layout: arg.layout,
                        });
                    }
                    _ => {}
                }
            }

            if arg.is_sized_indirect() {
                // Don't copy an indirect argument to an alloca, the caller
                // already put it in a temporary alloca and gave it up.
                // FIXME: lifetimes
                let llarg = bx.get_param(llarg_idx);
                llarg_idx += 1;
                LocalRef::Place(PlaceRef::new_sized(llarg, arg.layout))
            } else if arg.is_unsized_indirect() {
                // As the storage for the indirect argument lives during
                // the whole function call, we just copy the fat pointer.
                let llarg = bx.get_param(llarg_idx);
                llarg_idx += 1;
                let llextra = bx.get_param(llarg_idx);
                llarg_idx += 1;
                let indirect_operand = OperandValue::Pair(llarg, llextra);

                let tmp = PlaceRef::alloca_unsized_indirect(bx, arg.layout);
                indirect_operand.store(bx, tmp);
                LocalRef::UnsizedPlace(tmp)
            } else {
                let tmp = PlaceRef::alloca(bx, arg.layout);
                bx.store_fn_arg(arg, &mut llarg_idx, tmp);
                LocalRef::Place(tmp)
            }
        })
        .collect::<Vec<_>>();

    if fx.instance.def.requires_caller_location(bx.tcx()) {
        let mir_args = if let Some(num_untupled) = num_untupled {
            // Subtract off the tupled argument that gets 'expanded'
            args.len() - 1 + num_untupled
        } else {
            args.len()
        };
        assert_eq!(
            fx.fn_abi.args.len(),
            mir_args + 1,
            "#[track_caller] instance {:?} must have 1 more argument in their ABI than in their MIR",
            fx.instance
        );

        let arg = fx.fn_abi.args.last().unwrap();
        match arg.mode {
            PassMode::Direct(_) => (),
            _ => bug!("caller location must be PassMode::Direct, found {:?}", arg.mode),
        }

        fx.caller_location = Some(OperandRef {
            val: OperandValue::Immediate(bx.get_param(llarg_idx)),
            layout: arg.layout,
        });
    }

    args
}

mod analyze;
mod block;
pub mod constant;
pub mod coverageinfo;
pub mod debuginfo;
mod intrinsic;
pub mod operand;
pub mod place;
mod rvalue;
mod statement;