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RalfJungRalfJung
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explain PassMode::Cast
1 parent 5ede940 commit 6570039

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7 files changed

+38
-27
lines changed

7 files changed

+38
-27
lines changed

‎compiler/rustc_codegen_llvm/src/abi.rs

Lines changed: 10 additions & 8 deletions
Original file line numberDiff line numberDiff line change
@@ -211,7 +211,7 @@ impl<'ll, 'tcx> ArgAbiExt<'ll, 'tcx> for ArgAbi<'tcx, Ty<'tcx>> {
211211
OperandValue::Ref(val, None, self.layout.align.abi).store(bx, dst)
212212
} else if self.is_unsized_indirect() {
213213
bug!("unsized `ArgAbi` must be handled through `store_fn_arg`");
214-
} else if let PassMode::Cast(cast, _) = &self.mode {
214+
} else if let PassMode::Cast { cast, pad_i32: _ } = &self.mode {
215215
// FIXME(eddyb): Figure out when the simpler Store is safe, clang
216216
// uses it for i16 -> {i8, i8}, but not for i24 -> {i8, i8, i8}.
217217
let can_store_through_cast_ptr = false;
@@ -279,7 +279,7 @@ impl<'ll, 'tcx> ArgAbiExt<'ll, 'tcx> for ArgAbi<'tcx, Ty<'tcx>> {
279279
}
280280
PassMode::Direct(_)
281281
| PassMode::Indirect { attrs: _, extra_attrs: None, on_stack: _ }
282-
| PassMode::Cast(..) => {
282+
| PassMode::Cast { .. } => {
283283
let next_arg = next();
284284
self.store(bx, next_arg, dst);
285285
}
@@ -332,7 +332,7 @@ impl<'ll, 'tcx> FnAbiLlvmExt<'ll, 'tcx> for FnAbi<'tcx, Ty<'tcx>> {
332332
let llreturn_ty = match &self.ret.mode {
333333
PassMode::Ignore => cx.type_void(),
334334
PassMode::Direct(_) | PassMode::Pair(..) => self.ret.layout.immediate_llvm_type(cx),
335-
PassMode::Cast(cast, _) => cast.llvm_type(cx),
335+
PassMode::Cast { cast, pad_i32: _ } => cast.llvm_type(cx),
336336
PassMode::Indirect { .. } => {
337337
llargument_tys.push(cx.type_ptr());
338338
cx.type_void()
@@ -390,7 +390,9 @@ impl<'ll, 'tcx> FnAbiLlvmExt<'ll, 'tcx> for FnAbi<'tcx, Ty<'tcx>> {
390390
llargument_tys.push(ptr_layout.scalar_pair_element_llvm_type(cx, 1, true));
391391
continue;
392392
}
393-
PassMode::Cast(cast, pad_i32) => {
393+
PassMode::Cast { cast, pad_i32 } => {
394+
// `Cast` means "transmute to `CastType`"; that only makes sense for sized types.
395+
assert!(arg.layout.is_sized());
394396
// add padding
395397
if *pad_i32 {
396398
llargument_tys.push(Reg::i32().llvm_type(cx));
@@ -448,7 +450,7 @@ impl<'ll, 'tcx> FnAbiLlvmExt<'ll, 'tcx> for FnAbi<'tcx, Ty<'tcx>> {
448450
let sret = llvm::CreateStructRetAttr(cx.llcx, self.ret.layout.llvm_type(cx));
449451
attributes::apply_to_llfn(llfn, llvm::AttributePlace::Argument(i), &[sret]);
450452
}
451-
PassMode::Cast(cast, _) => {
453+
PassMode::Cast { cast, pad_i32: _ } => {
452454
cast.attrs.apply_attrs_to_llfn(llvm::AttributePlace::ReturnValue, cx, llfn);
453455
}
454456
_ => {}
@@ -474,7 +476,7 @@ impl<'ll, 'tcx> FnAbiLlvmExt<'ll, 'tcx> for FnAbi<'tcx, Ty<'tcx>> {
474476
apply(a);
475477
apply(b);
476478
}
477-
PassMode::Cast(cast, pad_i32) => {
479+
PassMode::Cast { cast, pad_i32 } => {
478480
if *pad_i32 {
479481
apply(&ArgAttributes::new());
480482
}
@@ -510,7 +512,7 @@ impl<'ll, 'tcx> FnAbiLlvmExt<'ll, 'tcx> for FnAbi<'tcx, Ty<'tcx>> {
510512
let sret = llvm::CreateStructRetAttr(bx.cx.llcx, self.ret.layout.llvm_type(bx));
511513
attributes::apply_to_callsite(callsite, llvm::AttributePlace::Argument(i), &[sret]);
512514
}
513-
PassMode::Cast(cast, _) => {
515+
PassMode::Cast { cast, pad_i32: _ } => {
514516
cast.attrs.apply_attrs_to_callsite(
515517
llvm::AttributePlace::ReturnValue,
516518
&bx.cx,
@@ -553,7 +555,7 @@ impl<'ll, 'tcx> FnAbiLlvmExt<'ll, 'tcx> for FnAbi<'tcx, Ty<'tcx>> {
553555
apply(bx.cx, a);
554556
apply(bx.cx, b);
555557
}
556-
PassMode::Cast(cast, pad_i32) => {
558+
PassMode::Cast { cast, pad_i32 } => {
557559
if *pad_i32 {
558560
apply(bx.cx, &ArgAttributes::new());
559561
}

‎compiler/rustc_codegen_llvm/src/intrinsic.rs

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -165,7 +165,7 @@ impl<'ll, 'tcx> IntrinsicCallMethods<'tcx> for Builder<'_, 'll, 'tcx> {
165165
sym::volatile_load | sym::unaligned_volatile_load => {
166166
let tp_ty = fn_args.type_at(0);
167167
let ptr = args[0].immediate();
168-
let load = if let PassMode::Cast(ty, _) = &fn_abi.ret.mode {
168+
let load = if let PassMode::Cast { cast: ty, pad_i32: _ } = &fn_abi.ret.mode {
169169
let llty = ty.llvm_type(self);
170170
self.volatile_load(llty, ptr)
171171
} else {
@@ -386,7 +386,7 @@ impl<'ll, 'tcx> IntrinsicCallMethods<'tcx> for Builder<'_, 'll, 'tcx> {
386386
};
387387

388388
if !fn_abi.ret.is_ignore() {
389-
if let PassMode::Cast(_, _) = &fn_abi.ret.mode {
389+
if let PassMode::Cast { .. } = &fn_abi.ret.mode {
390390
self.store(llval, result.llval, result.align);
391391
} else {
392392
OperandRef::from_immediate_or_packed_pair(self, llval, result.layout)

‎compiler/rustc_codegen_ssa/src/mir/block.rs

Lines changed: 5 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -416,7 +416,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
416416
}
417417
}
418418

419-
PassMode::Cast(cast_ty, _) => {
419+
PassMode::Cast { cast: cast_ty, pad_i32: _ } => {
420420
let op = match self.locals[mir::RETURN_PLACE] {
421421
LocalRef::Operand(op) => op,
422422
LocalRef::PendingOperand => bug!("use of return before def"),
@@ -1331,7 +1331,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
13311331
) {
13321332
match arg.mode {
13331333
PassMode::Ignore => return,
1334-
PassMode::Cast(_, true) => {
1334+
PassMode::Cast { pad_i32: true, .. } => {
13351335
// Fill padding with undef value, where applicable.
13361336
llargs.push(bx.const_undef(bx.reg_backend_type(&Reg::i32())));
13371337
}
@@ -1368,7 +1368,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
13681368
op.val.store(bx, scratch);
13691369
(scratch.llval, scratch.align, true)
13701370
}
1371-
PassMode::Cast(..) => {
1371+
PassMode::Cast { .. } => {
13721372
let scratch = PlaceRef::alloca(bx, arg.layout);
13731373
op.val.store(bx, scratch);
13741374
(scratch.llval, scratch.align, true)
@@ -1421,7 +1421,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
14211421

14221422
if by_ref && !arg.is_indirect() {
14231423
// Have to load the argument, maybe while casting it.
1424-
if let PassMode::Cast(ty, _) = &arg.mode {
1424+
if let PassMode::Cast { cast: ty, .. } = &arg.mode {
14251425
let llty = bx.cast_backend_type(ty);
14261426
llval = bx.load(llty, llval, align.min(arg.layout.align.abi));
14271427
} else {
@@ -1765,7 +1765,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
17651765
}
17661766
DirectOperand(index) => {
17671767
// If there is a cast, we have to store and reload.
1768-
let op = if let PassMode::Cast(..) = ret_abi.mode {
1768+
let op = if let PassMode::Cast { .. } = ret_abi.mode {
17691769
let tmp = PlaceRef::alloca(bx, ret_abi.layout);
17701770
tmp.storage_live(bx);
17711771
bx.store_arg(&ret_abi, llval, tmp);

‎compiler/rustc_codegen_ssa/src/mir/intrinsic.rs

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -462,7 +462,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
462462
};
463463

464464
if !fn_abi.ret.is_ignore() {
465-
if let PassMode::Cast(..) = &fn_abi.ret.mode {
465+
if let PassMode::Cast { .. } = &fn_abi.ret.mode {
466466
bx.store(llval, result.llval, result.align);
467467
} else {
468468
OperandRef::from_immediate_or_packed_pair(bx, llval, result.layout)

‎compiler/rustc_codegen_ssa/src/mir/mod.rs

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -327,7 +327,7 @@ fn arg_local_refs<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
327327
for i in 0..tupled_arg_tys.len() {
328328
let arg = &fx.fn_abi.args[idx];
329329
idx += 1;
330-
if let PassMode::Cast(_, true) = arg.mode {
330+
if let PassMode::Cast { pad_i32: true, .. } = arg.mode {
331331
llarg_idx += 1;
332332
}
333333
let pr_field = place.project_field(bx, i);
@@ -351,7 +351,7 @@ fn arg_local_refs<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
351351

352352
let arg = &fx.fn_abi.args[idx];
353353
idx += 1;
354-
if let PassMode::Cast(_, true) = arg.mode {
354+
if let PassMode::Cast { pad_i32: true, .. } = arg.mode {
355355
llarg_idx += 1;
356356
}
357357

‎compiler/rustc_target/src/abi/call/mod.rs

Lines changed: 17 additions & 8 deletions
Original file line numberDiff line numberDiff line change
@@ -45,10 +45,9 @@ pub enum PassMode {
4545
///
4646
/// The argument has a layout abi of `ScalarPair`.
4747
Pair(ArgAttributes, ArgAttributes),
48-
/// Pass the argument after casting it, to either a single uniform or a
49-
/// pair of registers. The bool indicates if a `Reg::i32()` dummy argument
50-
/// is emitted before the real argument.
51-
Cast(Box<CastTarget>, bool),
48+
/// Pass the argument after casting it. See the `CastTarget` docs for details. The bool
49+
/// indicates if a `Reg::i32()` dummy argument is emitted before the real argument.
50+
Cast { pad_i32: bool, cast: Box<CastTarget> },
5251
/// Pass the argument indirectly via a hidden pointer.
5352
/// The `extra_attrs` value, if any, is for the extra data (vtable or length)
5453
/// which indicates that it refers to an unsized rvalue.
@@ -64,10 +63,13 @@ impl PassMode {
6463
/// so that needs to be compared as well!
6564
pub fn eq_abi(&self, other: &Self) -> bool {
6665
match (self, other) {
67-
(PassMode::Ignore, PassMode::Ignore) => true, // can still be reached for the return type
66+
(PassMode::Ignore, PassMode::Ignore) => true,
6867
(PassMode::Direct(a1), PassMode::Direct(a2)) => a1.eq_abi(a2),
6968
(PassMode::Pair(a1, b1), PassMode::Pair(a2, b2)) => a1.eq_abi(a2) && b1.eq_abi(b2),
70-
(PassMode::Cast(c1, pad1), PassMode::Cast(c2, pad2)) => c1.eq_abi(c2) && pad1 == pad2,
69+
(
70+
PassMode::Cast { cast: c1, pad_i32: pad1 },
71+
PassMode::Cast { cast: c2, pad_i32: pad2 },
72+
) => c1.eq_abi(c2) && pad1 == pad2,
7173
(
7274
PassMode::Indirect { attrs: a1, extra_attrs: None, on_stack: s1 },
7375
PassMode::Indirect { attrs: a2, extra_attrs: None, on_stack: s2 },
@@ -255,6 +257,13 @@ impl Uniform {
255257
}
256258
}
257259

260+
/// Describes the type used for `PassMode::Cast`.
261+
///
262+
/// Passing arguments in this mode works as follows: the registers in the `prefix` (the ones that
263+
/// are `Some`) get laid out one after the other (using `repr(C)` layout rules). Then the
264+
/// `rest.unit` register type gets repeated often enough to cover `rest.size`. This describes the
265+
/// actual type used for the call; the Rust type of the argument is then transmuted to this ABI type
266+
/// (and all data in the padding between the registers is dropped).
258267
#[derive(Clone, PartialEq, Eq, Hash, Debug, HashStable_Generic)]
259268
pub struct CastTarget {
260269
pub prefix: [Option<Reg>; 8],
@@ -602,11 +611,11 @@ impl<'a, Ty> ArgAbi<'a, Ty> {
602611
}
603612

604613
pub fn cast_to<T: Into<CastTarget>>(&mut self, target: T) {
605-
self.mode = PassMode::Cast(Box::new(target.into()), false);
614+
self.mode = PassMode::Cast { cast: Box::new(target.into()), pad_i32: false };
606615
}
607616

608617
pub fn cast_to_and_pad_i32<T: Into<CastTarget>>(&mut self, target: T, pad_i32: bool) {
609-
self.mode = PassMode::Cast(Box::new(target.into()), pad_i32);
618+
self.mode = PassMode::Cast { cast: Box::new(target.into()), pad_i32 };
610619
}
611620

612621
pub fn is_indirect(&self) -> bool {

‎compiler/rustc_target/src/abi/call/x86.rs

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -148,7 +148,7 @@ where
148148
PassMode::Direct(ref mut attrs) => attrs,
149149
PassMode::Pair(..)
150150
| PassMode::Indirect { attrs: _, extra_attrs: Some(_), on_stack: _ }
151-
| PassMode::Cast(..) => {
151+
| PassMode::Cast { .. } => {
152152
unreachable!("x86 shouldn't be passing arguments by {:?}", arg.mode)
153153
}
154154
};

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