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Sync discriminant getter and setter with upstream

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Fixes #683
This commit is contained in:
bjorn3 2019-08-26 11:03:06 +02:00
parent f6c39fa701
commit e704eb5259
2 changed files with 138 additions and 54 deletions
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69
example/mini_core_hello_world.rs
View file

@ -264,4 +264,73 @@ fn main() {
static ANOTHER_STATIC: &u8 = &A_STATIC;
assert_eq!(*ANOTHER_STATIC, 42);
check_niche_behavior();
}
// Copied ui/issues/issue-61696.rs
pub enum Infallible {}
// The check that the `bool` field of `V1` is encoding a "niche variant"
// (i.e. not `V1`, so `V3` or `V4`) used to be mathematically incorrect,
// causing valid `V1` values to be interpreted as other variants.
pub enum E1 {
V1 { f: bool },
V2 { f: Infallible },
V3,
V4,
}
// Computing the discriminant used to be done using the niche type (here `u8`,
// from the `bool` field of `V1`), overflowing for variants with large enough
// indices (`V3` and `V4`), causing them to be interpreted as other variants.
pub enum E2<X> {
V1 { f: bool },
/*_00*/ _01(X), _02(X), _03(X), _04(X), _05(X), _06(X), _07(X),
_08(X), _09(X), _0A(X), _0B(X), _0C(X), _0D(X), _0E(X), _0F(X),
_10(X), _11(X), _12(X), _13(X), _14(X), _15(X), _16(X), _17(X),
_18(X), _19(X), _1A(X), _1B(X), _1C(X), _1D(X), _1E(X), _1F(X),
_20(X), _21(X), _22(X), _23(X), _24(X), _25(X), _26(X), _27(X),
_28(X), _29(X), _2A(X), _2B(X), _2C(X), _2D(X), _2E(X), _2F(X),
_30(X), _31(X), _32(X), _33(X), _34(X), _35(X), _36(X), _37(X),
_38(X), _39(X), _3A(X), _3B(X), _3C(X), _3D(X), _3E(X), _3F(X),
_40(X), _41(X), _42(X), _43(X), _44(X), _45(X), _46(X), _47(X),
_48(X), _49(X), _4A(X), _4B(X), _4C(X), _4D(X), _4E(X), _4F(X),
_50(X), _51(X), _52(X), _53(X), _54(X), _55(X), _56(X), _57(X),
_58(X), _59(X), _5A(X), _5B(X), _5C(X), _5D(X), _5E(X), _5F(X),
_60(X), _61(X), _62(X), _63(X), _64(X), _65(X), _66(X), _67(X),
_68(X), _69(X), _6A(X), _6B(X), _6C(X), _6D(X), _6E(X), _6F(X),
_70(X), _71(X), _72(X), _73(X), _74(X), _75(X), _76(X), _77(X),
_78(X), _79(X), _7A(X), _7B(X), _7C(X), _7D(X), _7E(X), _7F(X),
_80(X), _81(X), _82(X), _83(X), _84(X), _85(X), _86(X), _87(X),
_88(X), _89(X), _8A(X), _8B(X), _8C(X), _8D(X), _8E(X), _8F(X),
_90(X), _91(X), _92(X), _93(X), _94(X), _95(X), _96(X), _97(X),
_98(X), _99(X), _9A(X), _9B(X), _9C(X), _9D(X), _9E(X), _9F(X),
_A0(X), _A1(X), _A2(X), _A3(X), _A4(X), _A5(X), _A6(X), _A7(X),
_A8(X), _A9(X), _AA(X), _AB(X), _AC(X), _AD(X), _AE(X), _AF(X),
_B0(X), _B1(X), _B2(X), _B3(X), _B4(X), _B5(X), _B6(X), _B7(X),
_B8(X), _B9(X), _BA(X), _BB(X), _BC(X), _BD(X), _BE(X), _BF(X),
_C0(X), _C1(X), _C2(X), _C3(X), _C4(X), _C5(X), _C6(X), _C7(X),
_C8(X), _C9(X), _CA(X), _CB(X), _CC(X), _CD(X), _CE(X), _CF(X),
_D0(X), _D1(X), _D2(X), _D3(X), _D4(X), _D5(X), _D6(X), _D7(X),
_D8(X), _D9(X), _DA(X), _DB(X), _DC(X), _DD(X), _DE(X), _DF(X),
_E0(X), _E1(X), _E2(X), _E3(X), _E4(X), _E5(X), _E6(X), _E7(X),
_E8(X), _E9(X), _EA(X), _EB(X), _EC(X), _ED(X), _EE(X), _EF(X),
_F0(X), _F1(X), _F2(X), _F3(X), _F4(X), _F5(X), _F6(X), _F7(X),
_F8(X), _F9(X), _FA(X), _FB(X), _FC(X), _FD(X), _FE(X), _FF(X),
V3,
V4,
}
fn check_niche_behavior () {
if let E1::V2 { .. } = (E1::V1 { f: true }) {
unsafe { intrinsics::abort(); }
}
if let E2::V1 { .. } = E2::V3::<Infallible> {
unsafe { intrinsics::abort(); }
}
}

123
src/discriminant.rs
View file

@ -1,3 +1,5 @@
//! Adapted from https://github.com/rust-lang/rust/blob/d760df5aea483aae041c9a241e7acacf48f75035/src/librustc_codegen_ssa/mir/place.rs
use crate::prelude::*;
pub fn codegen_set_discriminant<'tcx>(
@ -6,7 +8,7 @@ pub fn codegen_set_discriminant<'tcx>(
variant_index: VariantIdx,
) {
let layout = place.layout();
if layout.for_variant(&*fx, variant_index).abi == layout::Abi::Uninhabited {
if layout.for_variant(fx, variant_index).abi.is_uninhabited() {
return;
}
match layout.variants {
@ -40,16 +42,9 @@ pub fn codegen_set_discriminant<'tcx>(
} => {
if variant_index != dataful_variant {
let niche = place.place_field(fx, mir::Field::new(discr_index));
//let niche_llty = niche.layout.immediate_llvm_type(bx.cx);
let niche_value =
((variant_index.as_u32() - niche_variants.start().as_u32()) as u128)
.wrapping_add(niche_start);
// FIXME(eddyb) Check the actual primitive type here.
let niche_llval = if niche_value == 0 {
CValue::const_val(fx, niche.layout().ty, 0)
} else {
CValue::const_val(fx, niche.layout().ty, niche_value)
};
let niche_value = variant_index.as_u32() - niche_variants.start().as_u32();
let niche_value = u128::from(niche_value).wrapping_add(niche_start);
let niche_llval = CValue::const_val(fx, niche.layout().ty, niche_value);
niche.write_cvalue(fx, niche_llval);
}
}
@ -71,10 +66,8 @@ pub fn codegen_get_discriminant<'tcx>(
layout::Variants::Single { index } => {
let discr_val = layout
.ty
.ty_adt_def()
.map_or(u128::from(index.as_u32()), |def| {
def.discriminant_for_variant(fx.tcx, *index).val
});
.discriminant_for_variant(fx.tcx, *index)
.map_or(u128::from(index.as_u32()), |discr| discr.val);
return CValue::const_val(fx, dest_layout.ty, discr_val);
}
layout::Variants::Multiple { discr, discr_index, discr_kind, variants: _ } => {
@ -82,16 +75,20 @@ pub fn codegen_get_discriminant<'tcx>(
}
};
let discr = value.value_field(fx, mir::Field::new(discr_index));
let discr_ty = discr.layout().ty;
let lldiscr = discr.load_scalar(fx);
match discr_kind {
let cast_to = fx.clif_type(dest_layout.ty).unwrap();
// Read the tag/niche-encoded discriminant from memory.
let encoded_discr = value.value_field(fx, mir::Field::new(discr_index));
let encoded_discr = encoded_discr.load_scalar(fx);
// Decode the discriminant (specifically if it's niche-encoded).
match *discr_kind {
layout::DiscriminantKind::Tag => {
let signed = match discr_scalar.value {
layout::Int(_, signed) => signed,
_ => false,
_ => false
};
let val = clif_intcast(fx, lldiscr, fx.clif_type(dest_layout.ty).unwrap(), signed);
let val = clif_intcast(fx, encoded_discr, cast_to, signed);
return CValue::by_val(val, dest_layout);
}
layout::DiscriminantKind::Niche {
@ -99,40 +96,58 @@ pub fn codegen_get_discriminant<'tcx>(
ref niche_variants,
niche_start,
} => {
let niche_llty = fx.clif_type(discr_ty).unwrap();
let dest_clif_ty = fx.clif_type(dest_layout.ty).unwrap();
if niche_variants.start() == niche_variants.end() {
let b = codegen_icmp_imm(fx, IntCC::Equal, lldiscr, *niche_start as i128);
let if_true = fx
.bcx
.ins()
.iconst(dest_clif_ty, niche_variants.start().as_u32() as i64);
let if_false = fx
.bcx
.ins()
.iconst(dest_clif_ty, dataful_variant.as_u32() as i64);
let val = fx.bcx.ins().select(b, if_true, if_false);
return CValue::by_val(val, dest_layout);
// Rebase from niche values to discriminants, and check
// whether the result is in range for the niche variants.
// We first compute the "relative discriminant" (wrt `niche_variants`),
// that is, if `n = niche_variants.end() - niche_variants.start()`,
// we remap `niche_start..=niche_start + n` (which may wrap around)
// to (non-wrap-around) `0..=n`, to be able to check whether the
// discriminant corresponds to a niche variant with one comparison.
// We also can't go directly to the (variant index) discriminant
// and check that it is in the range `niche_variants`, because
// that might not fit in the same type, on top of needing an extra
// comparison (see also the comment on `let niche_discr`).
let relative_discr = if niche_start == 0 {
encoded_discr
} else {
// Rebase from niche values to discriminant values.
let delta = niche_start.wrapping_sub(niche_variants.start().as_u32() as u128);
let delta = fx.bcx.ins().iconst(niche_llty, delta as u64 as i64);
let lldiscr = fx.bcx.ins().isub(lldiscr, delta);
let b = codegen_icmp_imm(
fx,
IntCC::UnsignedLessThanOrEqual,
lldiscr,
i128::from(niche_variants.end().as_u32()),
);
let if_true =
clif_intcast(fx, lldiscr, fx.clif_type(dest_layout.ty).unwrap(), false);
let if_false = fx
.bcx
.ins()
.iconst(dest_clif_ty, dataful_variant.as_u32() as i64);
let val = fx.bcx.ins().select(b, if_true, if_false);
return CValue::by_val(val, dest_layout);
}
// FIXME handle niche_start > i64::max_value()
fx.bcx.ins().iadd_imm(encoded_discr, -i64::try_from(niche_start).unwrap())
};
let relative_max = niche_variants.end().as_u32() - niche_variants.start().as_u32();
let is_niche = {
codegen_icmp_imm(fx, IntCC::UnsignedLessThanOrEqual, relative_discr, i128::from(relative_max))
};
// NOTE(eddyb) this addition needs to be performed on the final
// type, in case the niche itself can't represent all variant
// indices (e.g. `u8` niche with more than `256` variants,
// but enough uninhabited variants so that the remaining variants
// fit in the niche).
// In other words, `niche_variants.end - niche_variants.start`
// is representable in the niche, but `niche_variants.end`
// might not be, in extreme cases.
let niche_discr = {
let relative_discr = if relative_max == 0 {
// HACK(eddyb) since we have only one niche, we know which
// one it is, and we can avoid having a dynamic value here.
fx.bcx.ins().iconst(cast_to, 0)
} else {
clif_intcast(fx, relative_discr, cast_to, false)
};
fx.bcx.ins().iadd_imm(
relative_discr,
i64::from(niche_variants.start().as_u32()),
)
};
let dataful_variant = fx.bcx.ins().iconst(cast_to, i64::from(dataful_variant.as_u32()));
let discr = fx.bcx.ins().select(
is_niche,
niche_discr,
dataful_variant,
);
CValue::by_val(discr, dest_layout)
}
}
}