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rustc_codegen_ssa: fix range check in codegen_get_discr.
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@eddyb
eddyb committed Jul 12, 2019
1 parent e60c7ed commit c063057
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Showing 2 changed files with 111 additions and 23 deletions.
70 changes: 47 additions & 23 deletions src/librustc_codegen_ssa/mir/place.rs
View file
Expand Up @@ -250,37 +250,61 @@ impl<'a, 'tcx, V: CodegenObject> PlaceRef<'tcx, V> {
ref niche_variants,
niche_start,
} => {
// Rebase from niche values to discriminants, and check
// whether the result is in range for the niche variants.
let niche_llty = bx.cx().immediate_backend_type(encoded_discr.layout);
let encoded_discr = encoded_discr.immediate();
let (is_niche, niche_discr) = if niche_variants.start() == niche_variants.end() {
// Special case for when we can use a simple equality check,
// which covers null pointers, and needs simpler codegen.
// FIXME(eddyb): check the actual primitive type here.
let encoded_niche = if niche_start == 0 {
// HACK(eddyb): using `c_null` as it works on all types.

// 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 {
// Avoid subtracting `0`, which wouldn't work for pointers.
// FIXME(eddyb) check the actual primitive type here.
encoded_discr
} else {
bx.sub(encoded_discr, bx.cx().const_uint_big(niche_llty, niche_start))
};
let relative_max = niche_variants.end().as_u32() - niche_variants.start().as_u32();
let is_niche = {
let relative_max = if relative_max == 0 {
// Avoid calling `const_uint`, which wouldn't work for pointers.
// FIXME(eddyb) check the actual primitive type here.
bx.cx().const_null(niche_llty)
} else {
bx.cx().const_uint_big(niche_llty, niche_start)
bx.cx().const_uint(niche_llty, relative_max as u64)
};
bx.icmp(IntPredicate::IntULE, relative_discr, 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.
bx.cx().const_uint(cast_to, 0)
} else {
bx.intcast(relative_discr, cast_to, false)
};
(
bx.icmp(IntPredicate::IntEQ, encoded_discr, encoded_niche),
bx.add(
relative_discr,
bx.cx().const_uint(cast_to, niche_variants.start().as_u32() as u64),
)
} else {
// Rebase from niche values to discriminants, and check
// whether the result is in range for the niche variants.
// FIXME(#61696) the range check is sometimes incorrect.
let delta = niche_start.wrapping_sub(niche_variants.start().as_u32() as u128);
let niche_discr =
bx.sub(encoded_discr, bx.cx().const_uint_big(niche_llty, delta));
let niche_discr_max =
bx.cx().const_uint(niche_llty, niche_variants.end().as_u32() as u64);
(
bx.icmp(IntPredicate::IntULE, niche_discr, niche_discr_max),
niche_discr,
)
};
let niche_discr = bx.intcast(niche_discr, cast_to, false);

bx.select(
is_niche,
niche_discr,
Expand Down
64 changes: 64 additions & 0 deletions src/test/run-pass/issues/issue-61696.rs
View file
@@ -0,0 +1,64 @@
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 main() {
if let E1::V2 { .. } = (E1::V1 { f: true }) {
unreachable!()
}

if let E2::V1 { .. } = E2::V3::<Infallible> {
unreachable!()
}
}

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