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Auto merge of #96862 - oli-obk:enum_cast_mir, r=RalfJung

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Change enum->int casts to not go through MIR casts.

follow-up to https://github.com/rust-lang/rust/pull/96814

this simplifies all backends and even gives LLVM more information about the return value of `Rvalue::Discriminant`, enabling optimizations in more cases.
This commit is contained in:
bors 2022-07-05 09:36:29 +00:00
commit 53792b9c5c
21 changed files with 238 additions and 143 deletions
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25
compiler/rustc_const_eval/src/interpret/cast.rs
View file

@ -8,7 +8,7 @@ use rustc_middle::mir::CastKind;
use rustc_middle::ty::adjustment::PointerCast;
use rustc_middle::ty::layout::{IntegerExt, LayoutOf, TyAndLayout};
use rustc_middle::ty::{self, FloatTy, Ty, TypeAndMut};
use rustc_target::abi::{Integer, Variants};
use rustc_target::abi::Integer;
use rustc_type_ir::sty::TyKind::*;
use super::{
@ -128,12 +128,10 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
Float(FloatTy::F64) => {
return Ok(self.cast_from_float(src.to_scalar()?.to_f64()?, cast_ty).into());
}
// The rest is integer/pointer-"like", including fn ptr casts and casts from enums that
// are represented as integers.
// The rest is integer/pointer-"like", including fn ptr casts
_ => assert!(
src.layout.ty.is_bool()
|| src.layout.ty.is_char()
|| src.layout.ty.is_enum()
|| src.layout.ty.is_integral()
|| src.layout.ty.is_any_ptr(),
"Unexpected cast from type {:?}",
@ -143,25 +141,6 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
// # First handle non-scalar source values.
// Handle cast from a ZST enum (0 or 1 variants).
match src.layout.variants {
Variants::Single { index } => {
if src.layout.abi.is_uninhabited() {
// This is dead code, because an uninhabited enum is UB to
// instantiate.
throw_ub!(Unreachable);
}
if let Some(discr) = src.layout.ty.discriminant_for_variant(*self.tcx, index) {
assert!(src.layout.is_zst());
let discr_layout = self.layout_of(discr.ty)?;
let scalar = Scalar::from_uint(discr.val, discr_layout.layout.size());
return Ok(self.cast_from_int_like(scalar, discr_layout, cast_ty)?.into());
}
}
Variants::Multiple { .. } => {}
}
// Handle casting any ptr to raw ptr (might be a fat ptr).
if src.layout.ty.is_any_ptr() && cast_ty.is_unsafe_ptr() {
let dest_layout = self.layout_of(cast_ty)?;

32
compiler/rustc_const_eval/src/transform/validate.rs
View file

@ -7,9 +7,9 @@ use rustc_middle::mir::interpret::Scalar;
use rustc_middle::mir::visit::NonUseContext::VarDebugInfo;
use rustc_middle::mir::visit::{PlaceContext, Visitor};
use rustc_middle::mir::{
traversal, AggregateKind, BasicBlock, BinOp, Body, BorrowKind, Local, Location, MirPass,
MirPhase, Operand, Place, PlaceElem, PlaceRef, ProjectionElem, Rvalue, SourceScope, Statement,
StatementKind, Terminator, TerminatorKind, UnOp, START_BLOCK,
traversal, AggregateKind, BasicBlock, BinOp, Body, BorrowKind, CastKind, Local, Location,
MirPass, MirPhase, Operand, Place, PlaceElem, PlaceRef, ProjectionElem, Rvalue, SourceScope,
Statement, StatementKind, Terminator, TerminatorKind, UnOp, START_BLOCK,
};
use rustc_middle::ty::fold::BottomUpFolder;
use rustc_middle::ty::{self, InstanceDef, ParamEnv, Ty, TyCtxt, TypeFoldable};
@ -361,6 +361,7 @@ impl<'a, 'tcx> Visitor<'tcx> for TypeChecker<'a, 'tcx> {
);
}
}
Rvalue::Ref(..) => {}
Rvalue::Len(p) => {
let pty = p.ty(&self.body.local_decls, self.tcx).ty;
check_kinds!(
@ -503,7 +504,30 @@ impl<'a, 'tcx> Visitor<'tcx> for TypeChecker<'a, 'tcx> {
let a = operand.ty(&self.body.local_decls, self.tcx);
check_kinds!(a, "Cannot shallow init type {:?}", ty::RawPtr(..));
}
_ => {}
Rvalue::Cast(kind, operand, target_type) => {
match kind {
CastKind::Misc => {
let op_ty = operand.ty(self.body, self.tcx);
if op_ty.is_enum() {
self.fail(
location,
format!(
"enum -> int casts should go through `Rvalue::Discriminant`: {operand:?}:{op_ty} as {target_type}",
),
);
}
}
// Nothing to check here
CastKind::PointerFromExposedAddress
| CastKind::PointerExposeAddress
| CastKind::Pointer(_) => {}
}
}
Rvalue::Repeat(_, _)
| Rvalue::ThreadLocalRef(_)
| Rvalue::AddressOf(_, _)
| Rvalue::NullaryOp(_, _)
| Rvalue::Discriminant(_) => {}
}
self.super_rvalue(rvalue, location);
}