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Simplify some mir passes by using let chains #116549

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Oct 9, 2023
Merged

Simplify some mir passes by using let chains #116549

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25 changes: 5 additions & 20 deletions compiler/rustc_mir_transform/src/lower_intrinsics.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2,9 +2,8 @@

use crate::MirPass;
use rustc_middle::mir::*;
use rustc_middle::ty::GenericArgsRef;
use rustc_middle::ty::{self, Ty, TyCtxt};
use rustc_span::symbol::{sym, Symbol};
use rustc_middle::ty::{self, TyCtxt};
use rustc_span::symbol::sym;
use rustc_target::abi::{FieldIdx, VariantIdx};

pub struct LowerIntrinsics;
Expand All @@ -16,12 +15,10 @@ impl<'tcx> MirPass<'tcx> for LowerIntrinsics {
let terminator = block.terminator.as_mut().unwrap();
if let TerminatorKind::Call { func, args, destination, target, .. } =
&mut terminator.kind
&& let ty::FnDef(def_id, generic_args) = *func.ty(local_decls, tcx).kind()
&& tcx.is_intrinsic(def_id)
{
let func_ty = func.ty(local_decls, tcx);
let Some((intrinsic_name, generic_args)) = resolve_rust_intrinsic(tcx, func_ty)
else {
continue;
};
let intrinsic_name = tcx.item_name(def_id);
match intrinsic_name {
sym::unreachable => {
terminator.kind = TerminatorKind::Unreachable;
Expand Down Expand Up @@ -309,15 +306,3 @@ impl<'tcx> MirPass<'tcx> for LowerIntrinsics {
}
}
}

fn resolve_rust_intrinsic<'tcx>(
tcx: TyCtxt<'tcx>,
func_ty: Ty<'tcx>,
) -> Option<(Symbol, GenericArgsRef<'tcx>)> {
if let ty::FnDef(def_id, args) = *func_ty.kind() {
if tcx.is_intrinsic(def_id) {
return Some((tcx.item_name(def_id), args));
}
}
None
}
79 changes: 28 additions & 51 deletions compiler/rustc_mir_transform/src/lower_slice_len.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -34,67 +34,44 @@ pub fn lower_slice_len_calls<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
}
}

struct SliceLenPatchInformation<'tcx> {
add_statement: Statement<'tcx>,
new_terminator_kind: TerminatorKind<'tcx>,
}

fn lower_slice_len_call<'tcx>(
tcx: TyCtxt<'tcx>,
block: &mut BasicBlockData<'tcx>,
local_decls: &IndexSlice<Local, LocalDecl<'tcx>>,
slice_len_fn_item_def_id: DefId,
) {
let mut patch_found: Option<SliceLenPatchInformation<'_>> = None;

let terminator = block.terminator();
match &terminator.kind {
TerminatorKind::Call {
func,
args,
destination,
target: Some(bb),
call_source: CallSource::Normal,
..
} => {
// some heuristics for fast rejection
if args.len() != 1 {
return;
}
let Some(arg) = args[0].place() else { return };
let func_ty = func.ty(local_decls, tcx);
match func_ty.kind() {
ty::FnDef(fn_def_id, _) if fn_def_id == &slice_len_fn_item_def_id => {
// perform modifications
// from something like `_5 = core::slice::<impl [u8]>::len(move _6) -> bb1`
// into:
// ```
// _5 = Len(*_6)
// goto bb1
// ```
if let TerminatorKind::Call {
func,
args,
destination,
target: Some(bb),
call_source: CallSource::Normal,
..
} = &terminator.kind
// some heuristics for fast rejection
&& let [arg] = &args[..]
&& let Some(arg) = arg.place()
&& let ty::FnDef(fn_def_id, _) = func.ty(local_decls, tcx).kind()
&& *fn_def_id == slice_len_fn_item_def_id
{
// perform modifications from something like:
// _5 = core::slice::<impl [u8]>::len(move _6) -> bb1
// into:
// _5 = Len(*_6)
// goto bb1

// make new RValue for Len
let deref_arg = tcx.mk_place_deref(arg);
let r_value = Rvalue::Len(deref_arg);
let len_statement_kind =
StatementKind::Assign(Box::new((*destination, r_value)));
let add_statement =
Statement { kind: len_statement_kind, source_info: terminator.source_info };
// make new RValue for Len
let deref_arg = tcx.mk_place_deref(arg);
let r_value = Rvalue::Len(deref_arg);
let len_statement_kind =
StatementKind::Assign(Box::new((*destination, r_value)));
let add_statement =
Statement { kind: len_statement_kind, source_info: terminator.source_info };

// modify terminator into simple Goto
let new_terminator_kind = TerminatorKind::Goto { target: *bb };

let patch = SliceLenPatchInformation { add_statement, new_terminator_kind };

patch_found = Some(patch);
}
_ => {}
}
}
_ => {}
}
// modify terminator into simple Goto
let new_terminator_kind = TerminatorKind::Goto { target: *bb };

if let Some(SliceLenPatchInformation { add_statement, new_terminator_kind }) = patch_found {
block.statements.push(add_statement);
block.terminator_mut().kind = new_terminator_kind;
}
Expand Down
25 changes: 10 additions & 15 deletions compiler/rustc_mir_transform/src/uninhabited_enum_branching.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -30,22 +30,17 @@ fn get_switched_on_type<'tcx>(
let terminator = block_data.terminator();

// Only bother checking blocks which terminate by switching on a local.
if let Some(local) = get_discriminant_local(&terminator.kind) {
let stmt_before_term = (!block_data.statements.is_empty())
.then(|| &block_data.statements[block_data.statements.len() - 1].kind);

if let Some(StatementKind::Assign(box (l, Rvalue::Discriminant(place)))) = stmt_before_term
{
if l.as_local() == Some(local) {
let ty = place.ty(body, tcx).ty;
if ty.is_enum() {
return Some(ty);
}
}
}
if let Some(local) = get_discriminant_local(&terminator.kind)
&& let [.., stmt_before_term] = &block_data.statements[..]
&& let StatementKind::Assign(box (l, Rvalue::Discriminant(place))) = stmt_before_term.kind
&& l.as_local() == Some(local)
&& let ty = place.ty(body, tcx).ty
&& ty.is_enum()
{
Some(ty)
} else {
None
}

None
}

fn variant_discriminants<'tcx>(
Expand Down
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