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tmiaskotmiasko
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Lower intrinsics calls: forget, size_of, unreachable, wrapping_*
This allows constant propagation to evaluate `size_of` and `wrapping_*`, and unreachable propagation to propagate a call to `unreachable`. The lowering is performed as a MIR optimization, rather than during MIR building to preserve the special status of intrinsics with respect to unsafety checks and promotion.
1 parent 30e49a9 commit 6903273

10 files changed

+373
-5
lines changed

‎compiler/rustc_mir/src/transform/lower_intrinsics.rs

+108
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,108 @@
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//! Lowers intrinsic calls
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use crate::transform::MirPass;
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use rustc_middle::mir::*;
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use rustc_middle::ty::subst::SubstsRef;
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use rustc_middle::ty::{self, Ty, TyCtxt};
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use rustc_span::symbol::{sym, Symbol};
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use rustc_target::spec::abi::Abi;
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pub struct LowerIntrinsics;
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impl<'tcx> MirPass<'tcx> for LowerIntrinsics {
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fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
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for block in body.basic_blocks_mut() {
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let terminator = block.terminator.as_mut().unwrap();
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if let TerminatorKind::Call {
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func: Operand::Constant(box Constant { literal: ty::Const { ty: func_ty, .. }, .. }),
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args,
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destination,
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..
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} = &mut terminator.kind
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{
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let (intrinsic_name, substs) = match resolve_rust_intrinsic(tcx, func_ty) {
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None => continue,
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Some(it) => it,
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};
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match intrinsic_name {
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sym::unreachable => {
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terminator.kind = TerminatorKind::Unreachable;
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}
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sym::forget => {
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if let Some((destination, target)) = *destination {
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block.statements.push(Statement {
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source_info: terminator.source_info,
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kind: StatementKind::Assign(box (
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destination,
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Rvalue::Use(Operand::Constant(box Constant {
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span: terminator.source_info.span,
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user_ty: None,
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literal: ty::Const::zero_sized(tcx, tcx.types.unit),
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})),
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)),
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});
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terminator.kind = TerminatorKind::Goto { target };
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}
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}
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sym::wrapping_add | sym::wrapping_sub | sym::wrapping_mul => {
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if let Some((destination, target)) = *destination {
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let lhs;
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let rhs;
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{
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let mut args = args.drain(..);
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lhs = args.next().unwrap();
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rhs = args.next().unwrap();
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}
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let bin_op = match intrinsic_name {
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sym::wrapping_add => BinOp::Add,
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sym::wrapping_sub => BinOp::Sub,
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sym::wrapping_mul => BinOp::Mul,
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_ => bug!("unexpected intrinsic"),
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};
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block.statements.push(Statement {
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source_info: terminator.source_info,
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kind: StatementKind::Assign(box (
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destination,
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Rvalue::BinaryOp(bin_op, lhs, rhs),
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)),
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});
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terminator.kind = TerminatorKind::Goto { target };
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}
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}
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sym::add_with_overflow | sym::sub_with_overflow | sym::mul_with_overflow => {
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// The checked binary operations are not suitable target for lowering here,
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// since their semantics depend on the value of overflow-checks flag used
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// during codegen. Issue #35310.
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}
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sym::size_of => {
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if let Some((destination, target)) = *destination {
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let tp_ty = substs.type_at(0);
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block.statements.push(Statement {
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source_info: terminator.source_info,
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kind: StatementKind::Assign(box (
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destination,
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Rvalue::NullaryOp(NullOp::SizeOf, tp_ty),
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)),
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});
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terminator.kind = TerminatorKind::Goto { target };
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}
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}
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_ => {}
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}
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}
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}
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}
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}
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fn resolve_rust_intrinsic(
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tcx: TyCtxt<'tcx>,
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func_ty: Ty<'tcx>,
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) -> Option<(Symbol, SubstsRef<'tcx>)> {
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if let ty::FnDef(def_id, substs) = *func_ty.kind() {
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let fn_sig = func_ty.fn_sig(tcx);
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if fn_sig.abi() == Abi::RustIntrinsic {
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return Some((tcx.item_name(def_id), substs));
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}
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}
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None
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}

‎compiler/rustc_mir/src/transform/mod.rs

+2
Original file line numberDiff line numberDiff line change
@@ -32,6 +32,7 @@ pub mod function_item_references;
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pub mod generator;
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pub mod inline;
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pub mod instcombine;
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pub mod lower_intrinsics;
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pub mod match_branches;
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pub mod multiple_return_terminators;
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pub mod no_landing_pads;
@@ -390,6 +391,7 @@ fn run_optimization_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
390391

391392
// The main optimizations that we do on MIR.
392393
let optimizations: &[&dyn MirPass<'tcx>] = &[
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&lower_intrinsics::LowerIntrinsics,
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&remove_unneeded_drops::RemoveUnneededDrops,
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&match_branches::MatchBranchSimplification,
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// inst combine is after MatchBranchSimplification to clean up Ne(_1, false)

‎src/test/mir-opt/lower_intrinsics.f_u64.PreCodegen.before.mir

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// MIR for `f_u64` before PreCodegen
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fn f_u64() -> () {
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let mut _0: (); // return place in scope 0 at $DIR/lower_intrinsics.rs:34:16: 34:16
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scope 1 (inlined f_dispatch::<u64>) { // at $DIR/lower_intrinsics.rs:35:5: 35:21
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debug t => _2; // in scope 1 at $DIR/lower_intrinsics.rs:35:5: 35:21
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let _1: (); // in scope 1 at $DIR/lower_intrinsics.rs:35:5: 35:21
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let mut _2: u64; // in scope 1 at $DIR/lower_intrinsics.rs:35:5: 35:21
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scope 2 (inlined std::mem::size_of::<u64>) { // at $DIR/lower_intrinsics.rs:35:5: 35:21
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}
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}
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bb0: {
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_2 = const 0_u64; // scope 0 at $DIR/lower_intrinsics.rs:35:5: 35:21
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StorageLive(_1); // scope 1 at $DIR/lower_intrinsics.rs:35:5: 35:21
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_1 = f_non_zst::<u64>(move _2) -> bb1; // scope 1 at $DIR/lower_intrinsics.rs:35:5: 35:21
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// mir::Constant
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// + span: $DIR/lower_intrinsics.rs:35:5: 35:21
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// + literal: Const { ty: fn(u64) {f_non_zst::<u64>}, val: Value(Scalar(<ZST>)) }
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}
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bb1: {
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StorageDead(_1); // scope 1 at $DIR/lower_intrinsics.rs:35:5: 35:21
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_0 = const (); // scope 0 at $DIR/lower_intrinsics.rs:34:16: 36:2
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return; // scope 0 at $DIR/lower_intrinsics.rs:36:2: 36:2
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}
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}

‎src/test/mir-opt/lower_intrinsics.f_unit.PreCodegen.before.mir

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// MIR for `f_unit` before PreCodegen
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fn f_unit() -> () {
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let mut _0: (); // return place in scope 0 at $DIR/lower_intrinsics.rs:28:17: 28:17
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let mut _1: (); // in scope 0 at $DIR/lower_intrinsics.rs:29:16: 29:18
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scope 1 (inlined f_dispatch::<()>) { // at $DIR/lower_intrinsics.rs:29:5: 29:19
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debug t => _1; // in scope 1 at $DIR/lower_intrinsics.rs:29:5: 29:19
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let _2: (); // in scope 1 at $DIR/lower_intrinsics.rs:29:5: 29:19
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scope 2 (inlined std::mem::size_of::<()>) { // at $DIR/lower_intrinsics.rs:29:5: 29:19
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}
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}
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bb0: {
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StorageLive(_1); // scope 0 at $DIR/lower_intrinsics.rs:29:16: 29:18
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StorageLive(_2); // scope 1 at $DIR/lower_intrinsics.rs:29:5: 29:19
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_2 = f_zst::<()>(const ()) -> bb1; // scope 1 at $DIR/lower_intrinsics.rs:29:5: 29:19
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// mir::Constant
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// + span: $DIR/lower_intrinsics.rs:29:5: 29:19
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// + literal: Const { ty: fn(()) {f_zst::<()>}, val: Value(Scalar(<ZST>)) }
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}
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bb1: {
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StorageDead(_2); // scope 1 at $DIR/lower_intrinsics.rs:29:5: 29:19
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StorageDead(_1); // scope 0 at $DIR/lower_intrinsics.rs:29:18: 29:19
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_0 = const (); // scope 0 at $DIR/lower_intrinsics.rs:28:17: 30:2
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return; // scope 0 at $DIR/lower_intrinsics.rs:30:2: 30:2
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}
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}

‎src/test/mir-opt/lower_intrinsics.forget.LowerIntrinsics.diff

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- // MIR for `forget` before LowerIntrinsics
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+ // MIR for `forget` after LowerIntrinsics
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fn forget(_1: T) -> () {
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debug t => _1; // in scope 0 at $DIR/lower_intrinsics.rs:18:18: 18:19
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let mut _0: (); // return place in scope 0 at $DIR/lower_intrinsics.rs:18:24: 18:24
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let _2: (); // in scope 0 at $DIR/lower_intrinsics.rs:19:14: 19:41
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let mut _3: T; // in scope 0 at $DIR/lower_intrinsics.rs:19:39: 19:40
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scope 1 {
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}
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bb0: {
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StorageLive(_2); // scope 0 at $DIR/lower_intrinsics.rs:19:5: 19:43
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StorageLive(_3); // scope 1 at $DIR/lower_intrinsics.rs:19:39: 19:40
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_3 = move _1; // scope 1 at $DIR/lower_intrinsics.rs:19:39: 19:40
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- _2 = std::intrinsics::forget::<T>(move _3) -> bb1; // scope 1 at $DIR/lower_intrinsics.rs:19:14: 19:41
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- // mir::Constant
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- // + span: $DIR/lower_intrinsics.rs:19:14: 19:38
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- // + literal: Const { ty: unsafe extern "rust-intrinsic" fn(T) {std::intrinsics::forget::<T>}, val: Value(Scalar(<ZST>)) }
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+ _2 = const (); // scope 1 at $DIR/lower_intrinsics.rs:19:14: 19:41
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+ goto -> bb1; // scope 1 at $DIR/lower_intrinsics.rs:19:14: 19:41
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}
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bb1: {
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StorageDead(_3); // scope 1 at $DIR/lower_intrinsics.rs:19:40: 19:41
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StorageDead(_2); // scope 0 at $DIR/lower_intrinsics.rs:19:43: 19:44
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_0 = const (); // scope 0 at $DIR/lower_intrinsics.rs:18:24: 20:2
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return; // scope 0 at $DIR/lower_intrinsics.rs:20:2: 20:2
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}
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}
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‎src/test/mir-opt/lower_intrinsics.rs

+52
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// compile-flags: -Cpanic=abort
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#![feature(core_intrinsics)]
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#![crate_type = "lib"]
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// EMIT_MIR lower_intrinsics.wrapping.LowerIntrinsics.diff
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pub fn wrapping<T: Copy>(a: T, b: T) {
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let _x = core::intrinsics::wrapping_add(a, b);
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let _y = core::intrinsics::wrapping_sub(a, b);
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let _z = core::intrinsics::wrapping_mul(a, b);
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}
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// EMIT_MIR lower_intrinsics.size_of.LowerIntrinsics.diff
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pub fn size_of<T>() -> usize {
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core::intrinsics::size_of::<T>()
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}
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// EMIT_MIR lower_intrinsics.forget.LowerIntrinsics.diff
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pub fn forget<T>(t: T) {
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unsafe { core::intrinsics::forget(t) };
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}
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// EMIT_MIR lower_intrinsics.unreachable.LowerIntrinsics.diff
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pub fn unreachable() -> ! {
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unsafe { core::intrinsics::unreachable() };
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}
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// EMIT_MIR lower_intrinsics.f_unit.PreCodegen.before.mir
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pub fn f_unit() {
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f_dispatch(());
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}
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32+
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// EMIT_MIR lower_intrinsics.f_u64.PreCodegen.before.mir
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pub fn f_u64() {
35+
f_dispatch(0u64);
36+
}
37+
38+
#[inline(always)]
39+
pub fn f_dispatch<T>(t: T) {
40+
if std::mem::size_of::<T>() == 0 {
41+
f_zst(t);
42+
} else {
43+
f_non_zst(t);
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}
45+
}
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47+
#[inline(never)]
48+
pub fn f_zst<T>(t: T) {
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}
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#[inline(never)]
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pub fn f_non_zst<T>(t: T) {}

‎src/test/mir-opt/lower_intrinsics.size_of.LowerIntrinsics.diff

+20
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,20 @@
1+
- // MIR for `size_of` before LowerIntrinsics
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+ // MIR for `size_of` after LowerIntrinsics
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4+
fn size_of() -> usize {
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let mut _0: usize; // return place in scope 0 at $DIR/lower_intrinsics.rs:13:24: 13:29
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7+
bb0: {
8+
- _0 = std::intrinsics::size_of::<T>() -> bb1; // scope 0 at $DIR/lower_intrinsics.rs:14:5: 14:37
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- // mir::Constant
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- // + span: $DIR/lower_intrinsics.rs:14:5: 14:35
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- // + literal: Const { ty: extern "rust-intrinsic" fn() -> usize {std::intrinsics::size_of::<T>}, val: Value(Scalar(<ZST>)) }
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+ _0 = SizeOf(T); // scope 0 at $DIR/lower_intrinsics.rs:14:5: 14:37
13+
+ goto -> bb1; // scope 0 at $DIR/lower_intrinsics.rs:14:5: 14:37
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}
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bb1: {
17+
return; // scope 0 at $DIR/lower_intrinsics.rs:15:2: 15:2
18+
}
19+
}
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‎src/test/mir-opt/lower_intrinsics.unreachable.LowerIntrinsics.diff

+22
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,22 @@
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- // MIR for `unreachable` before LowerIntrinsics
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+ // MIR for `unreachable` after LowerIntrinsics
3+
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fn unreachable() -> ! {
5+
let mut _0: !; // return place in scope 0 at $DIR/lower_intrinsics.rs:23:25: 23:26
6+
let mut _1: !; // in scope 0 at $DIR/lower_intrinsics.rs:23:27: 25:2
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let _2: (); // in scope 0 at $DIR/lower_intrinsics.rs:24:14: 24:45
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let mut _3: !; // in scope 0 at $DIR/lower_intrinsics.rs:24:14: 24:45
9+
scope 1 {
10+
}
11+
12+
bb0: {
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StorageLive(_2); // scope 0 at $DIR/lower_intrinsics.rs:24:5: 24:47
14+
StorageLive(_3); // scope 1 at $DIR/lower_intrinsics.rs:24:14: 24:45
15+
- std::intrinsics::unreachable(); // scope 1 at $DIR/lower_intrinsics.rs:24:14: 24:45
16+
- // mir::Constant
17+
- // + span: $DIR/lower_intrinsics.rs:24:14: 24:43
18+
- // + literal: Const { ty: unsafe extern "rust-intrinsic" fn() -> ! {std::intrinsics::unreachable}, val: Value(Scalar(<ZST>)) }
19+
+ unreachable; // scope 1 at $DIR/lower_intrinsics.rs:24:14: 24:45
20+
}
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}
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