102 lines
3.4 KiB
Rust
102 lines
3.4 KiB
Rust
//! This pass lowers calls to core::slice::len to just Len op.
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//! It should run before inlining!
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use crate::MirPass;
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use rustc_hir::def_id::DefId;
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use rustc_index::vec::IndexVec;
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use rustc_middle::mir::*;
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use rustc_middle::ty::{self, TyCtxt};
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pub struct LowerSliceLenCalls;
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impl<'tcx> MirPass<'tcx> for LowerSliceLenCalls {
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fn is_enabled(&self, sess: &rustc_session::Session) -> bool {
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sess.opts.mir_opt_level() > 0
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}
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fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
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lower_slice_len_calls(tcx, body)
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}
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}
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pub fn lower_slice_len_calls<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
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let language_items = tcx.lang_items();
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let Some(slice_len_fn_item_def_id) = language_items.slice_len_fn() else {
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// there is no language item to compare to :)
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return;
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};
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// The one successor remains unchanged, so no need to invalidate
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let (basic_blocks, local_decls, _) =
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body.basic_blocks_local_decls_mut_and_var_debug_info_no_invalidate();
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for block in basic_blocks {
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// lower `<[_]>::len` calls
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lower_slice_len_call(tcx, block, &*local_decls, slice_len_fn_item_def_id);
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}
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}
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struct SliceLenPatchInformation<'tcx> {
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add_statement: Statement<'tcx>,
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new_terminator_kind: TerminatorKind<'tcx>,
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}
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fn lower_slice_len_call<'tcx>(
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tcx: TyCtxt<'tcx>,
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block: &mut BasicBlockData<'tcx>,
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local_decls: &IndexVec<Local, LocalDecl<'tcx>>,
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slice_len_fn_item_def_id: DefId,
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) {
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let mut patch_found: Option<SliceLenPatchInformation<'_>> = None;
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let terminator = block.terminator();
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match &terminator.kind {
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TerminatorKind::Call {
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func,
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args,
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destination,
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target: Some(bb),
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cleanup: None,
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from_hir_call: true,
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..
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} => {
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// some heuristics for fast rejection
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if args.len() != 1 {
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return;
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}
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let Some(arg) = args[0].place() else { return };
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let func_ty = func.ty(local_decls, tcx);
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match func_ty.kind() {
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ty::FnDef(fn_def_id, _) if fn_def_id == &slice_len_fn_item_def_id => {
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// perform modifications
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// from something like `_5 = core::slice::<impl [u8]>::len(move _6) -> bb1`
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// into `_5 = Len(*_6)
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// goto bb1
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// make new RValue for Len
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let deref_arg = tcx.mk_place_deref(arg);
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let r_value = Rvalue::Len(deref_arg);
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let len_statement_kind =
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StatementKind::Assign(Box::new((*destination, r_value)));
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let add_statement =
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Statement { kind: len_statement_kind, source_info: terminator.source_info };
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// modify terminator into simple Goto
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let new_terminator_kind = TerminatorKind::Goto { target: *bb };
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let patch = SliceLenPatchInformation { add_statement, new_terminator_kind };
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patch_found = Some(patch);
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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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if let Some(SliceLenPatchInformation { add_statement, new_terminator_kind }) = patch_found {
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block.statements.push(add_statement);
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block.terminator_mut().kind = new_terminator_kind;
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}
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}
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