b611b6bbb8
GVN is actually on in release, and covers all the same things (or more), with `LowerSliceLen` changed to produce `PtrMetadata`.
68 lines
2.3 KiB
Rust
68 lines
2.3 KiB
Rust
//! This pass lowers calls to core::slice::len to just PtrMetadata op.
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//! It should run before inlining!
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use rustc_hir::def_id::DefId;
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use rustc_middle::mir::*;
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use rustc_middle::ty::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.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 lang 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 = body.basic_blocks.as_mut_preserves_cfg();
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for block in basic_blocks {
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// lower `<[_]>::len` calls
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lower_slice_len_call(block, slice_len_fn_item_def_id);
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}
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}
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fn lower_slice_len_call<'tcx>(block: &mut BasicBlockData<'tcx>, slice_len_fn_item_def_id: DefId) {
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let terminator = block.terminator();
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if let 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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call_source: CallSource::Normal,
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..
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} = &terminator.kind
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// some heuristics for fast rejection
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&& let [arg] = &args[..]
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&& let Some((fn_def_id, _)) = func.const_fn_def()
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&& fn_def_id == slice_len_fn_item_def_id
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{
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// perform modifications from something like:
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// _5 = core::slice::<impl [u8]>::len(move _6) -> bb1
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// into:
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// _5 = PtrMetadata(move _6)
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// goto bb1
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// make new RValue for Len
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let r_value = Rvalue::UnaryOp(UnOp::PtrMetadata, arg.node.clone());
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let len_statement_kind = 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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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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