Add ability to unit-test dataflow results via `rustc_peek` intrinsic.

(The static semantics of `rustc_peek` is derived from attributes
attached to the function being compiled; in this case,
`rustc_peek(&expr)` observes the dataflow state for the l-value
`expr`.)

2 files changed, 208 insertions, 3 deletions

diff --git a/src/librustc_borrowck/borrowck/mir/dataflow/sanity_check.rs b/src/librustc_borrowck/borrowck/mir/dataflow/sanity_check.rs
new file mode 100644
index 00000000000..f74fb4ebadc
--- /dev/null
+++ b/src/librustc_borrowck/borrowck/mir/dataflow/sanity_check.rs
@@ -0,0 +1,193 @@
+// Copyright 2012-2016 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use syntax::abi::{Abi};
+use syntax::ast;
+
+use rustc::ty::{self, TyCtxt};
+use rustc::mir::repr::{self, Mir};
+
+use bitslice::BitSlice;
+
+use super::super::gather_moves::MovePath;
+use super::{bitwise, Union, Subtract};
+use super::BitDenotation;
+use super::DataflowResults;
+use super::HasMoveData;
+
+pub fn sanity_check_via_rustc_peek<'a, 'tcx, O>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
+                                                mir: &Mir<'tcx>,
+                                                id: ast::NodeId,
+                                                _attributes: &[ast::Attribute],
+                                                flow_ctxt: &O::Ctxt,
+                                                results: &DataflowResults<O>)
+    where O: BitDenotation<Bit=MovePath<'tcx>>, O::Ctxt: HasMoveData<'tcx>
+{
+    debug!("sanity_check_via_rustc_peek id: {:?}", id);
+    // FIXME: this is not DRY. Figure out way to abstract this and
+    // `dataflow::build_sets`. (But see note below about how the
+    // behavior of this traversal is a bit different than that
+    // performed by `build_sets`.)
+
+    let blocks = mir.all_basic_blocks();
+    'next_block: for bb in blocks {
+        let bb_data = mir.basic_block_data(bb);
+        let &repr::BasicBlockData { ref statements,
+                                    ref terminator,
+                                    is_cleanup: _ } = bb_data;
+
+        let (args, span) = if let Some(repr::Terminator { ref kind, span, .. }) = *terminator {
+            if let repr::TerminatorKind::Call { func: ref oper, ref args, .. } = *kind
+            {
+                if let repr::Operand::Constant(ref func) = *oper
+                {
+                    if let ty::TyFnDef(def_id, _, &ty::BareFnTy { abi, .. }) = func.ty.sty
+                    {
+                        let name = tcx.item_name(def_id);
+                        if abi == Abi::RustIntrinsic || abi == Abi::PlatformIntrinsic {
+                            if name.as_str() == "rustc_peek" {
+                                (args, span)
+                            } else {
+                                continue;
+                            }
+                        } else {
+                            continue;
+                        }
+                    } else {
+                        continue;
+                    }
+                } else {
+                    continue;
+                }
+            } else {
+                continue;
+            }
+        } else {
+            continue;
+        };
+        assert!(args.len() == 1);
+        let peek_arg_lval = match args[0] {
+            repr::Operand::Consume(ref lval @ repr::Lvalue::Temp(_)) => {
+                lval
+            }
+            repr::Operand::Consume(_) => {
+                bug!("dataflow::sanity_check cannot feed a non-temp to rustc_peek.");
+            }
+            repr::Operand::Constant(_) => {
+                bug!("dataflow::sanity_check cannot feed a constant to rustc_peek.");
+            }
+        };
+
+        let mut entry = results.0.sets.on_entry_set_for(bb.index()).to_owned();
+        let mut gen = results.0.sets.gen_set_for(bb.index()).to_owned();
+        let mut kill = results.0.sets.kill_set_for(bb.index()).to_owned();
+
+        let move_data = flow_ctxt.move_data();
+
+        // Emulate effect of all statements in the block up to (but
+        // not including) the assignment to `peek_arg_lval`. Do *not*
+        // include terminator (since we are peeking the state of the
+        // argument at time immediate preceding Call to `rustc_peek`).
+
+        let mut sets = super::BlockSets { on_entry: &mut entry[..],
+                                          gen_set: &mut gen[..],
+                                          kill_set: &mut kill[..] };
+        // Unfortunately if we just re-do the same thing that dataflow does, then
+        // it will always appear like Lvalues are initialized; e.g. in
+        // a case like:
+        //
+        // <bitset maps var1 to 0>
+        // tmp13 = var1;
+        // tmp14 = &tmp13;
+        // rustc_peek(tmp14)
+        //
+        // The gen_set for normal dataflow would treat tmp13 as
+        // initialized, even though it's source expression is
+        // uninitialized.
+        //
+        // Work around this for rustc_peek by explicitly propagating
+        // the relevant bitvector state when computing the effect of a
+        // statement.
+
+        for (j, stmt) in statements.iter().enumerate() {
+            debug!("rustc_peek: ({:?},{}) {:?}", bb, j, stmt);
+            let (lvalue, rvalue) = match stmt.kind {
+                repr::StatementKind::Assign(ref lvalue, ref rvalue) => {
+                    (lvalue, rvalue)
+                }
+            };
+
+            if lvalue == peek_arg_lval {
+                if let repr::Rvalue::Ref(_,
+                                         repr::BorrowKind::Shared,
+                                         ref peeking_at_lval) = *rvalue {
+                    // Okay, our search is over.
+                    let peek_mpi = move_data.rev_lookup.find(peeking_at_lval);
+                    let bit_state = sets.on_entry.get_bit(peek_mpi.idx());
+                    debug!("rustc_peek({:?} = &{:?}) bit_state: {}",
+                           lvalue, peeking_at_lval, bit_state);
+                    if !bit_state {
+                        tcx.sess.span_err(span, &format!("rustc_peek: bit not set"));
+                    }
+                    continue 'next_block;
+                } else {
+                    // Our search should have been over, but the input
+                    // does not match expectations of `rustc_peek` for
+                    // this sanity_check.
+                    tcx.sess.span_err(span, &format!("rustc_peek: argument expression \
+                                                      must be immediate borrow of form `&expr`"));
+                }
+            }
+
+            enum Effect<'a, 'tcx:'a> { Propagate(&'a repr::Lvalue<'tcx>), Compute }
+            let lvalue_effect: Effect = match *rvalue {
+                // tmp = rhs
+                repr::Rvalue::Use(repr::Operand::Consume(ref rhs_lval)) =>
+                    Effect::Propagate(rhs_lval),
+
+                repr::Rvalue::Use(repr::Operand::Constant(_)) =>
+                    Effect::Compute,
+
+                _ => {
+                    // (fall back to BitDenotation for all other kinds of Rvalues
+                    Effect::Compute
+                }
+            };
+
+            let lhs_mpi = move_data.rev_lookup.find(lvalue);
+
+            if let Effect::Propagate(rhs_lval) = lvalue_effect {
+                let rhs_mpi = move_data.rev_lookup.find(rhs_lval);
+                let state = sets.on_entry.get_bit(rhs_mpi.idx());
+                debug!("rustc_peek: propagate into lvalue {:?} ({:?}) from rhs: {:?} state: {}",
+                       lvalue, lhs_mpi, rhs_lval, state);
+                if state {
+                    sets.on_entry.set_bit(lhs_mpi.idx());
+                } else {
+                    sets.on_entry.clear_bit(lhs_mpi.idx());
+                }
+            } else {
+                debug!("rustc_peek: computing effect on lvalue: {:?} ({:?}) in stmt: {:?}",
+                       lvalue, lhs_mpi, stmt);
+                // reset GEN and KILL sets before emulating their effect.
+                for e in &mut sets.gen_set[..] { *e = 0; }
+                for e in &mut sets.kill_set[..] { *e = 0; }
+                results.0.operator.statement_effect(flow_ctxt, &mut sets, bb, j);
+                bitwise(sets.on_entry, sets.gen_set, &Union);
+                bitwise(sets.on_entry, sets.kill_set, &Subtract);
+            }
+        }
+
+        tcx.sess.span_err(span, &format!("rustc_peek: MIR did not match \
+                                          anticipated pattern; note that \
+                                          rustc_peek expects input of \
+                                          form `&expr`"));
+    }
+}
diff --git a/src/librustc_borrowck/borrowck/mir/mod.rs b/src/librustc_borrowck/borrowck/mir/mod.rs
index 44a53a23528..ce49e9fc93d 100644
--- a/src/librustc_borrowck/borrowck/mir/mod.rs
+++ b/src/librustc_borrowck/borrowck/mir/mod.rs
@@ -75,9 +75,21 @@ pub fn borrowck_mir<'a, 'tcx: 'a>(
     let move_data = MoveData::gather_moves(mir, tcx);
     let ctxt = (tcx, mir, move_data);
     let (ctxt, flow_inits) =
-        do_dataflow(bcx, mir, id, attributes, ctxt, MaybeInitializedLvals::default());
-    let ((_, _, move_data), flow_uninits) =
-        do_dataflow(bcx, mir, id, attributes, ctxt, MaybeUninitializedLvals::default());
+        do_dataflow(tcx, mir, id, attributes, ctxt, MaybeInitializedLvals::default());
+    let (ctxt, flow_uninits) =
+        do_dataflow(tcx, mir, id, attributes, ctxt, MaybeUninitializedLvals::default());
+
+    if has_rustc_mir_with(attributes, "rustc_peek_maybe_init").is_some() {
+        dataflow::sanity_check_via_rustc_peek(bcx.tcx, mir, id, attributes, &ctxt, &flow_inits);
+    }
+    if has_rustc_mir_with(attributes, "rustc_peek_maybe_uninit").is_some() {
+        dataflow::sanity_check_via_rustc_peek(bcx.tcx, mir, id, attributes, &ctxt, &flow_uninits);
+    }
+    let move_data = ctxt.2;
+
+    if has_rustc_mir_with(attributes, "stop_after_dataflow").is_some() {
+        bcx.tcx.sess.fatal("stop_after_dataflow ended compilation");
+    }
 
     let mut mbcx = MirBorrowckCtxt {
         bcx: bcx,