scaffolding for borrowck on MIR.

emit (via debug!) scary message from `fn borrowck_mir` until basic
prototype is in place.

Gather children of move paths and set their kill bits in
dataflow. (Each node has a link to the child that is first among its
siblings.)

Hooked in libgraphviz based rendering, including of borrowck dataflow
state.

doing this well required some refactoring of the code, so I cleaned it
up more generally (adding comments to explain what its trying to do
and how it is doing it).

Update: this newer version addresses most review comments (at least
the ones that were largely mechanical changes), but I left the more
interesting revisions to separate followup commits (in this same PR).

mk/crates.mk

@@ -97,7 +97,7 @@ DEPS_rustc := syntax fmt_macros flate arena serialize getopts rbml rustc_front\
               log graphviz rustc_llvm rustc_back rustc_data_structures\
 		  	  rustc_const_eval
 DEPS_rustc_back := std syntax rustc_llvm rustc_front flate log libc
-DEPS_rustc_borrowck := rustc rustc_front log graphviz syntax
+DEPS_rustc_borrowck := rustc rustc_front rustc_mir log graphviz syntax
 DEPS_rustc_data_structures := std log serialize
 DEPS_rustc_driver := arena flate getopts graphviz libc rustc rustc_back rustc_borrowck \
                      rustc_typeck rustc_mir rustc_resolve log syntax serialize rustc_llvm \

src/librustc/middle/dataflow.rs

@@ -653,7 +653,7 @@ fn set_bit(words: &mut [usize], bit: usize) -> bool {
     let word = bit / usize_bits;
     let bit_in_word = bit % usize_bits;
     let bit_mask = 1 << bit_in_word;
-    debug!("word={} bit_in_word={} bit_mask={}", word, bit_in_word, word);
+    debug!("word={} bit_in_word={} bit_mask={}", word, bit_in_word, bit_mask);
     let oldv = words[word];
     let newv = oldv | bit_mask;
     words[word] = newv;

src/librustc/mir/repr.rs

@@ -499,13 +499,13 @@ pub enum Lvalue<'tcx> {
 /// or `*B` or `B[index]`. Note that it is parameterized because it is
 /// shared between `Constant` and `Lvalue`. See the aliases
 /// `LvalueProjection` etc below.
-#[derive(Clone, Debug, PartialEq, RustcEncodable, RustcDecodable)]
+#[derive(Clone, Debug, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable)]
 pub struct Projection<'tcx, B, V> {
     pub base: B,
     pub elem: ProjectionElem<'tcx, V>,
 }
 
-#[derive(Clone, Debug, PartialEq, RustcEncodable, RustcDecodable)]
+#[derive(Clone, Debug, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable)]
 pub enum ProjectionElem<'tcx, V> {
     Deref,
     Field(Field, Ty<'tcx>),
@@ -857,7 +857,7 @@ impl<'tcx> Debug for Rvalue<'tcx> {
 /// this does not necessarily mean that they are "==" in Rust -- in
 /// particular one must be wary of `NaN`!
 
-#[derive(Clone, PartialEq, RustcEncodable, RustcDecodable)]
+#[derive(Clone, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable)]
 pub struct Constant<'tcx> {
     pub span: Span,
     pub ty: Ty<'tcx>,
@@ -877,7 +877,7 @@ impl<'tcx> Debug for TypedConstVal<'tcx> {
     }
 }
 
-#[derive(Clone, PartialEq, RustcEncodable, RustcDecodable)]
+#[derive(Clone, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable)]
 pub enum Literal<'tcx> {
     Item {
         def_id: DefId,

src/librustc_borrowck/bitslice.rs

@@ -0,0 +1,82 @@
+// 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 std::mem;
+
+/// `BitSlice` provides helper methods for treating a `[usize]`
+/// as a bitvector.
+pub trait BitSlice {
+    fn set_bit(&mut self, idx: usize) -> bool;
+    fn get_bit(&self, idx: usize) -> bool;
+}
+
+impl BitSlice for [usize] {
+    fn set_bit(&mut self, idx: usize) -> bool {
+        let words = self;
+        debug!("set_bit: words={} idx={}",
+               bits_to_string(words, words.len() * mem::size_of::<usize>()), bit_str(idx));
+        let BitLookup { word, bit_in_word, bit_mask } = bit_lookup(idx);
+        debug!("word={} bit_in_word={} bit_mask={}", word, bit_in_word, bit_mask);
+        let oldv = words[word];
+        let newv = oldv | bit_mask;
+        words[word] = newv;
+        oldv != newv
+    }
+
+    fn get_bit(&self, idx: usize) -> bool {
+        let words = self;
+        let BitLookup { word, bit_mask, .. } = bit_lookup(idx);
+        (words[word] & bit_mask) != 0
+    }
+}
+
+struct BitLookup { word: usize, bit_in_word: usize, bit_mask: usize }
+
+#[inline]
+fn bit_lookup(bit: usize) -> BitLookup {
+    let usize_bits = mem::size_of::<usize>() * 8;
+    let word = bit / usize_bits;
+    let bit_in_word = bit % usize_bits;
+    let bit_mask = 1 << bit_in_word;
+    BitLookup { word: word, bit_in_word: bit_in_word, bit_mask: bit_mask }
+}
+
+
+fn bit_str(bit: usize) -> String {
+    let byte = bit >> 8;
+    let lobits = 1 << (bit & 0xFF);
+    format!("[{}:{}-{:02x}]", bit, byte, lobits)
+}
+
+pub fn bits_to_string(words: &[usize], bytes: usize) -> String {
+    let mut result = String::new();
+    let mut sep = '[';
+
+    // Note: this is a little endian printout of bytes.
+
+    let mut i = 0;
+    for &word in words.iter() {
+        let mut v = word;
+        for _ in 0..mem::size_of::<usize>() {
+            let byte = v & 0xFF;
+            if i >= bytes {
+                assert!(byte == 0);
+            } else {
+                result.push(sep);
+                result.push_str(&format!("{:02x}", byte));
+            }
+            v >>= 8;
+            i += 1;
+            sep = '-';
+        }
+    }
+    result.push(']');
+    return result
+}

src/librustc_borrowck/borrowck/mir/abs_domain.rs

@@ -0,0 +1,62 @@
+// 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.
+
+//! The move-analysis portion of borrowck needs to work in an abstract
+//! domain of lifted Lvalues.  Most of the Lvalue variants fall into a
+//! one-to-one mapping between the concrete and abstract (e.g. a
+//! field-deref on a local-variable, `x.field`, has the same meaning
+//! in both domains). Indexed-Projections are the exception: `a[x]`
+//! needs to be treated as mapping to the same move path as `a[y]` as
+//! well as `a[13]`, et cetera.
+//!
+//! (In theory the analysis could be extended to work with sets of
+//! paths, so that `a[0]` and `a[13]` could be kept distinct, while
+//! `a[x]` would still overlap them both. But that is not this
+//! representation does today.)
+
+use rustc::mir::repr::{Lvalue, LvalueElem};
+use rustc::mir::repr::{Operand, Projection, ProjectionElem};
+
+#[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
+pub struct AbstractOperand;
+pub type AbstractProjection<'tcx> =
+    Projection<'tcx, Lvalue<'tcx>, AbstractOperand>;
+pub type AbstractElem<'tcx> =
+    ProjectionElem<'tcx, AbstractOperand>;
+
+pub trait Lift {
+    type Abstract;
+    fn lift(&self) -> Self::Abstract;
+}
+impl<'tcx> Lift for Operand<'tcx> {
+    type Abstract = AbstractOperand;
+    fn lift(&self) -> Self::Abstract { AbstractOperand }
+}
+impl<'tcx> Lift for LvalueElem<'tcx> {
+    type Abstract = AbstractElem<'tcx>;
+    fn lift(&self) -> Self::Abstract {
+        match *self {
+            ProjectionElem::Deref =>
+                ProjectionElem::Deref,
+            ProjectionElem::Field(ref f, ty) =>
+                ProjectionElem::Field(f.clone(), ty.clone()),
+            ProjectionElem::Index(ref i) =>
+                ProjectionElem::Index(i.lift()),
+            ProjectionElem::ConstantIndex {offset,min_length,from_end} =>
+                ProjectionElem::ConstantIndex {
+                    offset: offset,
+                    min_length: min_length,
+                    from_end: from_end
+                },
+            ProjectionElem::Downcast(a, u) =>
+                ProjectionElem::Downcast(a.clone(), u.clone()),
+        }
+    }
+}