Auto merge of #35854 - nikomatsakis:incr-comp-cache-hash-35549, r=mw

compute and cache HIR hashes at beginning

This avoids the compile-time overhead of computing them twice.  It also fixes
an issue where the hash computed after typeck is differen than the hash before,
because typeck mutates the def-map in place.

Fixes #35549.
Fixes #35593.

Some performance measurements suggest this `HashesMap` is very small in memory (unobservable via `-Z time-passes`) and very cheap to construct. I do see some (very minor) performance wins in the incremental case after the first run -- the first run costs more because loading the dep-graph didn't have any hashing to do in that case. Example timings from two runs  of `libsyntex-syntax` -- the (1) indicates first run, (2) indicates second run, and (*) indicates both together:

| Phase | Master | Branch |
| ---- | ---- | ---- |
| compute_hashes_map (1) | N/A | 0.343 |
| load_dep_graph (1) | 0 | 0 |
| serialize dep graph (1) | 4.190 | 3.920 |
| total (1) | 4.190 | 4.260 |
| compute_hashes_map (2) | N/A | 0.344 |
| load_dep_graph (2) | 0.592 | 0.252 |
| serialize dep graph (2) | 4.119 | 3.779 |
| total (2) | 4.71 | 4.375 |
| total (*) | 8.9 | 8.635 |

r? @michaelwoerister

19 files changed, 350 insertions, 176 deletions

diff --git a/src/librustc/dep_graph/dep_node.rs b/src/librustc/dep_graph/dep_node.rs
index 40fd3dede3d..e95fbcc8917 100644
--- a/src/librustc/dep_graph/dep_node.rs
+++ b/src/librustc/dep_graph/dep_node.rs
@@ -147,6 +147,11 @@ impl<D: Clone + Debug> DepNode<D> {
             }
         }
 
+        if label == "Krate" {
+            // special case
+            return Ok(DepNode::Krate);
+        }
+
         check! {
             CollectItem,
             BorrowCheck,
diff --git a/src/librustc/hir/mod.rs b/src/librustc/hir/mod.rs
index d41cdfabdf4..99fb2d6a449 100644
--- a/src/librustc/hir/mod.rs
+++ b/src/librustc/hir/mod.rs
@@ -1621,7 +1621,7 @@ pub type FreevarMap = NodeMap<Vec<Freevar>>;
 
 pub type CaptureModeMap = NodeMap<CaptureClause>;
 
-#[derive(Clone)]
+#[derive(Clone, Debug)]
 pub struct TraitCandidate {
     pub def_id: DefId,
     pub import_id: Option<NodeId>,
diff --git a/src/librustc_driver/driver.rs b/src/librustc_driver/driver.rs
index c6100004786..3f2f6c84da1 100644
--- a/src/librustc_driver/driver.rs
+++ b/src/librustc_driver/driver.rs
@@ -26,7 +26,7 @@ use rustc::util::common::time;
 use rustc::util::nodemap::NodeSet;
 use rustc_back::sha2::{Sha256, Digest};
 use rustc_borrowck as borrowck;
-use rustc_incremental;
+use rustc_incremental::{self, IncrementalHashesMap};
 use rustc_resolve::{MakeGlobMap, Resolver};
 use rustc_metadata::macro_import;
 use rustc_metadata::creader::read_local_crates;
@@ -172,7 +172,7 @@ pub fn compile_input(sess: &Session,
                                     resolutions,
                                     &arenas,
                                     &crate_name,
-                                    |tcx, mir_map, analysis, result| {
+                                    |tcx, mir_map, analysis, incremental_hashes_map, result| {
             {
                 // Eventually, we will want to track plugins.
                 let _ignore = tcx.dep_graph.in_ignore();
@@ -202,7 +202,8 @@ pub fn compile_input(sess: &Session,
             }
             let trans = phase_4_translate_to_llvm(tcx,
                                                   mir_map.unwrap(),
-                                                  analysis);
+                                                  analysis,
+                                                  &incremental_hashes_map);
 
             if log_enabled!(::log::INFO) {
                 println!("Post-trans");
@@ -797,14 +798,15 @@ pub fn phase_3_run_analysis_passes<'tcx, F, R>(sess: &'tcx Session,
     where F: for<'a> FnOnce(TyCtxt<'a, 'tcx, 'tcx>,
                             Option<MirMap<'tcx>>,
                             ty::CrateAnalysis,
+                            IncrementalHashesMap,
                             CompileResult) -> R
 {
     macro_rules! try_with_f {
-        ($e: expr, ($t: expr, $m: expr, $a: expr)) => {
+        ($e: expr, ($t: expr, $m: expr, $a: expr, $h: expr)) => {
             match $e {
                 Ok(x) => x,
                 Err(x) => {
-                    f($t, $m, $a, Err(x));
+                    f($t, $m, $a, $h, Err(x));
                     return Err(x);
                 }
             }
@@ -860,12 +862,16 @@ pub fn phase_3_run_analysis_passes<'tcx, F, R>(sess: &'tcx Session,
                              index,
                              name,
                              |tcx| {
+        let incremental_hashes_map =
+            time(time_passes,
+                 "compute_incremental_hashes_map",
+                 || rustc_incremental::compute_incremental_hashes_map(tcx));
         time(time_passes,
              "load_dep_graph",
-             || rustc_incremental::load_dep_graph(tcx));
+             || rustc_incremental::load_dep_graph(tcx, &incremental_hashes_map));
 
         // passes are timed inside typeck
-        try_with_f!(typeck::check_crate(tcx), (tcx, None, analysis));
+        try_with_f!(typeck::check_crate(tcx), (tcx, None, analysis, incremental_hashes_map));
 
         time(time_passes,
              "const checking",
@@ -935,7 +941,11 @@ pub fn phase_3_run_analysis_passes<'tcx, F, R>(sess: &'tcx Session,
         // lint warnings and so on -- kindck used to do this abort, but
         // kindck is gone now). -nmatsakis
         if sess.err_count() > 0 {
-            return Ok(f(tcx, Some(mir_map), analysis, Err(sess.err_count())));
+            return Ok(f(tcx,
+                        Some(mir_map),
+                        analysis,
+                        incremental_hashes_map,
+                        Err(sess.err_count())));
         }
 
         analysis.reachable =
@@ -963,17 +973,22 @@ pub fn phase_3_run_analysis_passes<'tcx, F, R>(sess: &'tcx Session,
 
         // The above three passes generate errors w/o aborting
         if sess.err_count() > 0 {
-            return Ok(f(tcx, Some(mir_map), analysis, Err(sess.err_count())));
+            return Ok(f(tcx,
+                        Some(mir_map),
+                        analysis,
+                        incremental_hashes_map,
+                        Err(sess.err_count())));
         }
 
-        Ok(f(tcx, Some(mir_map), analysis, Ok(())))
+        Ok(f(tcx, Some(mir_map), analysis, incremental_hashes_map, Ok(())))
     })
 }
 
 /// Run the translation phase to LLVM, after which the AST and analysis can
 pub fn phase_4_translate_to_llvm<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                                            mut mir_map: MirMap<'tcx>,
-                                           analysis: ty::CrateAnalysis)
+                                           analysis: ty::CrateAnalysis,
+                                           incremental_hashes_map: &IncrementalHashesMap)
                                            -> trans::CrateTranslation {
     let time_passes = tcx.sess.time_passes();
 
@@ -1007,7 +1022,7 @@ pub fn phase_4_translate_to_llvm<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
     let translation =
         time(time_passes,
              "translation",
-             move || trans::trans_crate(tcx, &mir_map, analysis));
+             move || trans::trans_crate(tcx, &mir_map, analysis, &incremental_hashes_map));
 
     time(time_passes,
          "assert dep graph",
@@ -1015,7 +1030,7 @@ pub fn phase_4_translate_to_llvm<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 
     time(time_passes,
          "serialize dep graph",
-         move || rustc_incremental::save_dep_graph(tcx));
+         move || rustc_incremental::save_dep_graph(tcx, &incremental_hashes_map));
 
     translation
 }
diff --git a/src/librustc_driver/pretty.rs b/src/librustc_driver/pretty.rs
index e3e06963ad4..1ffeaf322bf 100644
--- a/src/librustc_driver/pretty.rs
+++ b/src/librustc_driver/pretty.rs
@@ -234,7 +234,7 @@ impl PpSourceMode {
                                                                  resolutions.clone(),
                                                                  arenas,
                                                                  id,
-                                                                 |tcx, _, _, _| {
+                                                                 |tcx, _, _, _, _| {
                     let annotation = TypedAnnotation {
                         tcx: tcx,
                     };
@@ -951,7 +951,7 @@ fn print_with_analysis<'tcx, 'a: 'tcx>(sess: &'a Session,
                                                      resolutions.clone(),
                                                      arenas,
                                                      crate_name,
-                                                     |tcx, mir_map, _, _| {
+                                                     |tcx, mir_map, _, _, _| {
         match ppm {
             PpmMir | PpmMirCFG => {
                 if let Some(mir_map) = mir_map {
diff --git a/src/librustc_incremental/calculate_svh/def_path_hash.rs b/src/librustc_incremental/calculate_svh/def_path_hash.rs
new file mode 100644
index 00000000000..8aa134ba3bf
--- /dev/null
+++ b/src/librustc_incremental/calculate_svh/def_path_hash.rs
@@ -0,0 +1,36 @@
+// Copyright 2012-2014 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 rustc::hir::def_id::DefId;
+use rustc::ty::TyCtxt;
+use rustc::util::nodemap::DefIdMap;
+
+pub struct DefPathHashes<'a, 'tcx: 'a> {
+    tcx: TyCtxt<'a, 'tcx, 'tcx>,
+    data: DefIdMap<u64>,
+}
+
+impl<'a, 'tcx> DefPathHashes<'a, 'tcx> {
+    pub fn new(tcx: TyCtxt<'a, 'tcx, 'tcx>) -> Self {
+        DefPathHashes {
+            tcx: tcx,
+            data: DefIdMap()
+        }
+    }
+
+    pub fn hash(&mut self, def_id: DefId) -> u64 {
+        let tcx = self.tcx;
+        *self.data.entry(def_id)
+                  .or_insert_with(|| {
+                      let def_path = tcx.def_path(def_id);
+                      def_path.deterministic_hash(tcx)
+                  })
+    }
+}
diff --git a/src/librustc_incremental/calculate_svh/mod.rs b/src/librustc_incremental/calculate_svh/mod.rs
index d7caf8c882f..42bb1a52467 100644
--- a/src/librustc_incremental/calculate_svh/mod.rs
+++ b/src/librustc_incremental/calculate_svh/mod.rs
@@ -8,106 +8,137 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-//! Calculation of a Strict Version Hash for crates.  For a length
-//! comment explaining the general idea, see `librustc/middle/svh.rs`.
-
+//! Calculation of the (misnamed) "strict version hash" for crates and
+//! items. This hash is used to tell when the HIR changed in such a
+//! way that results from previous compilations may no longer be
+//! applicable and hence must be recomputed. It should probably be
+//! renamed to the ICH (incremental compilation hash).
+//!
+//! The hashes for all items are computed once at the beginning of
+//! compilation and stored into a map. In addition, a hash is computed
+//! of the **entire crate**.
+//!
+//! Storing the hashes in a map avoids the need to compute them twice
+//! (once when loading prior incremental results and once when
+//! saving), but it is also important for correctness: at least as of
+//! the time of this writing, the typeck passes rewrites entries in
+//! the dep-map in-place to accommodate UFCS resolutions. Since name
+//! resolution is part of the hash, the result is that hashes computed
+//! at the end of compilation would be different from those computed
+//! at the beginning.
+
+use syntax::ast;
 use syntax::attr::AttributeMethods;
 use std::hash::{Hash, SipHasher, Hasher};
+use rustc::dep_graph::DepNode;
+use rustc::hir;
 use rustc::hir::def_id::{CRATE_DEF_INDEX, DefId};
-use rustc::hir::map::{NodeItem, NodeForeignItem};
-use rustc::hir::svh::Svh;
+use rustc::hir::intravisit as visit;
 use rustc::ty::TyCtxt;
-use rustc::hir::intravisit::{self, Visitor};
+use rustc_data_structures::fnv::FnvHashMap;
 
+use self::def_path_hash::DefPathHashes;
 use self::svh_visitor::StrictVersionHashVisitor;
 
+mod def_path_hash;
 mod svh_visitor;
 
-pub trait SvhCalculate {
-    /// Calculate the SVH for an entire krate.
-    fn calculate_krate_hash(self) -> Svh;
-
-    /// Calculate the SVH for a particular item.
-    fn calculate_item_hash(self, def_id: DefId) -> u64;
+pub type IncrementalHashesMap = FnvHashMap<DepNode<DefId>, u64>;
+
+pub fn compute_incremental_hashes_map<'a, 'tcx: 'a>(tcx: TyCtxt<'a, 'tcx, 'tcx>)
+                                                    -> IncrementalHashesMap {
+    let _ignore = tcx.dep_graph.in_ignore();
+    let krate = tcx.map.krate();
+    let mut visitor = HashItemsVisitor { tcx: tcx,
+                                         hashes: FnvHashMap(),
+                                         def_path_hashes: DefPathHashes::new(tcx) };
+    visitor.calculate_def_id(DefId::local(CRATE_DEF_INDEX), |v| visit::walk_crate(v, krate));
+    krate.visit_all_items(&mut visitor);
+    visitor.compute_crate_hash();
+    visitor.hashes
 }
 
-impl<'a, 'tcx> SvhCalculate for TyCtxt<'a, 'tcx, 'tcx> {
-    fn calculate_krate_hash(self) -> Svh {
-        // FIXME (#14132): This is better than it used to be, but it still not
-        // ideal. We now attempt to hash only the relevant portions of the
-        // Crate AST as well as the top-level crate attributes. (However,
-        // the hashing of the crate attributes should be double-checked
-        // to ensure it is not incorporating implementation artifacts into
-        // the hash that are not otherwise visible.)
+struct HashItemsVisitor<'a, 'tcx: 'a> {
+    tcx: TyCtxt<'a, 'tcx, 'tcx>,
+    def_path_hashes: DefPathHashes<'a, 'tcx>,
+    hashes: IncrementalHashesMap,
+}
 
-        let crate_disambiguator = self.sess.local_crate_disambiguator();
-        let krate = self.map.krate();
+impl<'a, 'tcx> HashItemsVisitor<'a, 'tcx> {
+    fn calculate_node_id<W>(&mut self, id: ast::NodeId, walk_op: W)
+        where W: for<'v> FnMut(&mut StrictVersionHashVisitor<'v, 'a, 'tcx>)
+    {
+        let def_id = self.tcx.map.local_def_id(id);
+        self.calculate_def_id(def_id, walk_op)
+    }
 
-        // FIXME: this should use SHA1, not SipHash. SipHash is not built to
-        //        avoid collisions.
+    fn calculate_def_id<W>(&mut self, def_id: DefId, mut walk_op: W)
+        where W: for<'v> FnMut(&mut StrictVersionHashVisitor<'v, 'a, 'tcx>)
+    {
+        assert!(def_id.is_local());
+        debug!("HashItemsVisitor::calculate(def_id={:?})", def_id);
+        // FIXME: this should use SHA1, not SipHash. SipHash is not
+        // built to avoid collisions.
         let mut state = SipHasher::new();
-        debug!("state: {:?}", state);
+        walk_op(&mut StrictVersionHashVisitor::new(&mut state,
+                                                   self.tcx,
+                                                   &mut self.def_path_hashes));
+        let item_hash = state.finish();
+        self.hashes.insert(DepNode::Hir(def_id), item_hash);
+        debug!("calculate_item_hash: def_id={:?} hash={:?}", def_id, item_hash);
+    }
+
+    fn compute_crate_hash(&mut self) {
+        let krate = self.tcx.map.krate();
 
-        // FIXME(#32753) -- at (*) we `to_le` for endianness, but is
-        // this enough, and does it matter anyway?
-        "crate_disambiguator".hash(&mut state);
-        crate_disambiguator.len().to_le().hash(&mut state); // (*)
-        crate_disambiguator.hash(&mut state);
+        let mut crate_state = SipHasher::new();
 
-        debug!("crate_disambiguator: {:?}", crate_disambiguator);
-        debug!("state: {:?}", state);
+        let crate_disambiguator = self.tcx.sess.local_crate_disambiguator();
+        "crate_disambiguator".hash(&mut crate_state);
+        crate_disambiguator.len().hash(&mut crate_state);
+        crate_disambiguator.hash(&mut crate_state);
 
+        // add each item (in some deterministic order) to the overall
+        // crate hash.
         {
-            let mut visit = StrictVersionHashVisitor::new(&mut state, self);
-            krate.visit_all_items(&mut visit);
+            let def_path_hashes = &mut self.def_path_hashes;
+            let mut item_hashes: Vec<_> =
+                self.hashes.iter()
+                           .map(|(item_dep_node, &item_hash)| {
+                               // convert from a DepNode<DefId> tp a
+                               // DepNode<u64> where the u64 is the
+                               // hash of the def-id's def-path:
+                               let item_dep_node =
+                                   item_dep_node.map_def(|&did| Some(def_path_hashes.hash(did)))
+                                                .unwrap();
+                               (item_dep_node, item_hash)
+                           })
+                           .collect();
+            item_hashes.sort(); // avoid artificial dependencies on item ordering
+            item_hashes.hash(&mut crate_state);
         }
 
-        // FIXME (#14132): This hash is still sensitive to e.g. the
-        // spans of the crate Attributes and their underlying
-        // MetaItems; we should make ContentHashable impl for those
-        // types and then use hash_content.  But, since all crate
-        // attributes should appear near beginning of the file, it is
-        // not such a big deal to be sensitive to their spans for now.
-        //
-        // We hash only the MetaItems instead of the entire Attribute
-        // to avoid hashing the AttrId
         for attr in &krate.attrs {
             debug!("krate attr {:?}", attr);
-            attr.meta().hash(&mut state);
+            attr.meta().hash(&mut crate_state);
         }
 
-        Svh::new(state.finish())
+        let crate_hash = crate_state.finish();
+        self.hashes.insert(DepNode::Krate, crate_hash);
+        debug!("calculate_crate_hash: crate_hash={:?}", crate_hash);
     }
+}
 
-    fn calculate_item_hash(self, def_id: DefId) -> u64 {
-        assert!(def_id.is_local());
-
-        debug!("calculate_item_hash(def_id={:?})", def_id);
-
-        let mut state = SipHasher::new();
-
-        {
-            let mut visit = StrictVersionHashVisitor::new(&mut state, self);
-            if def_id.index == CRATE_DEF_INDEX {
-                // the crate root itself is not registered in the map
-                // as an item, so we have to fetch it this way
-                let krate = self.map.krate();
-                intravisit::walk_crate(&mut visit, krate);
-            } else {
-                let node_id = self.map.as_local_node_id(def_id).unwrap();
-                match self.map.find(node_id) {
-                    Some(NodeItem(item)) => visit.visit_item(item),
-                    Some(NodeForeignItem(item)) => visit.visit_foreign_item(item),
-                    r => bug!("calculate_item_hash: expected an item for node {} not {:?}",
-                              node_id, r),
-                }
-            }
-        }
-
-        let hash = state.finish();
 
-        debug!("calculate_item_hash: def_id={:?} hash={:?}", def_id, hash);
+impl<'a, 'tcx> visit::Visitor<'tcx> for HashItemsVisitor<'a, 'tcx> {
+    fn visit_item(&mut self, item: &'tcx hir::Item) {
+        self.calculate_node_id(item.id, |v| v.visit_item(item));
+        visit::walk_item(self, item);
+    }
 
-        hash
+    fn visit_foreign_item(&mut self, item: &'tcx hir::ForeignItem) {
+        self.calculate_node_id(item.id, |v| v.visit_foreign_item(item));
+        visit::walk_foreign_item(self, item);
     }
 }
+
diff --git a/src/librustc_incremental/calculate_svh/svh_visitor.rs b/src/librustc_incremental/calculate_svh/svh_visitor.rs
index 42e7abeeaca..c1158dc2d5f 100644
--- a/src/librustc_incremental/calculate_svh/svh_visitor.rs
+++ b/src/librustc_incremental/calculate_svh/svh_visitor.rs
@@ -25,25 +25,30 @@ use rustc::hir::def::{Def, PathResolution};
 use rustc::hir::def_id::DefId;
 use rustc::hir::intravisit as visit;
 use rustc::hir::intravisit::{Visitor, FnKind};
-use rustc::hir::map::DefPath;
 use rustc::ty::TyCtxt;
 
 use std::hash::{Hash, SipHasher};
 
-pub struct StrictVersionHashVisitor<'a, 'tcx: 'a> {
-    pub tcx: TyCtxt<'a, 'tcx, 'tcx>,
+use super::def_path_hash::DefPathHashes;
+
+pub struct StrictVersionHashVisitor<'a, 'hash: 'a, 'tcx: 'hash> {
+    pub tcx: TyCtxt<'hash, 'tcx, 'tcx>,
     pub st: &'a mut SipHasher,
+
+    // collect a deterministic hash of def-ids that we have seen
+    def_path_hashes: &'a mut DefPathHashes<'hash, 'tcx>,
 }
 
-impl<'a, 'tcx> StrictVersionHashVisitor<'a, 'tcx> {
+impl<'a, 'hash, 'tcx> StrictVersionHashVisitor<'a, 'hash, 'tcx> {
     pub fn new(st: &'a mut SipHasher,
-               tcx: TyCtxt<'a, 'tcx, 'tcx>)
+               tcx: TyCtxt<'hash, 'tcx, 'tcx>,
+               def_path_hashes: &'a mut DefPathHashes<'hash, 'tcx>)
                -> Self {
-        StrictVersionHashVisitor { st: st, tcx: tcx }
+        StrictVersionHashVisitor { st: st, tcx: tcx, def_path_hashes: def_path_hashes }
     }
 
-    fn hash_def_path(&mut self, path: &DefPath) {
-        path.deterministic_hash_to(self.tcx, self.st);
+    fn compute_def_id_hash(&mut self, def_id: DefId) -> u64 {
+        self.def_path_hashes.hash(def_id)
     }
 }
 
@@ -187,20 +192,20 @@ pub enum SawStmtComponent {
     SawStmtSemi,
 }
 
-impl<'a, 'tcx> Visitor<'a> for StrictVersionHashVisitor<'a, 'tcx> {
+impl<'a, 'hash, 'tcx> Visitor<'tcx> for StrictVersionHashVisitor<'a, 'hash, 'tcx> {
     fn visit_nested_item(&mut self, _: ItemId) {
         // Each item is hashed independently; ignore nested items.
     }
 
-    fn visit_variant_data(&mut self, s: &'a VariantData, name: Name,
-                          g: &'a Generics, _: NodeId, _: Span) {
+    fn visit_variant_data(&mut self, s: &'tcx VariantData, name: Name,
+                          g: &'tcx Generics, _: NodeId, _: Span) {
         debug!("visit_variant_data: st={:?}", self.st);
         SawStructDef(name.as_str()).hash(self.st);
         visit::walk_generics(self, g);
         visit::walk_struct_def(self, s)
     }
 
-    fn visit_variant(&mut self, v: &'a Variant, g: &'a Generics, item_id: NodeId) {
+    fn visit_variant(&mut self, v: &'tcx Variant, g: &'tcx Generics, item_id: NodeId) {
         debug!("visit_variant: st={:?}", self.st);
         SawVariant.hash(self.st);
         // walk_variant does not call walk_generics, so do it here.
@@ -227,12 +232,12 @@ impl<'a, 'tcx> Visitor<'a> for StrictVersionHashVisitor<'a, 'tcx> {
         SawIdent(name.as_str()).hash(self.st);
     }
 
-    fn visit_lifetime(&mut self, l: &'a Lifetime) {
+    fn visit_lifetime(&mut self, l: &'tcx Lifetime) {
         debug!("visit_lifetime: st={:?}", self.st);
         SawLifetime(l.name.as_str()).hash(self.st);
     }
 
-    fn visit_lifetime_def(&mut self, l: &'a LifetimeDef) {
+    fn visit_lifetime_def(&mut self, l: &'tcx LifetimeDef) {
         debug!("visit_lifetime_def: st={:?}", self.st);
         SawLifetimeDef(l.lifetime.name.as_str()).hash(self.st);
     }
@@ -242,12 +247,12 @@ impl<'a, 'tcx> Visitor<'a> for StrictVersionHashVisitor<'a, 'tcx> {
     // monomorphization and cross-crate inlining generally implies
     // that a change to a crate body will require downstream
     // crates to be recompiled.
-    fn visit_expr(&mut self, ex: &'a Expr) {
+    fn visit_expr(&mut self, ex: &'tcx Expr) {
         debug!("visit_expr: st={:?}", self.st);
         SawExpr(saw_expr(&ex.node)).hash(self.st); visit::walk_expr(self, ex)
     }
 
-    fn visit_stmt(&mut self, s: &'a Stmt) {
+    fn visit_stmt(&mut self, s: &'tcx Stmt) {
         debug!("visit_stmt: st={:?}", self.st);
 
         // We don't want to modify the hash for decls, because
@@ -265,7 +270,7 @@ impl<'a, 'tcx> Visitor<'a> for StrictVersionHashVisitor<'a, 'tcx> {
         visit::walk_stmt(self, s)
     }
 
-    fn visit_foreign_item(&mut self, i: &'a ForeignItem) {
+    fn visit_foreign_item(&mut self, i: &'tcx ForeignItem) {
         debug!("visit_foreign_item: st={:?}", self.st);
 
         // FIXME (#14132) ideally we would incorporate privacy (or
@@ -275,7 +280,7 @@ impl<'a, 'tcx> Visitor<'a> for StrictVersionHashVisitor<'a, 'tcx> {
         SawForeignItem.hash(self.st); visit::walk_foreign_item(self, i)
     }
 
-    fn visit_item(&mut self, i: &'a Item) {
+    fn visit_item(&mut self, i: &'tcx Item) {
         debug!("visit_item: {:?} st={:?}", i, self.st);
 
         // FIXME (#14132) ideally would incorporate reachability
@@ -285,63 +290,63 @@ impl<'a, 'tcx> Visitor<'a> for StrictVersionHashVisitor<'a, 'tcx> {
         SawItem.hash(self.st); visit::walk_item(self, i)
     }
 
-    fn visit_mod(&mut self, m: &'a Mod, _s: Span, n: NodeId) {
+    fn visit_mod(&mut self, m: &'tcx Mod, _s: Span, n: NodeId) {
         debug!("visit_mod: st={:?}", self.st);
         SawMod.hash(self.st); visit::walk_mod(self, m, n)
     }
 
-    fn visit_ty(&mut self, t: &'a Ty) {
+    fn visit_ty(&mut self, t: &'tcx Ty) {
         debug!("visit_ty: st={:?}", self.st);
         SawTy.hash(self.st); visit::walk_ty(self, t)
     }
 
-    fn visit_generics(&mut self, g: &'a Generics) {
+    fn visit_generics(&mut self, g: &'tcx Generics) {
         debug!("visit_generics: st={:?}", self.st);
         SawGenerics.hash(self.st); visit::walk_generics(self, g)
     }
 
-    fn visit_fn(&mut self, fk: FnKind<'a>, fd: &'a FnDecl,
-                b: &'a Block, s: Span, n: NodeId) {
+    fn visit_fn(&mut self, fk: FnKind<'tcx>, fd: &'tcx FnDecl,
+                b: &'tcx Block, s: Span, n: NodeId) {
         debug!("visit_fn: st={:?}", self.st);
         SawFn.hash(self.st); visit::walk_fn(self, fk, fd, b, s, n)
     }
 
-    fn visit_trait_item(&mut self, ti: &'a TraitItem) {
+    fn visit_trait_item(&mut self, ti: &'tcx TraitItem) {
         debug!("visit_trait_item: st={:?}", self.st);
         SawTraitItem.hash(self.st); visit::walk_trait_item(self, ti)
     }
 
-    fn visit_impl_item(&mut self, ii: &'a ImplItem) {
+    fn visit_impl_item(&mut self, ii: &'tcx ImplItem) {
         debug!("visit_impl_item: st={:?}", self.st);
         SawImplItem.hash(self.st); visit::walk_impl_item(self, ii)
     }
 
-    fn visit_struct_field(&mut self, s: &'a StructField) {
+    fn visit_struct_field(&mut self, s: &'tcx StructField) {
         debug!("visit_struct_field: st={:?}", self.st);
         SawStructField.hash(self.st); visit::walk_struct_field(self, s)
     }
 
-    fn visit_path(&mut self, path: &'a Path, _: ast::NodeId) {
+    fn visit_path(&mut self, path: &'tcx Path, _: ast::NodeId) {
         debug!("visit_path: st={:?}", self.st);
         SawPath.hash(self.st); visit::walk_path(self, path)
     }
 
-    fn visit_block(&mut self, b: &'a Block) {
+    fn visit_block(&mut self, b: &'tcx Block) {
         debug!("visit_block: st={:?}", self.st);
         SawBlock.hash(self.st); visit::walk_block(self, b)
     }
 
-    fn visit_pat(&mut self, p: &'a Pat) {
+    fn visit_pat(&mut self, p: &'tcx Pat) {
         debug!("visit_pat: st={:?}", self.st);
         SawPat.hash(self.st); visit::walk_pat(self, p)
     }
 
-    fn visit_local(&mut self, l: &'a Local) {
+    fn visit_local(&mut self, l: &'tcx Local) {
         debug!("visit_local: st={:?}", self.st);
         SawLocal.hash(self.st); visit::walk_local(self, l)
     }
 
-    fn visit_arm(&mut self, a: &'a Arm) {
+    fn visit_arm(&mut self, a: &'tcx Arm) {
         debug!("visit_arm: st={:?}", self.st);
         SawArm.hash(self.st); visit::walk_arm(self, a)
     }
@@ -361,7 +366,7 @@ pub enum DefHash {
     SawErr,
 }
 
-impl<'a, 'tcx> StrictVersionHashVisitor<'a, 'tcx> {
+impl<'a, 'hash, 'tcx> StrictVersionHashVisitor<'a, 'hash, 'tcx> {
     fn hash_resolve(&mut self, id: ast::NodeId) {
         // Because whether or not a given id has an entry is dependent
         // solely on expr variant etc, we don't need to hash whether
@@ -369,20 +374,29 @@ impl<'a, 'tcx> StrictVersionHashVisitor<'a, 'tcx> {
         // variant it is above when we visit the HIR).
 
         if let Some(def) = self.tcx.def_map.borrow().get(&id) {
+            debug!("hash_resolve: id={:?} def={:?} st={:?}", id, def, self.st);
             self.hash_partial_def(def);
         }
 
         if let Some(traits) = self.tcx.trait_map.get(&id) {
+            debug!("hash_resolve: id={:?} traits={:?} st={:?}", id, traits, self.st);
             traits.len().hash(self.st);
-            for candidate in traits {
-                self.hash_def_id(candidate.def_id);
-            }
+
+            // The ordering of the candidates is not fixed. So we hash
+            // the def-ids and then sort them and hash the collection.
+            let mut candidates: Vec<_> =
+                traits.iter()
+                      .map(|&TraitCandidate { def_id, import_id: _ }| {
+                          self.compute_def_id_hash(def_id)
+                      })
+                      .collect();
+            candidates.sort();
+            candidates.hash(self.st);
         }
     }
 
     fn hash_def_id(&mut self, def_id: DefId) {
-        let def_path = self.tcx.def_path(def_id);
-        self.hash_def_path(&def_path);
+        self.compute_def_id_hash(def_id).hash(self.st);
     }
 
     fn hash_partial_def(&mut self, def: &PathResolution) {
diff --git a/src/librustc_incremental/lib.rs b/src/librustc_incremental/lib.rs
index 0d11b0794fe..d31d97b22cf 100644
--- a/src/librustc_incremental/lib.rs
+++ b/src/librustc_incremental/lib.rs
@@ -38,7 +38,8 @@ mod calculate_svh;
 mod persist;
 
 pub use assert_dep_graph::assert_dep_graph;
-pub use calculate_svh::SvhCalculate;
+pub use calculate_svh::compute_incremental_hashes_map;
+pub use calculate_svh::IncrementalHashesMap;
 pub use persist::load_dep_graph;
 pub use persist::save_dep_graph;
 pub use persist::save_trans_partition;
diff --git a/src/librustc_incremental/persist/dirty_clean.rs b/src/librustc_incremental/persist/dirty_clean.rs
index 3c77cc07d3d..65da3a09ecc 100644
--- a/src/librustc_incremental/persist/dirty_clean.rs
+++ b/src/librustc_incremental/persist/dirty_clean.rs
@@ -133,6 +133,7 @@ impl<'a, 'tcx> DirtyCleanVisitor<'a, 'tcx> {
         debug!("assert_dirty({:?})", dep_node);
 
         match dep_node {
+            DepNode::Krate |
             DepNode::Hir(_) => {
                 // HIR nodes are inputs, so if we are asserting that the HIR node is
                 // dirty, we check the dirty input set.
@@ -161,6 +162,7 @@ impl<'a, 'tcx> DirtyCleanVisitor<'a, 'tcx> {
         debug!("assert_clean({:?})", dep_node);
 
         match dep_node {
+            DepNode::Krate |
             DepNode::Hir(_) => {
                 // For HIR nodes, check the inputs.
                 if self.dirty_inputs.contains(&dep_node) {
diff --git a/src/librustc_incremental/persist/hash.rs b/src/librustc_incremental/persist/hash.rs
index 344b05f0954..5d01f880602 100644
--- a/src/librustc_incremental/persist/hash.rs
+++ b/src/librustc_incremental/persist/hash.rs
@@ -8,7 +8,6 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-use calculate_svh::SvhCalculate;
 use rbml::Error;
 use rbml::opaque::Decoder;
 use rustc::dep_graph::DepNode;
@@ -21,19 +20,24 @@ use std::io::{ErrorKind, Read};
 use std::fs::File;
 use syntax::ast;
 
+use IncrementalHashesMap;
 use super::data::*;
 use super::util::*;
 
 pub struct HashContext<'a, 'tcx: 'a> {
     pub tcx: TyCtxt<'a, 'tcx, 'tcx>,
+    incremental_hashes_map: &'a IncrementalHashesMap,
     item_metadata_hashes: FnvHashMap<DefId, u64>,
     crate_hashes: FnvHashMap<ast::CrateNum, Svh>,
 }
 
 impl<'a, 'tcx> HashContext<'a, 'tcx> {
-    pub fn new(tcx: TyCtxt<'a, 'tcx, 'tcx>) -> Self {
+    pub fn new(tcx: TyCtxt<'a, 'tcx, 'tcx>,
+               incremental_hashes_map: &'a IncrementalHashesMap)
+               -> Self {
         HashContext {
             tcx: tcx,
+            incremental_hashes_map: incremental_hashes_map,
             item_metadata_hashes: FnvHashMap(),
             crate_hashes: FnvHashMap(),
         }
@@ -41,17 +45,32 @@ impl<'a, 'tcx> HashContext<'a, 'tcx> {
 
     pub fn is_hashable(dep_node: &DepNode<DefId>) -> bool {
         match *dep_node {
+            DepNode::Krate |
             DepNode::Hir(_) => true,
             DepNode::MetaData(def_id) => !def_id.is_local(),
             _ => false,
         }
     }
 
-    pub fn hash(&mut self, dep_node: &DepNode<DefId>) -> Option<(DefId, u64)> {
+    pub fn hash(&mut self, dep_node: &DepNode<DefId>) -> Option<u64> {
         match *dep_node {
+            DepNode::Krate => {
+                Some(self.incremental_hashes_map[dep_node])
+            }
+
             // HIR nodes (which always come from our crate) are an input:
             DepNode::Hir(def_id) => {
-                Some((def_id, self.hir_hash(def_id)))
+                assert!(def_id.is_local(),
+                        "cannot hash HIR for non-local def-id {:?} => {:?}",
+                        def_id,
+                        self.tcx.item_path_str(def_id));
+
+                assert!(!self.tcx.map.is_inlined_def_id(def_id),
+                        "cannot hash HIR for inlined def-id {:?} => {:?}",
+                        def_id,
+                        self.tcx.item_path_str(def_id));
+
+                Some(self.incremental_hashes_map[dep_node])
             }
 
             // MetaData from other crates is an *input* to us.
@@ -59,7 +78,7 @@ impl<'a, 'tcx> HashContext<'a, 'tcx> {
             // don't hash them, but we do compute a hash for them and
             // save it for others to use.
             DepNode::MetaData(def_id) if !def_id.is_local() => {
-                Some((def_id, self.metadata_hash(def_id)))
+                Some(self.metadata_hash(def_id))
             }
 
             _ => {
@@ -72,21 +91,6 @@ impl<'a, 'tcx> HashContext<'a, 'tcx> {
         }
     }
 
-    fn hir_hash(&mut self, def_id: DefId) -> u64 {
-        assert!(def_id.is_local(),
-                "cannot hash HIR for non-local def-id {:?} => {:?}",
-                def_id,
-                self.tcx.item_path_str(def_id));
-
-        assert!(!self.tcx.map.is_inlined_def_id(def_id),
-                "cannot hash HIR for inlined def-id {:?} => {:?}",
-                def_id,
-                self.tcx.item_path_str(def_id));
-
-        // FIXME(#32753) -- should we use a distinct hash here
-        self.tcx.calculate_item_hash(def_id)
-    }
-
     fn metadata_hash(&mut self, def_id: DefId) -> u64 {
         debug!("metadata_hash(def_id={:?})", def_id);
 
diff --git a/src/librustc_incremental/persist/load.rs b/src/librustc_incremental/persist/load.rs
index c736437df1a..75448d199f7 100644
--- a/src/librustc_incremental/persist/load.rs
+++ b/src/librustc_incremental/persist/load.rs
@@ -22,6 +22,7 @@ use std::io::Read;
 use std::fs::{self, File};
 use std::path::{Path};
 
+use IncrementalHashesMap;
 use super::data::*;
 use super::directory::*;
 use super::dirty_clean;
@@ -38,16 +39,18 @@ type CleanEdges = Vec<(DepNode<DefId>, DepNode<DefId>)>;
 /// early in compilation, before we've really done any work, but
 /// actually it doesn't matter all that much.) See `README.md` for
 /// more general overview.
-pub fn load_dep_graph<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>) {
+pub fn load_dep_graph<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
+                                incremental_hashes_map: &IncrementalHashesMap) {
     if tcx.sess.opts.incremental.is_none() {
         return;
     }
 
     let _ignore = tcx.dep_graph.in_ignore();
-    load_dep_graph_if_exists(tcx);
+    load_dep_graph_if_exists(tcx, incremental_hashes_map);
 }
 
-fn load_dep_graph_if_exists<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>) {
+fn load_dep_graph_if_exists<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
+                                      incremental_hashes_map: &IncrementalHashesMap) {
     let dep_graph_path = dep_graph_path(tcx).unwrap();
     let dep_graph_data = match load_data(tcx.sess, &dep_graph_path) {
         Some(p) => p,
@@ -60,7 +63,7 @@ fn load_dep_graph_if_exists<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>) {
         None => return // no file
     };
 
-    match decode_dep_graph(tcx, &dep_graph_data, &work_products_data) {
+    match decode_dep_graph(tcx, incremental_hashes_map, &dep_graph_data, &work_products_data) {
         Ok(dirty_nodes) => dirty_nodes,
         Err(err) => {
             tcx.sess.warn(
@@ -97,6 +100,7 @@ fn load_data(sess: &Session, path: &Path) -> Option<Vec<u8>> {
 /// Decode the dep graph and load the edges/nodes that are still clean
 /// into `tcx.dep_graph`.
 pub fn decode_dep_graph<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
+                                  incremental_hashes_map: &IncrementalHashesMap,
                                   dep_graph_data: &[u8],
                                   work_products_data: &[u8])
                                   -> Result<(), Error>
@@ -133,7 +137,10 @@ pub fn decode_dep_graph<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
     // reason for this is that this way we can include nodes that have
     // been removed (which no longer have a `DefId` in the current
     // compilation).
-    let dirty_raw_source_nodes = dirty_nodes(tcx, &serialized_dep_graph.hashes, &retraced);
+    let dirty_raw_source_nodes = dirty_nodes(tcx,
+                                             incremental_hashes_map,
+                                             &serialized_dep_graph.hashes,
+                                             &retraced);
 
     // Create a list of (raw-source-node ->
     // retracted-target-node) edges. In the process of retracing the
@@ -206,15 +213,16 @@ pub fn decode_dep_graph<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 /// Computes which of the original set of def-ids are dirty. Stored in
 /// a bit vector where the index is the DefPathIndex.
 fn dirty_nodes<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
-                         hashes: &[SerializedHash],
+                         incremental_hashes_map: &IncrementalHashesMap,
+                         serialized_hashes: &[SerializedHash],
                          retraced: &RetracedDefIdDirectory)
                          -> DirtyNodes {
-    let mut hcx = HashContext::new(tcx);
+    let mut hcx = HashContext::new(tcx, incremental_hashes_map);
     let mut dirty_nodes = FnvHashSet();
 
-    for hash in hashes {
+    for hash in serialized_hashes {
         if let Some(dep_node) = retraced.map(&hash.dep_node) {
-            let (_, current_hash) = hcx.hash(&dep_node).unwrap();
+            let current_hash = hcx.hash(&dep_node).unwrap();
             if current_hash == hash.hash {
                 continue;
             }
diff --git a/src/librustc_incremental/persist/preds.rs b/src/librustc_incremental/persist/preds.rs
index a82951afcb1..af13484e428 100644
--- a/src/librustc_incremental/persist/preds.rs
+++ b/src/librustc_incremental/persist/preds.rs
@@ -62,7 +62,7 @@ impl<'q> Predecessors<'q> {
         let mut hashes = FnvHashMap();
         for input in inputs.values().flat_map(|v| v.iter().cloned()) {
             hashes.entry(input)
-                  .or_insert_with(|| hcx.hash(input).unwrap().1);
+                  .or_insert_with(|| hcx.hash(input).unwrap());
         }
 
         Predecessors {
diff --git a/src/librustc_incremental/persist/save.rs b/src/librustc_incremental/persist/save.rs
index a9523a81fba..74ee876d0bb 100644
--- a/src/librustc_incremental/persist/save.rs
+++ b/src/librustc_incremental/persist/save.rs
@@ -21,20 +21,22 @@ use std::io::{self, Cursor, Write};
 use std::fs::{self, File};
 use std::path::PathBuf;
 
+use IncrementalHashesMap;
 use super::data::*;
 use super::directory::*;
 use super::hash::*;
 use super::preds::*;
 use super::util::*;
 
-pub fn save_dep_graph<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>) {
+pub fn save_dep_graph<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
+                                incremental_hashes_map: &IncrementalHashesMap) {
     debug!("save_dep_graph()");
     let _ignore = tcx.dep_graph.in_ignore();
     let sess = tcx.sess;
     if sess.opts.incremental.is_none() {
         return;
     }
-    let mut hcx = HashContext::new(tcx);
+    let mut hcx = HashContext::new(tcx, incremental_hashes_map);
     let mut builder = DefIdDirectoryBuilder::new(tcx);
     let query = tcx.dep_graph.query();
     let preds = Predecessors::new(&query, &mut hcx);
diff --git a/src/librustc_trans/back/link.rs b/src/librustc_trans/back/link.rs
index 68a176a3781..9f401b13d6f 100644
--- a/src/librustc_trans/back/link.rs
+++ b/src/librustc_trans/back/link.rs
@@ -26,10 +26,10 @@ use CrateTranslation;
 use util::common::time;
 use util::fs::fix_windows_verbatim_for_gcc;
 use rustc::dep_graph::DepNode;
-use rustc::ty::TyCtxt;
+use rustc::hir::svh::Svh;
 use rustc_back::tempdir::TempDir;
+use rustc_incremental::IncrementalHashesMap;
 
-use rustc_incremental::SvhCalculate;
 use std::ascii;
 use std::char;
 use std::env;
@@ -125,12 +125,12 @@ pub fn find_crate_name(sess: Option<&Session>,
 
 }
 
-pub fn build_link_meta<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
-                                 name: &str)
-                                 -> LinkMeta {
+pub fn build_link_meta(incremental_hashes_map: &IncrementalHashesMap,
+                       name: &str)
+                       -> LinkMeta {
     let r = LinkMeta {
         crate_name: name.to_owned(),
-        crate_hash: tcx.calculate_krate_hash(),
+        crate_hash: Svh::new(incremental_hashes_map[&DepNode::Krate]),
     };
     info!("{:?}", r);
     return r;
diff --git a/src/librustc_trans/base.rs b/src/librustc_trans/base.rs
index f190fbeb6fe..cab353cd262 100644
--- a/src/librustc_trans/base.rs
+++ b/src/librustc_trans/base.rs
@@ -48,6 +48,7 @@ use rustc::hir::map as hir_map;
 use rustc::util::common::time;
 use rustc::mir::mir_map::MirMap;
 use rustc_data_structures::graph::OUTGOING;
+use rustc_incremental::IncrementalHashesMap;
 use session::config::{self, NoDebugInfo, FullDebugInfo};
 use session::Session;
 use _match;
@@ -2481,7 +2482,8 @@ pub fn filter_reachable_ids(tcx: TyCtxt, reachable: NodeSet) -> NodeSet {
 
 pub fn trans_crate<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                              mir_map: &MirMap<'tcx>,
-                             analysis: ty::CrateAnalysis)
+                             analysis: ty::CrateAnalysis,
+                             incremental_hashes_map: &IncrementalHashesMap)
                              -> CrateTranslation {
     let _task = tcx.dep_graph.in_task(DepNode::TransCrate);
 
@@ -2506,7 +2508,7 @@ pub fn trans_crate<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
         tcx.sess.opts.debug_assertions
     };
 
-    let link_meta = link::build_link_meta(tcx, name);
+    let link_meta = link::build_link_meta(incremental_hashes_map, name);
 
     let shared_ccx = SharedCrateContext::new(tcx,
                                              &mir_map,
diff --git a/src/librustdoc/core.rs b/src/librustdoc/core.rs
index 10736d2c827..8032b5c3104 100644
--- a/src/librustdoc/core.rs
+++ b/src/librustdoc/core.rs
@@ -159,7 +159,7 @@ pub fn run_core(search_paths: SearchPaths,
                                                      resolutions,
                                                      &arenas,
                                                      &name,
-                                                     |tcx, _, analysis, result| {
+                                                     |tcx, _, analysis, _, result| {
         if let Err(_) = result {
             sess.fatal("Compilation failed, aborting rustdoc");
         }
diff --git a/src/test/incremental/crate_hash_reorder.rs b/src/test/incremental/crate_hash_reorder.rs
new file mode 100644
index 00000000000..3f1bdb7e3c6
--- /dev/null
+++ b/src/test/incremental/crate_hash_reorder.rs
@@ -0,0 +1,39 @@
+// Copyright 2014 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.
+
+// Test that the crate hash is not affected by reordering items.
+
+// revisions:rpass1 rpass2 rpass3
+// compile-flags: -Z query-dep-graph
+
+#![feature(rustc_attrs)]
+
+// Check that reordering otherwise identical items is not considered a
+// change at all.
+#[rustc_clean(label="Krate", cfg="rpass2")]
+
+// But removing an item, naturally, is.
+#[rustc_dirty(label="Krate", cfg="rpass3")]
+
+#[cfg(rpass1)]
+pub struct X {
+    pub x: u32,
+}
+
+pub struct Y {
+    pub x: u32,
+}
+
+#[cfg(rpass2)]
+pub struct X {
+    pub x: u32,
+}
+
+pub fn main() { }
diff --git a/src/test/incremental/issue-35593.rs b/src/test/incremental/issue-35593.rs
new file mode 100644
index 00000000000..51e04dd7b2c
--- /dev/null
+++ b/src/test/incremental/issue-35593.rs
@@ -0,0 +1,21 @@
+// Copyright 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.
+
+// Regression test for #35593. Check that we can reuse this trivially
+// equal example.
+
+// revisions:rpass1 rpass2
+
+#![feature(rustc_attrs)]
+#![rustc_partition_reused(module="issue_35593", cfg="rpass2")]
+
+fn main() {
+    println!("hello world");
+}
diff --git a/src/test/incremental/string_constant.rs b/src/test/incremental/string_constant.rs
index 72072248ec0..ba8d3cc934b 100644
--- a/src/test/incremental/string_constant.rs
+++ b/src/test/incremental/string_constant.rs
@@ -17,10 +17,6 @@
 // Here the only thing which changes is the string constant in `x`.
 // Therefore, the compiler deduces (correctly) that typeck is not
 // needed even for callers of `x`.
-//
-// It is not entirely clear why `TransCrateItem` invalidates `y` and
-// `z`, actually, I think it's because of the structure of
-// trans. -nmatsakis
 
 fn main() { }
 
@@ -41,10 +37,8 @@ mod x {
 mod y {
     use x;
 
-    // FIXME(#35078) -- when body of `x` changes, we treat it as
-    // though signature changed.
-    #[rustc_dirty(label="TypeckItemBody", cfg="rpass2")]
-    #[rustc_dirty(label="TransCrateItem", cfg="rpass2")]
+    #[rustc_clean(label="TypeckItemBody", cfg="rpass2")]
+    #[rustc_clean(label="TransCrateItem", cfg="rpass2")]
     pub fn y() {
         x::x();
     }