incr.comp.: Precompute small hash for filenames to save some work.

src/librustc/ich/hcx.rs

@@ -341,7 +341,7 @@ impl<'gcx> HashStable<StableHashingContext<'gcx>> for Span {
         std_hash::Hash::hash(&TAG_VALID_SPAN, hasher);
         // We truncate the stable_id hash and line and col numbers. The chances
         // of causing a collision this way should be minimal.
-        std_hash::Hash::hash(&file_lo.name, hasher);
+        std_hash::Hash::hash(&(file_lo.name_hash as u64), hasher);
 
         let col = (col_lo.0 as u64) & 0xFF;
         let line = ((line_lo as u64) & 0xFF_FF_FF) << 8;

src/librustc/ich/impls_syntax.rs

@@ -387,7 +387,8 @@ impl<'gcx> HashStable<StableHashingContext<'gcx>> for FileMap {
                                           hcx: &mut StableHashingContext<'gcx>,
                                           hasher: &mut StableHasher<W>) {
         let FileMap {
-            ref name,
+            name: _, // We hash the smaller name_hash instead of this
+            name_hash,
             name_was_remapped,
             unmapped_path: _,
             crate_of_origin,
@@ -402,7 +403,7 @@ impl<'gcx> HashStable<StableHashingContext<'gcx>> for FileMap {
             ref non_narrow_chars,
         } = *self;
 
-        name.hash_stable(hcx, hasher);
+        (name_hash as u64).hash_stable(hcx, hasher);
         name_was_remapped.hash_stable(hcx, hasher);
 
         DefId {

src/librustc_metadata/decoder.rs

@@ -1129,6 +1129,7 @@ impl<'a, 'tcx> CrateMetadata {
                                       lines,
                                       multibyte_chars,
                                       non_narrow_chars,
+                                      name_hash,
                                       .. } = filemap_to_import;
 
             let source_length = (end_pos - start_pos).to_usize();
@@ -1155,6 +1156,7 @@ impl<'a, 'tcx> CrateMetadata {
                                                                    name_was_remapped,
                                                                    self.cnum.as_u32(),
                                                                    src_hash,
+                                                                   name_hash,
                                                                    source_length,
                                                                    lines,
                                                                    multibyte_chars,

src/librustc_metadata/encoder.rs

@@ -28,8 +28,10 @@ use rustc::ty::codec::{self as ty_codec, TyEncoder};
 use rustc::session::config::{self, CrateTypeProcMacro};
 use rustc::util::nodemap::{FxHashMap, NodeSet};
 
+use rustc_data_structures::stable_hasher::StableHasher;
 use rustc_serialize::{Encodable, Encoder, SpecializedEncoder, opaque};
 
+use std::hash::Hash;
 use std::io::prelude::*;
 use std::io::Cursor;
 use std::path::Path;
@@ -290,6 +292,11 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
                         } else {
                             let mut adapted = (**filemap).clone();
                             adapted.name = Path::new(&working_dir).join(name).into();
+                            adapted.name_hash = {
+                                let mut hasher: StableHasher<u128> = StableHasher::new();
+                                adapted.name.hash(&mut hasher);
+                                hasher.finish()
+                            };
                             Rc::new(adapted)
                         }
                     },

src/libsyntax/codemap.rs

@@ -246,6 +246,7 @@ impl CodeMap {
                                 name_was_remapped: bool,
                                 crate_of_origin: u32,
                                 src_hash: u128,
+                                name_hash: u128,
                                 source_len: usize,
                                 mut file_local_lines: Vec<BytePos>,
                                 mut file_local_multibyte_chars: Vec<MultiByteChar>,
@@ -282,6 +283,7 @@ impl CodeMap {
             lines: RefCell::new(file_local_lines),
             multibyte_chars: RefCell::new(file_local_multibyte_chars),
             non_narrow_chars: RefCell::new(file_local_non_narrow_chars),
+            name_hash,
         });
 
         files.push(filemap.clone());

src/libsyntax_pos/lib.rs

@@ -30,7 +30,7 @@ use std::borrow::Cow;
 use std::cell::{Cell, RefCell};
 use std::cmp::{self, Ordering};
 use std::fmt;
-use std::hash::Hasher;
+use std::hash::{Hasher, Hash};
 use std::ops::{Add, Sub};
 use std::path::PathBuf;
 use std::rc::Rc;
@@ -691,6 +691,8 @@ pub struct FileMap {
     pub multibyte_chars: RefCell<Vec<MultiByteChar>>,
     /// Width of characters that are not narrow in the source code
     pub non_narrow_chars: RefCell<Vec<NonNarrowChar>>,
+    /// A hash of the filename, used for speeding up the incr. comp. hashing.
+    pub name_hash: u128,
 }
 
 impl Encodable for FileMap {
@@ -752,6 +754,9 @@ impl Encodable for FileMap {
             })?;
             s.emit_struct_field("non_narrow_chars", 8, |s| {
                 (*self.non_narrow_chars.borrow()).encode(s)
+            })?;
+            s.emit_struct_field("name_hash", 9, |s| {
+                self.name_hash.encode(s)
             })
         })
     }
@@ -801,6 +806,8 @@ impl Decodable for FileMap {
                 d.read_struct_field("multibyte_chars", 7, |d| Decodable::decode(d))?;
             let non_narrow_chars: Vec<NonNarrowChar> =
                 d.read_struct_field("non_narrow_chars", 8, |d| Decodable::decode(d))?;
+            let name_hash: u128 =
+                d.read_struct_field("name_hash", 9, |d| Decodable::decode(d))?;
             Ok(FileMap {
                 name,
                 name_was_remapped,
@@ -816,7 +823,8 @@ impl Decodable for FileMap {
                 external_src: RefCell::new(ExternalSource::AbsentOk),
                 lines: RefCell::new(lines),
                 multibyte_chars: RefCell::new(multibyte_chars),
-                non_narrow_chars: RefCell::new(non_narrow_chars)
+                non_narrow_chars: RefCell::new(non_narrow_chars),
+                name_hash,
             })
         })
     }
@@ -836,9 +844,16 @@ impl FileMap {
                start_pos: BytePos) -> FileMap {
         remove_bom(&mut src);
 
-        let mut hasher: StableHasher<u128> = StableHasher::new();
-        hasher.write(src.as_bytes());
-        let src_hash = hasher.finish();
+        let src_hash = {
+            let mut hasher: StableHasher<u128> = StableHasher::new();
+            hasher.write(src.as_bytes());
+            hasher.finish()
+        };
+        let name_hash = {
+            let mut hasher: StableHasher<u128> = StableHasher::new();
+            name.hash(&mut hasher);
+            hasher.finish()
+        };
         let end_pos = start_pos.to_usize() + src.len();
 
         FileMap {
@@ -854,6 +869,7 @@ impl FileMap {
             lines: RefCell::new(Vec::new()),
             multibyte_chars: RefCell::new(Vec::new()),
             non_narrow_chars: RefCell::new(Vec::new()),
+            name_hash,
         }
     }