Make metadata encoding deterministic

`ty::Predicate` was being used as a key for a hash map, but its hash
implementation indirectly hashed addresses, which vary between each
compiler run. This is fixed by sorting predicates by their ID before
encoding them.

In my tests, rustc is now able to produce deterministic results when
compiling libcore and libstd.

I've beefed up `run-make/reproducible-build` to compare the produced
artifacts bit-by-bit. This doesn't catch everything, but should be a
good start.

cc #34902

Author: jonas-schievink

src/librustc_metadata/encoder.rs

@@ -862,8 +862,13 @@ fn encode_xrefs<'a, 'tcx>(ecx: &EncodeContext<'a, 'tcx>,
                           xrefs: FnvHashMap<XRef<'tcx>, u32>)
 {
     let mut xref_positions = vec![0; xrefs.len()];
+
+    // Encode XRefs sorted by their ID
+    let mut sorted_xrefs: Vec<_> = xrefs.into_iter().collect();
+    sorted_xrefs.sort_by_key(|&(_, id)| id);
+
     rbml_w.start_tag(tag_xref_data);
-    for (xref, id) in xrefs.into_iter() {
+    for (xref, id) in sorted_xrefs.into_iter() {
         xref_positions[id as usize] = rbml_w.mark_stable_position() as u32;
         match xref {
             XRef::Predicate(p) => {

src/test/run-make/reproducible-build/Makefile

@@ -1,20 +1,24 @@
 -include ../tools.mk
 all:
 	$(RUSTC) reproducible-build-aux.rs
+	mv libreproducible_build_aux.rlib first.rlib
+	$(RUSTC) reproducible-build-aux.rs
+	cp libreproducible_build_aux.rlib second.rlib
+	cmp "first.rlib" "second.rlib" || exit 1
 	$(RUSTC) reproducible-build.rs -o"$(TMPDIR)/reproducible-build1"
 	$(RUSTC) reproducible-build.rs -o"$(TMPDIR)/reproducible-build2"
-	nm "$(TMPDIR)/reproducible-build1" | sort > "$(TMPDIR)/reproducible-build1.nm"
-	nm "$(TMPDIR)/reproducible-build2" | sort > "$(TMPDIR)/reproducible-build2.nm"
-	cmp "$(TMPDIR)/reproducible-build1.nm" "$(TMPDIR)/reproducible-build2.nm" || exit 1
+	cmp "$(TMPDIR)/reproducible-build1" "$(TMPDIR)/reproducible-build2" || exit 1
+	$(RUSTC) reproducible-build-aux.rs -g
+	mv libreproducible_build_aux.rlib first.rlib
 	$(RUSTC) reproducible-build-aux.rs -g
+	cp libreproducible_build_aux.rlib second.rlib
 	$(RUSTC) reproducible-build.rs -g -o"$(TMPDIR)/reproducible-build1-debug"
 	$(RUSTC) reproducible-build.rs -g -o"$(TMPDIR)/reproducible-build2-debug"
-	nm "$(TMPDIR)/reproducible-build1-debug" | sort > "$(TMPDIR)/reproducible-build1-debug.nm"
-	nm "$(TMPDIR)/reproducible-build2-debug" | sort > "$(TMPDIR)/reproducible-build2-debug.nm"
-	cmp "$(TMPDIR)/reproducible-build1-debug.nm" "$(TMPDIR)/reproducible-build2-debug.nm" || exit 1
+	cmp "$(TMPDIR)/reproducible-build1-debug" "$(TMPDIR)/reproducible-build2-debug" || exit 1
+	$(RUSTC) reproducible-build-aux.rs -O
+	mv libreproducible_build_aux.rlib first.rlib
 	$(RUSTC) reproducible-build-aux.rs -O
+	cp libreproducible_build_aux.rlib second.rlib
 	$(RUSTC) reproducible-build.rs -O -o"$(TMPDIR)/reproducible-build1-opt"
 	$(RUSTC) reproducible-build.rs -O -o"$(TMPDIR)/reproducible-build2-opt"
-	nm "$(TMPDIR)/reproducible-build1-opt" | sort > "$(TMPDIR)/reproducible-build1-opt.nm"
-	nm "$(TMPDIR)/reproducible-build2-opt" | sort > "$(TMPDIR)/reproducible-build2-opt.nm"
-	cmp "$(TMPDIR)/reproducible-build1-opt.nm" "$(TMPDIR)/reproducible-build2-opt.nm" || exit 1
+	cmp "$(TMPDIR)/reproducible-build1-opt" "$(TMPDIR)/reproducible-build2-opt" || exit 1

src/test/run-make/reproducible-build/reproducible-build-aux.rs

@@ -33,6 +33,12 @@ pub enum Enum {
 
 pub struct TupleStruct(pub i8, pub i16, pub i32, pub i64);
 
-pub trait Trait<T1, T2> {
+pub trait Marker {}
+impl Marker for char {}
+impl<T, U> Marker for (T, U) {}
+
+pub trait Trait<T1: Marker + Marker + Marker, T2> where T1: 'static {
+    type Assoc: Marker;
+
     fn foo(&self);
 }

src/test/run-make/reproducible-build/reproducible-build.rs

@@ -67,7 +67,9 @@ impl Trait<i32, u64> for u64 {
     fn foo(&self) {}
 }
 
-impl reproducible_build_aux::Trait<char, String> for TupleStruct {
+impl<T: reproducible_build_aux::Marker + 'static> reproducible_build_aux::Trait<T, String> for TupleStruct {
+    type Assoc = (u8, i16);
+
     fn foo(&self) {}
 }
 
@@ -117,12 +119,10 @@ fn main() {
     let _ = reproducible_build_aux::Enum::Variant3 { x: 0 };
     let _ = reproducible_build_aux::TupleStruct(1, 2, 3, 4);
 
-    let object_shim: &reproducible_build_aux::Trait<char, String> = &TupleStruct(0, 1, 2, 3);
+    let object_shim: &reproducible_build_aux::Trait<char, String, Assoc=(u8, i16)> = &TupleStruct(0, 1, 2, 3);
     object_shim.foo();
 
     let pointer_shim: &Fn(i32) = &regular_fn;
 
     TupleStruct(1, 2, 3, 4).bar();
 }
-
-