rustc: Implement ThinLTO

This commit is an implementation of LLVM's ThinLTO for consumption in rustc
itself. Currently today LTO works by merging all relevant LLVM modules into one
and then running optimization passes. "Thin" LTO operates differently by having
more sharded work and allowing parallelism opportunities between optimizing
codegen units. Further down the road Thin LTO also allows *incremental* LTO
which should enable even faster release builds without compromising on the
performance we have today.

This commit uses a `-Z thinlto` flag to gate whether ThinLTO is enabled. It then
also implements two forms of ThinLTO:

* In one mode we'll *only* perform ThinLTO over the codegen units produced in a
  single compilation. That is, we won't load upstream rlibs, but we'll instead
  just perform ThinLTO amongst all codegen units produced by the compiler for
  the local crate. This is intended to emulate a desired end point where we have
  codegen units turned on by default for all crates and ThinLTO allows us to do
  this without performance loss.

* In anther mode, like full LTO today, we'll optimize all upstream dependencies
  in "thin" mode. Unlike today, however, this LTO step is fully parallelized so
  should finish much more quickly.

There's a good bit of comments about what the implementation is doing and where
it came from, but the tl;dr; is that currently most of the support here is
copied from upstream LLVM. This code duplication is done for a number of
reasons:

* Controlling parallelism means we can use the existing jobserver support to
  avoid overloading machines.
* We will likely want a slightly different form of incremental caching which
  integrates with our own incremental strategy, but this is yet to be
  determined.
* This buys us some flexibility about when/where we run ThinLTO, as well as
  having it tailored to fit our needs for the time being.
* Finally this allows us to reuse some artifacts such as our `TargetMachine`
  creation, where all our options we used today aren't necessarily supported by
  upstream LLVM yet.

My hope is that we can get some experience with this copy/paste in tree and then
eventually upstream some work to LLVM itself to avoid the duplication while
still ensuring our needs are met. Otherwise I fear that maintaining these
bindings may be quite costly over the years with LLVM updates!

7 files changed, 30 insertions, 30 deletions

diff --git a/src/test/codegen-units/item-collection/drop_in_place_intrinsic.rs b/src/test/codegen-units/item-collection/drop_in_place_intrinsic.rs
index d8e6028b799..bd1325e7501 100644
--- a/src/test/codegen-units/item-collection/drop_in_place_intrinsic.rs
+++ b/src/test/codegen-units/item-collection/drop_in_place_intrinsic.rs
@@ -11,7 +11,7 @@
 // ignore-tidy-linelength
 // compile-flags:-Zprint-trans-items=eager
 
-//~ TRANS_ITEM fn core::ptr[0]::drop_in_place[0]<drop_in_place_intrinsic::StructWithDtor[0]> @@ drop_in_place_intrinsic.cgu-0[Internal]
+//~ TRANS_ITEM fn core::ptr[0]::drop_in_place[0]<drop_in_place_intrinsic::StructWithDtor[0]> @@ drop_in_place_intrinsic0[Internal]
 struct StructWithDtor(u32);
 
 impl Drop for StructWithDtor {
@@ -22,7 +22,7 @@ impl Drop for StructWithDtor {
 //~ TRANS_ITEM fn drop_in_place_intrinsic::main[0]
 fn main() {
 
-    //~ TRANS_ITEM fn core::ptr[0]::drop_in_place[0]<[drop_in_place_intrinsic::StructWithDtor[0]; 2]> @@ drop_in_place_intrinsic.cgu-0[Internal]
+    //~ TRANS_ITEM fn core::ptr[0]::drop_in_place[0]<[drop_in_place_intrinsic::StructWithDtor[0]; 2]> @@ drop_in_place_intrinsic0[Internal]
     let x = [StructWithDtor(0), StructWithDtor(1)];
 
     drop_slice_in_place(&x);
@@ -34,7 +34,7 @@ fn drop_slice_in_place(x: &[StructWithDtor]) {
         // This is the interesting thing in this test case: Normally we would
         // not have drop-glue for the unsized [StructWithDtor]. This has to be
         // generated though when the drop_in_place() intrinsic is used.
-        //~ TRANS_ITEM fn core::ptr[0]::drop_in_place[0]<[drop_in_place_intrinsic::StructWithDtor[0]]> @@ drop_in_place_intrinsic.cgu-0[Internal]
+        //~ TRANS_ITEM fn core::ptr[0]::drop_in_place[0]<[drop_in_place_intrinsic::StructWithDtor[0]]> @@ drop_in_place_intrinsic0[Internal]
         ::std::ptr::drop_in_place(x as *const _ as *mut [StructWithDtor]);
     }
 }
diff --git a/src/test/codegen-units/item-collection/generic-drop-glue.rs b/src/test/codegen-units/item-collection/generic-drop-glue.rs
index 06e02b10015..108a8b570de 100644
--- a/src/test/codegen-units/item-collection/generic-drop-glue.rs
+++ b/src/test/codegen-units/item-collection/generic-drop-glue.rs
@@ -45,7 +45,7 @@ enum EnumNoDrop<T1, T2> {
 struct NonGenericNoDrop(i32);
 
 struct NonGenericWithDrop(i32);
-//~ TRANS_ITEM fn core::ptr[0]::drop_in_place[0]<generic_drop_glue::NonGenericWithDrop[0]> @@ generic_drop_glue.cgu-0[Internal]
+//~ TRANS_ITEM fn core::ptr[0]::drop_in_place[0]<generic_drop_glue::NonGenericWithDrop[0]> @@ generic_drop_glue0[Internal]
 
 impl Drop for NonGenericWithDrop {
     //~ TRANS_ITEM fn generic_drop_glue::{{impl}}[2]::drop[0]
@@ -54,11 +54,11 @@ impl Drop for NonGenericWithDrop {
 
 //~ TRANS_ITEM fn generic_drop_glue::main[0]
 fn main() {
-    //~ TRANS_ITEM fn core::ptr[0]::drop_in_place[0]<generic_drop_glue::StructWithDrop[0]<i8, char>> @@ generic_drop_glue.cgu-0[Internal]
+    //~ TRANS_ITEM fn core::ptr[0]::drop_in_place[0]<generic_drop_glue::StructWithDrop[0]<i8, char>> @@ generic_drop_glue0[Internal]
     //~ TRANS_ITEM fn generic_drop_glue::{{impl}}[0]::drop[0]<i8, char>
     let _ = StructWithDrop { x: 0i8, y: 'a' }.x;
 
-    //~ TRANS_ITEM fn core::ptr[0]::drop_in_place[0]<generic_drop_glue::StructWithDrop[0]<&str, generic_drop_glue::NonGenericNoDrop[0]>> @@ generic_drop_glue.cgu-0[Internal]
+    //~ TRANS_ITEM fn core::ptr[0]::drop_in_place[0]<generic_drop_glue::StructWithDrop[0]<&str, generic_drop_glue::NonGenericNoDrop[0]>> @@ generic_drop_glue0[Internal]
     //~ TRANS_ITEM fn generic_drop_glue::{{impl}}[0]::drop[0]<&str, generic_drop_glue::NonGenericNoDrop[0]>
     let _ = StructWithDrop { x: "&str", y: NonGenericNoDrop(0) }.y;
 
@@ -67,17 +67,17 @@ fn main() {
 
     // This is supposed to generate drop-glue because it contains a field that
     // needs to be dropped.
-    //~ TRANS_ITEM fn core::ptr[0]::drop_in_place[0]<generic_drop_glue::StructNoDrop[0]<generic_drop_glue::NonGenericWithDrop[0], f64>> @@ generic_drop_glue.cgu-0[Internal]
+    //~ TRANS_ITEM fn core::ptr[0]::drop_in_place[0]<generic_drop_glue::StructNoDrop[0]<generic_drop_glue::NonGenericWithDrop[0], f64>> @@ generic_drop_glue0[Internal]
     let _ = StructNoDrop { x: NonGenericWithDrop(0), y: 0f64 }.y;
 
-    //~ TRANS_ITEM fn core::ptr[0]::drop_in_place[0]<generic_drop_glue::EnumWithDrop[0]<i32, i64>> @@ generic_drop_glue.cgu-0[Internal]
+    //~ TRANS_ITEM fn core::ptr[0]::drop_in_place[0]<generic_drop_glue::EnumWithDrop[0]<i32, i64>> @@ generic_drop_glue0[Internal]
     //~ TRANS_ITEM fn generic_drop_glue::{{impl}}[1]::drop[0]<i32, i64>
     let _ = match EnumWithDrop::A::<i32, i64>(0) {
         EnumWithDrop::A(x) => x,
         EnumWithDrop::B(x) => x as i32
     };
 
-    //~TRANS_ITEM fn core::ptr[0]::drop_in_place[0]<generic_drop_glue::EnumWithDrop[0]<f64, f32>> @@ generic_drop_glue.cgu-0[Internal]
+    //~TRANS_ITEM fn core::ptr[0]::drop_in_place[0]<generic_drop_glue::EnumWithDrop[0]<f64, f32>> @@ generic_drop_glue0[Internal]
     //~ TRANS_ITEM fn generic_drop_glue::{{impl}}[1]::drop[0]<f64, f32>
     let _ = match EnumWithDrop::B::<f64, f32>(1.0) {
         EnumWithDrop::A(x) => x,
diff --git a/src/test/codegen-units/item-collection/instantiation-through-vtable.rs b/src/test/codegen-units/item-collection/instantiation-through-vtable.rs
index 9c6bdb6624e..875cacb3907 100644
--- a/src/test/codegen-units/item-collection/instantiation-through-vtable.rs
+++ b/src/test/codegen-units/item-collection/instantiation-through-vtable.rs
@@ -31,13 +31,13 @@ impl<T> Trait for Struct<T> {
 fn main() {
     let s1 = Struct { _a: 0u32 };
 
-    //~ TRANS_ITEM fn core::ptr[0]::drop_in_place[0]<instantiation_through_vtable::Struct[0]<u32>> @@ instantiation_through_vtable.cgu-0[Internal]
+    //~ TRANS_ITEM fn core::ptr[0]::drop_in_place[0]<instantiation_through_vtable::Struct[0]<u32>> @@ instantiation_through_vtable0[Internal]
     //~ TRANS_ITEM fn instantiation_through_vtable::{{impl}}[0]::foo[0]<u32>
     //~ TRANS_ITEM fn instantiation_through_vtable::{{impl}}[0]::bar[0]<u32>
     let _ = &s1 as &Trait;
 
     let s1 = Struct { _a: 0u64 };
-    //~ TRANS_ITEM fn core::ptr[0]::drop_in_place[0]<instantiation_through_vtable::Struct[0]<u64>> @@ instantiation_through_vtable.cgu-0[Internal]
+    //~ TRANS_ITEM fn core::ptr[0]::drop_in_place[0]<instantiation_through_vtable::Struct[0]<u64>> @@ instantiation_through_vtable0[Internal]
     //~ TRANS_ITEM fn instantiation_through_vtable::{{impl}}[0]::foo[0]<u64>
     //~ TRANS_ITEM fn instantiation_through_vtable::{{impl}}[0]::bar[0]<u64>
     let _ = &s1 as &Trait;
diff --git a/src/test/codegen-units/item-collection/non-generic-drop-glue.rs b/src/test/codegen-units/item-collection/non-generic-drop-glue.rs
index 5f70ff396dd..a6081b2c5eb 100644
--- a/src/test/codegen-units/item-collection/non-generic-drop-glue.rs
+++ b/src/test/codegen-units/item-collection/non-generic-drop-glue.rs
@@ -13,7 +13,7 @@
 
 #![deny(dead_code)]
 
-//~ TRANS_ITEM fn core::ptr[0]::drop_in_place[0]<non_generic_drop_glue::StructWithDrop[0]> @@ non_generic_drop_glue.cgu-0[Internal]
+//~ TRANS_ITEM fn core::ptr[0]::drop_in_place[0]<non_generic_drop_glue::StructWithDrop[0]> @@ non_generic_drop_glue0[Internal]
 struct StructWithDrop {
     x: i32
 }
@@ -27,7 +27,7 @@ struct StructNoDrop {
     x: i32
 }
 
-//~ TRANS_ITEM fn core::ptr[0]::drop_in_place[0]<non_generic_drop_glue::EnumWithDrop[0]> @@ non_generic_drop_glue.cgu-0[Internal]
+//~ TRANS_ITEM fn core::ptr[0]::drop_in_place[0]<non_generic_drop_glue::EnumWithDrop[0]> @@ non_generic_drop_glue0[Internal]
 enum EnumWithDrop {
     A(i32)
 }
diff --git a/src/test/codegen-units/item-collection/transitive-drop-glue.rs b/src/test/codegen-units/item-collection/transitive-drop-glue.rs
index e41cb34eec6..8eef5f00f2a 100644
--- a/src/test/codegen-units/item-collection/transitive-drop-glue.rs
+++ b/src/test/codegen-units/item-collection/transitive-drop-glue.rs
@@ -13,11 +13,11 @@
 
 #![deny(dead_code)]
 
-//~ TRANS_ITEM fn core::ptr[0]::drop_in_place[0]<transitive_drop_glue::Root[0]> @@ transitive_drop_glue.cgu-0[Internal]
+//~ TRANS_ITEM fn core::ptr[0]::drop_in_place[0]<transitive_drop_glue::Root[0]> @@ transitive_drop_glue0[Internal]
 struct Root(Intermediate);
-//~ TRANS_ITEM fn core::ptr[0]::drop_in_place[0]<transitive_drop_glue::Intermediate[0]> @@ transitive_drop_glue.cgu-0[Internal]
+//~ TRANS_ITEM fn core::ptr[0]::drop_in_place[0]<transitive_drop_glue::Intermediate[0]> @@ transitive_drop_glue0[Internal]
 struct Intermediate(Leaf);
-//~ TRANS_ITEM fn core::ptr[0]::drop_in_place[0]<transitive_drop_glue::Leaf[0]> @@ transitive_drop_glue.cgu-0[Internal]
+//~ TRANS_ITEM fn core::ptr[0]::drop_in_place[0]<transitive_drop_glue::Leaf[0]> @@ transitive_drop_glue0[Internal]
 struct Leaf;
 
 impl Drop for Leaf {
@@ -38,15 +38,15 @@ fn main() {
 
     let _ = Root(Intermediate(Leaf));
 
-    //~ TRANS_ITEM fn core::ptr[0]::drop_in_place[0]<transitive_drop_glue::RootGen[0]<u32>> @@ transitive_drop_glue.cgu-0[Internal]
-    //~ TRANS_ITEM fn core::ptr[0]::drop_in_place[0]<transitive_drop_glue::IntermediateGen[0]<u32>> @@ transitive_drop_glue.cgu-0[Internal]
-    //~ TRANS_ITEM fn core::ptr[0]::drop_in_place[0]<transitive_drop_glue::LeafGen[0]<u32>> @@ transitive_drop_glue.cgu-0[Internal]
+    //~ TRANS_ITEM fn core::ptr[0]::drop_in_place[0]<transitive_drop_glue::RootGen[0]<u32>> @@ transitive_drop_glue0[Internal]
+    //~ TRANS_ITEM fn core::ptr[0]::drop_in_place[0]<transitive_drop_glue::IntermediateGen[0]<u32>> @@ transitive_drop_glue0[Internal]
+    //~ TRANS_ITEM fn core::ptr[0]::drop_in_place[0]<transitive_drop_glue::LeafGen[0]<u32>> @@ transitive_drop_glue0[Internal]
     //~ TRANS_ITEM fn transitive_drop_glue::{{impl}}[1]::drop[0]<u32>
     let _ = RootGen(IntermediateGen(LeafGen(0u32)));
 
-    //~ TRANS_ITEM fn core::ptr[0]::drop_in_place[0]<transitive_drop_glue::RootGen[0]<i16>> @@ transitive_drop_glue.cgu-0[Internal]
-    //~ TRANS_ITEM fn core::ptr[0]::drop_in_place[0]<transitive_drop_glue::IntermediateGen[0]<i16>> @@ transitive_drop_glue.cgu-0[Internal]
-    //~ TRANS_ITEM fn core::ptr[0]::drop_in_place[0]<transitive_drop_glue::LeafGen[0]<i16>> @@ transitive_drop_glue.cgu-0[Internal]
+    //~ TRANS_ITEM fn core::ptr[0]::drop_in_place[0]<transitive_drop_glue::RootGen[0]<i16>> @@ transitive_drop_glue0[Internal]
+    //~ TRANS_ITEM fn core::ptr[0]::drop_in_place[0]<transitive_drop_glue::IntermediateGen[0]<i16>> @@ transitive_drop_glue0[Internal]
+    //~ TRANS_ITEM fn core::ptr[0]::drop_in_place[0]<transitive_drop_glue::LeafGen[0]<i16>> @@ transitive_drop_glue0[Internal]
     //~ TRANS_ITEM fn transitive_drop_glue::{{impl}}[1]::drop[0]<i16>
     let _ = RootGen(IntermediateGen(LeafGen(0i16)));
 }
diff --git a/src/test/codegen-units/item-collection/tuple-drop-glue.rs b/src/test/codegen-units/item-collection/tuple-drop-glue.rs
index 39043cf87cb..7edb1c14525 100644
--- a/src/test/codegen-units/item-collection/tuple-drop-glue.rs
+++ b/src/test/codegen-units/item-collection/tuple-drop-glue.rs
@@ -13,7 +13,7 @@
 
 #![deny(dead_code)]
 
-//~ TRANS_ITEM fn core::ptr[0]::drop_in_place[0]<tuple_drop_glue::Dropped[0]> @@ tuple_drop_glue.cgu-0[Internal]
+//~ TRANS_ITEM fn core::ptr[0]::drop_in_place[0]<tuple_drop_glue::Dropped[0]> @@ tuple_drop_glue0[Internal]
 struct Dropped;
 
 impl Drop for Dropped {
@@ -23,10 +23,10 @@ impl Drop for Dropped {
 
 //~ TRANS_ITEM fn tuple_drop_glue::main[0]
 fn main() {
-    //~ TRANS_ITEM fn core::ptr[0]::drop_in_place[0]<(u32, tuple_drop_glue::Dropped[0])> @@ tuple_drop_glue.cgu-0[Internal]
+    //~ TRANS_ITEM fn core::ptr[0]::drop_in_place[0]<(u32, tuple_drop_glue::Dropped[0])> @@ tuple_drop_glue0[Internal]
     let x = (0u32, Dropped);
 
-    //~ TRANS_ITEM fn core::ptr[0]::drop_in_place[0]<(i16, (tuple_drop_glue::Dropped[0], bool))> @@ tuple_drop_glue.cgu-0[Internal]
-    //~ TRANS_ITEM fn core::ptr[0]::drop_in_place[0]<(tuple_drop_glue::Dropped[0], bool)> @@ tuple_drop_glue.cgu-0[Internal]
+    //~ TRANS_ITEM fn core::ptr[0]::drop_in_place[0]<(i16, (tuple_drop_glue::Dropped[0], bool))> @@ tuple_drop_glue0[Internal]
+    //~ TRANS_ITEM fn core::ptr[0]::drop_in_place[0]<(tuple_drop_glue::Dropped[0], bool)> @@ tuple_drop_glue0[Internal]
     let x = (0i16, (Dropped, true));
 }
diff --git a/src/test/codegen-units/item-collection/unsizing.rs b/src/test/codegen-units/item-collection/unsizing.rs
index de7613741b2..cf0c6643238 100644
--- a/src/test/codegen-units/item-collection/unsizing.rs
+++ b/src/test/codegen-units/item-collection/unsizing.rs
@@ -57,13 +57,13 @@ fn main()
 {
     // simple case
     let bool_sized = &true;
-    //~ TRANS_ITEM fn core::ptr[0]::drop_in_place[0]<bool> @@ unsizing.cgu-0[Internal]
+    //~ TRANS_ITEM fn core::ptr[0]::drop_in_place[0]<bool> @@ unsizing0[Internal]
     //~ TRANS_ITEM fn unsizing::{{impl}}[0]::foo[0]
     let _bool_unsized = bool_sized as &Trait;
 
     let char_sized = &'a';
 
-    //~ TRANS_ITEM fn core::ptr[0]::drop_in_place[0]<char> @@ unsizing.cgu-0[Internal]
+    //~ TRANS_ITEM fn core::ptr[0]::drop_in_place[0]<char> @@ unsizing0[Internal]
     //~ TRANS_ITEM fn unsizing::{{impl}}[1]::foo[0]
     let _char_unsized = char_sized as &Trait;
 
@@ -73,13 +73,13 @@ fn main()
         _b: 2,
         _c: 3.0f64
     };
-    //~ TRANS_ITEM fn core::ptr[0]::drop_in_place[0]<f64> @@ unsizing.cgu-0[Internal]
+    //~ TRANS_ITEM fn core::ptr[0]::drop_in_place[0]<f64> @@ unsizing0[Internal]
     //~ TRANS_ITEM fn unsizing::{{impl}}[2]::foo[0]
     let _struct_unsized = struct_sized as &Struct<Trait>;
 
     // custom coercion
     let wrapper_sized = Wrapper(&0u32);
-    //~ TRANS_ITEM fn core::ptr[0]::drop_in_place[0]<u32> @@ unsizing.cgu-0[Internal]
+    //~ TRANS_ITEM fn core::ptr[0]::drop_in_place[0]<u32> @@ unsizing0[Internal]
     //~ TRANS_ITEM fn unsizing::{{impl}}[3]::foo[0]
     let _wrapper_sized = wrapper_sized as Wrapper<Trait>;
 }