Auto merge of #30900 - michaelwoerister:trans_item_collect, r=nikomatsakis

The purpose of the translation item collector is to find all monomorphic instances of functions, methods and statics that need to be translated into LLVM IR in order to compile the current crate.

So far these instances have been discovered lazily during the trans path. For incremental compilation we want to know the set of these instances in advance, and that is what the trans::collect module provides.
In the future, incremental and regular translation will be driven by the collector implemented here.

r? @nikomatsakis
cc @rust-lang/compiler

Translation Item Collection
===========================

This module is responsible for discovering all items that will contribute to
to code generation of the crate. The important part here is that it not only
needs to find syntax-level items (functions, structs, etc) but also all
their monomorphized instantiations. Every non-generic, non-const function
maps to one LLVM artifact. Every generic function can produce
from zero to N artifacts, depending on the sets of type arguments it
is instantiated with.
This also applies to generic items from other crates: A generic definition
in crate X might produce monomorphizations that are compiled into crate Y.
We also have to collect these here.

The following kinds of "translation items" are handled here:

 - Functions
 - Methods
 - Closures
 - Statics
 - Drop glue

The following things also result in LLVM artifacts, but are not collected
here, since we instantiate them locally on demand when needed in a given
codegen unit:

 - Constants
 - Vtables
 - Object Shims

General Algorithm
-----------------
Let's define some terms first:

 - A "translation item" is something that results in a function or global in
   the LLVM IR of a codegen unit. Translation items do not stand on their
   own, they can reference other translation items. For example, if function
   `foo()` calls function `bar()` then the translation item for `foo()`
   references the translation item for function `bar()`. In general, the
   definition for translation item A referencing a translation item B is that
   the LLVM artifact produced for A references the LLVM artifact produced
   for B.

 - Translation items and the references between them for a directed graph,
   where the translation items are the nodes and references form the edges.
   Let's call this graph the "translation item graph".

 - The translation item graph for a program contains all translation items
   that are needed in order to produce the complete LLVM IR of the program.

The purpose of the algorithm implemented in this module is to build the
translation item graph for the current crate. It runs in two phases:

 1. Discover the roots of the graph by traversing the HIR of the crate.
 2. Starting from the roots, find neighboring nodes by inspecting the MIR
    representation of the item corresponding to a given node, until no more
    new nodes are found.

The roots of the translation item graph correspond to the non-generic
syntactic items in the source code. We find them by walking the HIR of the
crate, and whenever we hit upon a function, method, or static item, we
create a translation item consisting of the items DefId and, since we only
consider non-generic items, an empty type-substitution set.

Given a translation item node, we can discover neighbors by inspecting its
MIR. We walk the MIR and any time we hit upon something that signifies a
reference to another translation item, we have found a neighbor. Since the
translation item we are currently at is always monomorphic, we also know the
concrete type arguments of its neighbors, and so all neighbors again will be
monomorphic. The specific forms a reference to a neighboring node can take
in MIR are quite diverse. Here is an overview:

The most obvious form of one translation item referencing another is a
function or method call (represented by a CALL terminator in MIR). But
calls are not the only thing that might introduce a reference between two
function translation items, and as we will see below, they are just a
specialized of the form described next, and consequently will don't get any
special treatment in the algorithm.

A function does not need to actually be called in order to be a neighbor of
another function. It suffices to just take a reference in order to introduce
an edge. Consider the following example:

```rust
fn print_val<T: Display>(x: T) {
    println!("{}", x);
}

fn call_fn(f: &Fn(i32), x: i32) {
    f(x);
}

fn main() {
    let print_i32 = print_val::<i32>;
    call_fn(&print_i32, 0);
}
```
The MIR of none of these functions will contain an explicit call to
`print_val::<i32>`. Nonetheless, in order to translate this program, we need
an instance of this function. Thus, whenever we encounter a function or
method in operand position, we treat it as a neighbor of the current
translation item. Calls are just a special case of that.

In a way, closures are a simple case. Since every closure object needs to be
constructed somewhere, we can reliably discover them by observing
`RValue::Aggregate` expressions with `AggregateKind::Closure`. This is also
true for closures inlined from other crates.

Drop glue translation items are introduced by MIR drop-statements. The
generated translation item will again have drop-glue item neighbors if the
type to be dropped contains nested values that also need to be dropped. It
might also have a function item neighbor for the explicit `Drop::drop`
implementation of its type.

A subtle way of introducing neighbor edges is by casting to a trait object.
Since the resulting fat-pointer contains a reference to a vtable, we need to
instantiate all object-save methods of the trait, as we need to store
pointers to these functions even if they never get called anywhere. This can
be seen as a special case of taking a function reference.

Since `Box` expression have special compiler support, no explicit calls to
`exchange_malloc()` and `exchange_free()` may show up in MIR, even if the
compiler will generate them. We have to observe `Rvalue::Box` expressions
and Box-typed drop-statements for that purpose.

Interaction with Cross-Crate Inlining
-------------------------------------
The binary of a crate will not only contain machine code for the items
defined in the source code of that crate. It will also contain monomorphic
instantiations of any extern generic functions and of functions marked with
The collection algorithm handles this more or less transparently. When
constructing a neighbor node for an item, the algorithm will always call
`inline::get_local_instance()` before proceeding. If no local instance can
be acquired (e.g. for a function that is just linked to) no node is created;
which is exactly what we want, since no machine code should be generated in
the current crate for such an item. On the other hand, if we can
successfully inline the function, we subsequently can just treat it like a
local item, walking it's MIR et cetera.

Eager and Lazy Collection Mode
------------------------------
Translation item collection can be performed in one of two modes:

 - Lazy mode means that items will only be instantiated when actually
   referenced. The goal is to produce the least amount of machine code
   possible.

 - Eager mode is meant to be used in conjunction with incremental compilation
   where a stable set of translation items is more important than a minimal
   one. Thus, eager mode will instantiate drop-glue for every drop-able type
   in the crate, even of no drop call for that type exists (yet). It will
   also instantiate default implementations of trait methods, something that
   otherwise is only done on demand.

Open Issues
-----------
Some things are not yet fully implemented in the current version of this
module.

Since no MIR is constructed yet for initializer expressions of constants and
statics we cannot inspect these properly.

Ideally, no translation item should be generated for const fns unless there
is a call to them that cannot be evaluated at compile time. At the moment
this is not implemented however: a translation item will be produced
regardless of whether it is actually needed or not.

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Author: bors

configure

@@ -1409,6 +1409,7 @@ do
     make_dir $h/test/debuginfo-gdb
     make_dir $h/test/debuginfo-lldb
     make_dir $h/test/codegen
+    make_dir $h/test/codegen-units
     make_dir $h/test/rustdoc
 done
 

mk/tests.mk

@@ -310,6 +310,7 @@ check-stage$(1)-T-$(2)-H-$(3)-exec: \
 	check-stage$(1)-T-$(2)-H-$(3)-debuginfo-gdb-exec \
 	check-stage$(1)-T-$(2)-H-$(3)-debuginfo-lldb-exec \
 	check-stage$(1)-T-$(2)-H-$(3)-codegen-exec \
+	check-stage$(1)-T-$(2)-H-$(3)-codegen-units-exec \
 	check-stage$(1)-T-$(2)-H-$(3)-doc-exec \
 	check-stage$(1)-T-$(2)-H-$(3)-pretty-exec
 
@@ -473,6 +474,7 @@ DEBUGINFO_GDB_RS := $(wildcard $(S)src/test/debuginfo/*.rs)
 DEBUGINFO_LLDB_RS := $(wildcard $(S)src/test/debuginfo/*.rs)
 CODEGEN_RS := $(wildcard $(S)src/test/codegen/*.rs)
 CODEGEN_CC := $(wildcard $(S)src/test/codegen/*.cc)
+CODEGEN_UNITS_RS := $(wildcard $(S)src/test/codegen-units/*.rs)
 RUSTDOCCK_RS := $(wildcard $(S)src/test/rustdoc/*.rs)
 
 RPASS_TESTS := $(RPASS_RS)
@@ -488,6 +490,7 @@ PRETTY_TESTS := $(PRETTY_RS)
 DEBUGINFO_GDB_TESTS := $(DEBUGINFO_GDB_RS)
 DEBUGINFO_LLDB_TESTS := $(DEBUGINFO_LLDB_RS)
 CODEGEN_TESTS := $(CODEGEN_RS) $(CODEGEN_CC)
+CODEGEN_UNITS_TESTS := $(CODEGEN_UNITS_RS)
 RUSTDOCCK_TESTS := $(RUSTDOCCK_RS)
 
 CTEST_SRC_BASE_rpass = run-pass
@@ -550,6 +553,11 @@ CTEST_BUILD_BASE_codegen = codegen
 CTEST_MODE_codegen = codegen
 CTEST_RUNTOOL_codegen = $(CTEST_RUNTOOL)
 
+CTEST_SRC_BASE_codegen-units = codegen-units
+CTEST_BUILD_BASE_codegen-units = codegen-units
+CTEST_MODE_codegen-units = codegen-units
+CTEST_RUNTOOL_codegen-units = $(CTEST_RUNTOOL)
+
 CTEST_SRC_BASE_rustdocck = rustdoc
 CTEST_BUILD_BASE_rustdocck = rustdoc
 CTEST_MODE_rustdocck = rustdoc
@@ -673,6 +681,7 @@ CTEST_DEPS_debuginfo-lldb_$(1)-T-$(2)-H-$(3) = $$(DEBUGINFO_LLDB_TESTS) \
                                                $(S)src/etc/lldb_batchmode.py \
                                                $(S)src/etc/lldb_rust_formatters.py
 CTEST_DEPS_codegen_$(1)-T-$(2)-H-$(3) = $$(CODEGEN_TESTS)
+CTEST_DEPS_codegen-units_$(1)-T-$(2)-H-$(3) = $$(CODEGEN_UNITS_TESTS)
 CTEST_DEPS_rustdocck_$(1)-T-$(2)-H-$(3) = $$(RUSTDOCCK_TESTS) \
         $$(HBIN$(1)_H_$(3))/rustdoc$$(X_$(3)) \
 	$(S)src/etc/htmldocck.py
@@ -739,7 +748,7 @@ endif
 endef
 
 CTEST_NAMES = rpass rpass-valgrind rpass-full rfail-full cfail-full rfail cfail pfail \
-	bench debuginfo-gdb debuginfo-lldb codegen rustdocck
+	bench debuginfo-gdb debuginfo-lldb codegen codegen-units rustdocck
 
 $(foreach host,$(CFG_HOST), \
  $(eval $(foreach target,$(CFG_TARGET), \
@@ -917,6 +926,7 @@ TEST_GROUPS = \
 	debuginfo-gdb \
 	debuginfo-lldb \
 	codegen \
+	codegen-units \
 	doc \
 	$(foreach docname,$(DOC_NAMES),doc-$(docname)) \
 	pretty \

src/compiletest/common.rs

@@ -25,6 +25,7 @@ pub enum Mode {
     DebugInfoLldb,
     Codegen,
     Rustdoc,
+    CodegenUnits
 }
 
 impl FromStr for Mode {
@@ -41,6 +42,7 @@ impl FromStr for Mode {
           "debuginfo-gdb" => Ok(DebugInfoGdb),
           "codegen" => Ok(Codegen),
           "rustdoc" => Ok(Rustdoc),
+          "codegen-units" => Ok(CodegenUnits),
           _ => Err(()),
         }
     }
@@ -59,6 +61,7 @@ impl fmt::Display for Mode {
             DebugInfoLldb => "debuginfo-lldb",
             Codegen => "codegen",
             Rustdoc => "rustdoc",
+            CodegenUnits => "codegen-units",
         }, f)
     }
 }

src/compiletest/runtest.rs

@@ -10,14 +10,15 @@
 
 use common::Config;
 use common::{CompileFail, ParseFail, Pretty, RunFail, RunPass, RunPassValgrind};
-use common::{Codegen, DebugInfoLldb, DebugInfoGdb, Rustdoc};
+use common::{Codegen, DebugInfoLldb, DebugInfoGdb, Rustdoc, CodegenUnits};
 use errors;
 use header::TestProps;
 use header;
 use procsrv;
 use util::logv;
 
 use std::env;
+use std::collections::HashSet;
 use std::fmt;
 use std::fs::{self, File};
 use std::io::BufReader;
@@ -56,6 +57,7 @@ pub fn run(config: Config, testfile: &Path) {
         DebugInfoLldb => run_debuginfo_lldb_test(&config, &props, &testfile),
         Codegen => run_codegen_test(&config, &props, &testfile),
         Rustdoc => run_rustdoc_test(&config, &props, &testfile),
+        CodegenUnits => run_codegen_units_test(&config, &props, &testfile),
     }
 }
 
@@ -1747,3 +1749,44 @@ fn run_rustdoc_test(config: &Config, props: &TestProps, testfile: &Path) {
         fatal_proc_rec("htmldocck failed!", &res);
     }
 }
+
+fn run_codegen_units_test(config: &Config, props: &TestProps, testfile: &Path) {
+    let proc_res = compile_test(config, props, testfile);
+
+    if !proc_res.status.success() {
+        fatal_proc_rec("compilation failed!", &proc_res);
+    }
+
+    check_no_compiler_crash(&proc_res);
+
+    let prefix = "TRANS_ITEM ";
+
+    let actual: HashSet<String> = proc_res
+        .stdout
+        .lines()
+        .filter(|line| line.starts_with(prefix))
+        .map(|s| (&s[prefix.len()..]).to_string())
+        .collect();
+
+    let expected: HashSet<String> = errors::load_errors(testfile)
+        .iter()
+        .map(|e| e.msg.trim().to_string())
+        .collect();
+
+    if actual != expected {
+        let mut missing: Vec<_> = expected.difference(&actual).collect();
+        missing.sort();
+
+        let mut too_much: Vec<_> = actual.difference(&expected).collect();
+        too_much.sort();
+
+        println!("Expected and actual sets of codegen-items differ.\n\
+                  These items should have been contained but were not:\n\n\
+                  {}\n\n\
+                  These items were contained but should not have been:\n\n\
+                  {}\n\n",
+            missing.iter().fold("".to_string(), |s1, s2| s1 + "\n" + s2),
+            too_much.iter().fold("".to_string(), |s1, s2| s1 + "\n" + s2));
+        panic!();
+    }
+}

src/librustc/front/map/definitions.rs

@@ -196,33 +196,33 @@ impl DefPathData {
 
             PositionalField |
             Field(hir::StructFieldKind::UnnamedField(_)) => {
-                InternedString::new("<field>")
+                InternedString::new("{{field}}")
             }
 
             // note that this does not show up in user printouts
             CrateRoot => {
-                InternedString::new("<root>")
+                InternedString::new("{{root}}")
             }
 
             // note that this does not show up in user printouts
             InlinedRoot(_) => {
-                InternedString::new("<inlined-root>")
+                InternedString::new("{{inlined-root}}")
             }
 
             Misc => {
-                InternedString::new("?")
+                InternedString::new("{{?}}")
             }
 
             ClosureExpr => {
-                InternedString::new("<closure>")
+                InternedString::new("{{closure}}")
             }
 
             StructCtor => {
-                InternedString::new("<constructor>")
+                InternedString::new("{{constructor}}")
             }
 
             Initializer => {
-                InternedString::new("<initializer>")
+                InternedString::new("{{initializer}}")
             }
         }
     }

src/librustc/middle/cstore.rs

@@ -223,6 +223,8 @@ pub trait CrateStore<'tcx> : Any {
                           -> FoundAst<'tcx>;
     fn maybe_get_item_mir(&self, tcx: &ty::ctxt<'tcx>, def: DefId)
                           -> Option<Mir<'tcx>>;
+    fn is_item_mir_available(&self, def: DefId) -> bool;
+
     // This is basically a 1-based range of ints, which is a little
     // silly - I may fix that.
     fn crates(&self) -> Vec<ast::CrateNum>;
@@ -401,6 +403,9 @@ impl<'tcx> CrateStore<'tcx> for DummyCrateStore {
                           -> FoundAst<'tcx> { unimplemented!() }
     fn maybe_get_item_mir(&self, tcx: &ty::ctxt<'tcx>, def: DefId)
                           -> Option<Mir<'tcx>> { unimplemented!() }
+    fn is_item_mir_available(&self, def: DefId) -> bool {
+        unimplemented!()
+    }
 
     // This is basically a 1-based range of ints, which is a little
     // silly - I may fix that.

src/librustc/middle/ty/context.rs

@@ -563,7 +563,7 @@ impl<'tcx> ctxt<'tcx> {
             const_qualif_map: RefCell::new(NodeMap()),
             custom_coerce_unsized_kinds: RefCell::new(DefIdMap()),
             cast_kinds: RefCell::new(NodeMap()),
-            fragment_infos: RefCell::new(DefIdMap()),
+            fragment_infos: RefCell::new(DefIdMap())
        }, f)
     }
 }

src/librustc/middle/ty/maps.rs

@@ -13,7 +13,7 @@ use middle::def_id::DefId;
 use middle::ty;
 use std::marker::PhantomData;
 use std::rc::Rc;
-use syntax::attr;
+use syntax::{attr, ast};
 
 macro_rules! dep_map_ty {
     ($ty_name:ident : $node_name:ident ($key:ty) -> $value:ty) => {
@@ -42,3 +42,4 @@ dep_map_ty! { InherentImpls: InherentImpls(DefId) -> Rc<Vec<DefId>> }
 dep_map_ty! { ImplItems: ImplItems(DefId) -> Vec<ty::ImplOrTraitItemId> }
 dep_map_ty! { TraitItems: TraitItems(DefId) -> Rc<Vec<ty::ImplOrTraitItem<'tcx>>> }
 dep_map_ty! { ReprHints: ReprHints(DefId) -> Rc<Vec<attr::ReprAttr>> }
+dep_map_ty! { InlinedClosures: Hir(DefId) -> ast::NodeId }

src/librustc/mir/repr.rs

@@ -25,7 +25,7 @@ use std::{iter, u32};
 use std::ops::{Index, IndexMut};
 
 /// Lowered representation of a single function.
-#[derive(RustcEncodable, RustcDecodable)]
+#[derive(Clone, RustcEncodable, RustcDecodable)]
 pub struct Mir<'tcx> {
     /// List of basic blocks. References to basic block use a newtyped index type `BasicBlock`
     /// that indexes into this vector.
@@ -146,7 +146,7 @@ pub enum BorrowKind {
 
 // A "variable" is a binding declared by the user as part of the fn
 // decl, a let, etc.
-#[derive(RustcEncodable, RustcDecodable)]
+#[derive(Clone, RustcEncodable, RustcDecodable)]
 pub struct VarDecl<'tcx> {
     pub mutability: Mutability,
     pub name: Name,
@@ -155,7 +155,7 @@ pub struct VarDecl<'tcx> {
 
 // A "temp" is a temporary that we place on the stack. They are
 // anonymous, always mutable, and have only a type.
-#[derive(RustcEncodable, RustcDecodable)]
+#[derive(Clone, RustcEncodable, RustcDecodable)]
 pub struct TempDecl<'tcx> {
     pub ty: Ty<'tcx>,
 }
@@ -171,7 +171,7 @@ pub struct TempDecl<'tcx> {
 //
 // there is only one argument, of type `(i32, u32)`, but two bindings
 // (`x` and `y`).
-#[derive(RustcEncodable, RustcDecodable)]
+#[derive(Clone, RustcEncodable, RustcDecodable)]
 pub struct ArgDecl<'tcx> {
     pub ty: Ty<'tcx>,
 }
@@ -207,14 +207,14 @@ impl Debug for BasicBlock {
 ///////////////////////////////////////////////////////////////////////////
 // BasicBlock and Terminator
 
-#[derive(Debug, RustcEncodable, RustcDecodable)]
+#[derive(Clone, Debug, RustcEncodable, RustcDecodable)]
 pub struct BasicBlockData<'tcx> {
     pub statements: Vec<Statement<'tcx>>,
     pub terminator: Option<Terminator<'tcx>>,
     pub is_cleanup: bool,
 }
 
-#[derive(RustcEncodable, RustcDecodable)]
+#[derive(Clone, RustcEncodable, RustcDecodable)]
 pub enum Terminator<'tcx> {
     /// block should have one successor in the graph; we jump there
     Goto {
@@ -481,13 +481,13 @@ impl<'tcx> Terminator<'tcx> {
 ///////////////////////////////////////////////////////////////////////////
 // Statements
 
-#[derive(RustcEncodable, RustcDecodable)]
+#[derive(Clone, RustcEncodable, RustcDecodable)]
 pub struct Statement<'tcx> {
     pub span: Span,
     pub kind: StatementKind<'tcx>,
 }
 
-#[derive(Debug, RustcEncodable, RustcDecodable)]
+#[derive(Clone, Debug, RustcEncodable, RustcDecodable)]
 pub enum StatementKind<'tcx> {
     Assign(Lvalue<'tcx>, Rvalue<'tcx>),
     Drop(DropKind, Lvalue<'tcx>),
@@ -721,7 +721,7 @@ pub enum Rvalue<'tcx> {
     InlineAsm(InlineAsm),
 }
 
-#[derive(Clone, Debug, PartialEq, Eq, RustcEncodable, RustcDecodable)]
+#[derive(Clone, Copy, Debug, PartialEq, Eq, RustcEncodable, RustcDecodable)]
 pub enum CastKind {
     Misc,
 

src/librustc/session/config.rs

@@ -643,6 +643,8 @@ options! {DebuggingOptions, DebuggingSetter, basic_debugging_options,
           "keep the AST after lowering it to HIR"),
     show_span: Option<String> = (None, parse_opt_string,
           "show spans for compiler debugging (expr|pat|ty)"),
+    print_trans_items: Option<String> = (None, parse_opt_string,
+          "print the result of the translation item collection pass"),
 }
 
 pub fn default_lib_output() -> CrateType {

src/librustc_metadata/astencode.rs

@@ -177,6 +177,7 @@ pub fn decode_inlined_item<'tcx>(cdata: &cstore::crate_metadata,
           }
           _ => { }
         }
+
         Ok(ii)
       }
     }

src/librustc_metadata/csearch.rs

@@ -445,6 +445,11 @@ impl<'tcx> CrateStore<'tcx> for cstore::CStore {
         decoder::maybe_get_item_mir(&*cdata, tcx, def.index)
     }
 
+    fn is_item_mir_available(&self, def: DefId) -> bool {
+        let cdata = self.get_crate_data(def.krate);
+        decoder::is_item_mir_available(&*cdata, def.index)
+    }
+
     fn crates(&self) -> Vec<ast::CrateNum>
     {
         let mut result = vec![];

src/librustc_metadata/decoder.rs

@@ -830,6 +830,14 @@ pub fn maybe_get_item_ast<'tcx>(cdata: Cmd,
     }
 }
 
+pub fn is_item_mir_available<'tcx>(cdata: Cmd, id: DefIndex) -> bool {
+    if let Some(item_doc) = cdata.get_item(id) {
+        return reader::maybe_get_doc(item_doc, tag_mir as usize).is_some();
+    }
+
+    false
+}
+
 pub fn maybe_get_item_mir<'tcx>(cdata: Cmd,
                                 tcx: &ty::ctxt<'tcx>,
                                 id: DefIndex)
@@ -849,6 +857,8 @@ pub fn maybe_get_item_mir<'tcx>(cdata: Cmd,
             })
         }).unwrap();
 
+        assert!(decoder.position() == mir_doc.end);
+
         let mut def_id_and_span_translator = MirDefIdAndSpanTranslator {
             crate_metadata: cdata,
             codemap: tcx.sess.codemap(),