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rustc: Update LLVM, remove dead wasm code
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This commit updates the LLVM branch to the rebased version of the
upstream release/8.x branch. This includes a wasm patch which means that
the `rewrite_imports` pass in rustc is no longer needed (yay!) and we
can instead rely on `wasm-import-module`, an attribute we're already
emitting, to take care of all the work.
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@alexcrichton
alexcrichton committed Feb 26, 2019
1 parent da57320 commit c196097
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Showing 5 changed files with 2 additions and 152 deletions.
1 change: 0 additions & 1 deletion src/librustc_codegen_llvm/back/link.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -698,7 +698,6 @@ fn link_natively(sess: &Session,
}

if sess.opts.target_triple.triple() == "wasm32-unknown-unknown" {
wasm::rewrite_imports(&out_filename, &codegen_results.crate_info.wasm_imports);
wasm::add_producer_section(
&out_filename,
&sess.edition().to_string(),
Expand Down
126 changes: 0 additions & 126 deletions src/librustc_codegen_llvm/back/wasm.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2,116 +2,11 @@ use std::fs;
use std::path::Path;
use std::str;

use rustc_data_structures::fx::FxHashMap;
use serialize::leb128;

// https://webassembly.github.io/spec/core/binary/modules.html#binary-importsec
const WASM_IMPORT_SECTION_ID: u8 = 2;
const WASM_CUSTOM_SECTION_ID: u8 = 0;

const WASM_EXTERNAL_KIND_FUNCTION: u8 = 0;
const WASM_EXTERNAL_KIND_TABLE: u8 = 1;
const WASM_EXTERNAL_KIND_MEMORY: u8 = 2;
const WASM_EXTERNAL_KIND_GLOBAL: u8 = 3;

/// Rewrite the module imports are listed from in a wasm module given the field
/// name to module name mapping in `import_map`.
///
/// LLVM 6 which we're using right now doesn't have the ability to configure the
/// module a wasm symbol is import from. Rather all imported symbols come from
/// the bland `"env"` module unconditionally. Furthermore we'd *also* need
/// support in LLD for preserving these import modules, which it unfortunately
/// currently does not.
///
/// This function is intended as a hack for now where we manually rewrite the
/// wasm output by LLVM to have the correct import modules listed. The
/// `#[link(wasm_import_module = "...")]` attribute in Rust translates to the
/// module that each symbol is imported from, so here we manually go through the
/// wasm file, decode it, rewrite imports, and then rewrite the wasm module.
///
/// Support for this was added to LLVM in
/// https://github.com/llvm-mirror/llvm/commit/0f32e1365, although support still
/// needs to be added, tracked at https://bugs.llvm.org/show_bug.cgi?id=37168
pub fn rewrite_imports(path: &Path, import_map: &FxHashMap<String, String>) {
if import_map.is_empty() {
return
}

let wasm = fs::read(path).expect("failed to read wasm output");
let mut ret = WasmEncoder::new();
ret.data.extend(&wasm[..8]);

// skip the 8 byte wasm/version header
for (id, raw) in WasmSections(WasmDecoder::new(&wasm[8..])) {
ret.byte(id);
if id == WASM_IMPORT_SECTION_ID {
info!("rewriting import section");
let data = rewrite_import_section(
&mut WasmDecoder::new(raw),
import_map,
);
ret.bytes(&data);
} else {
info!("carry forward section {}, {} bytes long", id, raw.len());
ret.bytes(raw);
}
}

fs::write(path, &ret.data).expect("failed to write wasm output");

fn rewrite_import_section(
wasm: &mut WasmDecoder<'_>,
import_map: &FxHashMap<String, String>,
)
-> Vec<u8>
{
let mut dst = WasmEncoder::new();
let n = wasm.u32();
dst.u32(n);
info!("rewriting {} imports", n);
for _ in 0..n {
rewrite_import_entry(wasm, &mut dst, import_map);
}
return dst.data
}

fn rewrite_import_entry(wasm: &mut WasmDecoder<'_>,
dst: &mut WasmEncoder,
import_map: &FxHashMap<String, String>) {
// More info about the binary format here is available at:
// https://webassembly.github.io/spec/core/binary/modules.html#import-section
//
// Note that you can also find the whole point of existence of this
// function here, where we map the `module` name to a different one if
// we've got one listed.
let module = wasm.str();
let field = wasm.str();
let new_module = if module == "env" {
import_map.get(field).map(|s| &**s).unwrap_or(module)
} else {
module
};
info!("import rewrite ({} => {}) / {}", module, new_module, field);
dst.str(new_module);
dst.str(field);
let kind = wasm.byte();
dst.byte(kind);
match kind {
WASM_EXTERNAL_KIND_FUNCTION => dst.u32(wasm.u32()),
WASM_EXTERNAL_KIND_TABLE => {
dst.byte(wasm.byte()); // element_type
dst.limits(wasm.limits());
}
WASM_EXTERNAL_KIND_MEMORY => dst.limits(wasm.limits()),
WASM_EXTERNAL_KIND_GLOBAL => {
dst.byte(wasm.byte()); // content_type
dst.bool(wasm.bool()); // mutable
}
b => panic!("unknown kind: {}", b),
}
}
}

/// Adds or augment the existing `producers` section to encode information about
/// the Rust compiler used to produce the wasm file.
pub fn add_producer_section(
Expand Down Expand Up @@ -266,15 +161,6 @@ impl<'a> WasmDecoder<'a> {
let len = self.u32();
str::from_utf8(self.skip(len as usize)).unwrap()
}

fn bool(&mut self) -> bool {
self.byte() == 1
}

fn limits(&mut self) -> (u32, Option<u32>) {
let has_max = self.bool();
(self.u32(), if has_max { Some(self.u32()) } else { None })
}
}

struct WasmEncoder {
Expand Down Expand Up @@ -302,16 +188,4 @@ impl WasmEncoder {
fn str(&mut self, val: &str) {
self.bytes(val.as_bytes())
}

fn bool(&mut self, b: bool) {
self.byte(b as u8);
}

fn limits(&mut self, limits: (u32, Option<u32>)) {
self.bool(limits.1.is_some());
self.u32(limits.0);
if let Some(c) = limits.1 {
self.u32(c);
}
}
}
24 changes: 1 addition & 23 deletions src/librustc_codegen_ssa/base.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -16,7 +16,7 @@
use crate::{ModuleCodegen, ModuleKind, CachedModuleCodegen};

use rustc::dep_graph::cgu_reuse_tracker::CguReuse;
use rustc::hir::def_id::{CrateNum, DefId, LOCAL_CRATE};
use rustc::hir::def_id::{DefId, LOCAL_CRATE};
use rustc::middle::lang_items::StartFnLangItem;
use rustc::middle::weak_lang_items;
use rustc::mir::mono::{Stats, CodegenUnitNameBuilder};
Expand Down Expand Up @@ -816,21 +816,11 @@ impl CrateInfo {
used_crates_dynamic: cstore::used_crates(tcx, LinkagePreference::RequireDynamic),
used_crates_static: cstore::used_crates(tcx, LinkagePreference::RequireStatic),
used_crate_source: Default::default(),
wasm_imports: Default::default(),
lang_item_to_crate: Default::default(),
missing_lang_items: Default::default(),
};
let lang_items = tcx.lang_items();

let load_wasm_items = tcx.sess.crate_types.borrow()
.iter()
.any(|c| *c != config::CrateType::Rlib) &&
tcx.sess.opts.target_triple.triple() == "wasm32-unknown-unknown";

if load_wasm_items {
info.load_wasm_imports(tcx, LOCAL_CRATE);
}

let crates = tcx.crates();

let n_crates = crates.len();
Expand Down Expand Up @@ -858,9 +848,6 @@ impl CrateInfo {
if tcx.is_no_builtins(cnum) {
info.is_no_builtins.insert(cnum);
}
if load_wasm_items {
info.load_wasm_imports(tcx, cnum);
}
let missing = tcx.missing_lang_items(cnum);
for &item in missing.iter() {
if let Ok(id) = lang_items.require(item) {
Expand All @@ -879,15 +866,6 @@ impl CrateInfo {

return info
}

fn load_wasm_imports(&mut self, tcx: TyCtxt<'_, '_, '_>, cnum: CrateNum) {
self.wasm_imports.extend(tcx.wasm_import_module_map(cnum).iter().map(|(&id, module)| {
let instance = Instance::mono(tcx, id);
let import_name = tcx.symbol_name(instance);

(import_name.to_string(), module.clone())
}));
}
}

fn is_codegened_item(tcx: TyCtxt<'_, '_, '_>, id: DefId) -> bool {
Expand Down
1 change: 0 additions & 1 deletion src/librustc_codegen_ssa/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -138,7 +138,6 @@ pub struct CrateInfo {
pub used_crate_source: FxHashMap<CrateNum, Lrc<CrateSource>>,
pub used_crates_static: Vec<(CrateNum, LibSource)>,
pub used_crates_dynamic: Vec<(CrateNum, LibSource)>,
pub wasm_imports: FxHashMap<String, String>,
pub lang_item_to_crate: FxHashMap<LangItem, CrateNum>,
pub missing_lang_items: FxHashMap<CrateNum, Vec<LangItem>>,
}
Expand Down
2 changes: 1 addition & 1 deletion src/llvm-project
Submodule llvm-project updated 463 files

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