Auto merge of #32557 - dotdash:issue-32518, r=nikomatsakis
Use weak_odr linkage when reusing definitions across codegen units When reuing a definition across codegen units, we obviously cannot use internal linkage, but using external linkage means that we can end up with multiple conflicting definitions of a single symbol across multiple crates. Since the definitions should all be equal semantically, we can use weak_odr linkage to resolve the situation. Fixes #32518 r? @nikomatsakis
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8f5c3f1fcf
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@ -2125,6 +2125,9 @@ extern {
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pub fn LLVMRustFreeOperandBundleDef(Bundle: OperandBundleDefRef);
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pub fn LLVMRustPositionBuilderAtStart(B: BuilderRef, BB: BasicBlockRef);
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pub fn LLVMRustSetComdat(M: ModuleRef, V: ValueRef, Name: *const c_char);
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pub fn LLVMRustUnsetComdat(V: ValueRef);
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}
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// LLVM requires symbols from this library, but apparently they're not printed
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@ -2149,6 +2152,24 @@ pub fn SetLinkage(global: ValueRef, link: Linkage) {
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}
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}
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// Externally visible symbols that might appear in multiple translation units need to appear in
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// their own comdat section so that the duplicates can be discarded at link time. This can for
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// example happen for generics when using multiple codegen units. This function simply uses the
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// value's name as the comdat value to make sure that it is in a 1-to-1 relationship to the
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// function.
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// For more details on COMDAT sections see e.g. http://www.airs.com/blog/archives/52
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pub fn SetUniqueComdat(llmod: ModuleRef, val: ValueRef) {
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unsafe {
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LLVMRustSetComdat(llmod, val, LLVMGetValueName(val));
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}
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}
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pub fn UnsetComdat(val: ValueRef) {
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unsafe {
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LLVMRustUnsetComdat(val);
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}
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}
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pub fn SetDLLStorageClass(global: ValueRef, class: DLLStorageClassTypes) {
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unsafe {
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LLVMRustSetDLLStorageClass(global, class);
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@ -2215,18 +2215,27 @@ pub fn update_linkage(ccx: &CrateContext,
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}
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}
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match id {
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Some(id) if ccx.reachable().contains(&id) => {
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let (is_reachable, is_generic) = if let Some(id) = id {
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(ccx.reachable().contains(&id), false)
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} else {
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(false, true)
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};
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// We need external linkage for items reachable from other translation units, this include
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// other codegen units in case of parallel compilations.
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if is_reachable || ccx.sess().opts.cg.codegen_units > 1 {
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if is_generic {
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// This only happens with multiple codegen units, in which case we need to use weak_odr
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// linkage because other crates might expose the same symbol. We cannot use
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// linkonce_odr here because the symbol might then get dropped before the other codegen
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// units get to link it.
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llvm::SetUniqueComdat(ccx.llmod(), llval);
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llvm::SetLinkage(llval, llvm::WeakODRLinkage);
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} else {
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llvm::SetLinkage(llval, llvm::ExternalLinkage);
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},
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_ => {
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// `id` does not refer to an item in `ccx.reachable`.
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if ccx.sess().opts.cg.codegen_units > 1 {
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llvm::SetLinkage(llval, llvm::ExternalLinkage);
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} else {
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llvm::SetLinkage(llval, llvm::InternalLinkage);
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}
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},
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}
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} else {
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llvm::SetLinkage(llval, llvm::InternalLinkage);
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}
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}
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@ -2547,8 +2556,10 @@ fn internalize_symbols(cx: &SharedCrateContext, reachable: &HashSet<&str>) {
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// then give it internal linkage.
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for ccx in cx.iter() {
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for val in iter_globals(ccx.llmod()).chain(iter_functions(ccx.llmod())) {
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let linkage = llvm::LLVMGetLinkage(val);
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// We only care about external definitions.
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if !(llvm::LLVMGetLinkage(val) == llvm::ExternalLinkage as c_uint &&
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if !((linkage == llvm::ExternalLinkage as c_uint ||
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linkage == llvm::WeakODRLinkage as c_uint) &&
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llvm::LLVMIsDeclaration(val) == 0) {
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continue;
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}
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@ -2560,6 +2571,7 @@ fn internalize_symbols(cx: &SharedCrateContext, reachable: &HashSet<&str>) {
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!reachable.contains(str::from_utf8(&name).unwrap()) {
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llvm::SetLinkage(val, llvm::InternalLinkage);
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llvm::SetDLLStorageClass(val, llvm::DefaultStorageClass);
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llvm::UnsetComdat(val);
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}
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}
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}
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@ -123,7 +123,6 @@ pub fn monomorphic_fn<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>,
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ref attrs, node: hir::ImplItemKind::Method(
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hir::MethodSig { ref decl, .. }, ref body), ..
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}) => {
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base::update_linkage(ccx, lldecl, None, base::OriginalTranslation);
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attributes::from_fn_attrs(ccx, attrs, lldecl);
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let is_first = !ccx.available_monomorphizations().borrow()
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@ -133,12 +132,14 @@ pub fn monomorphic_fn<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>,
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}
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let trans_everywhere = attr::requests_inline(attrs);
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if trans_everywhere && !is_first {
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llvm::SetLinkage(lldecl, llvm::AvailableExternallyLinkage);
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}
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if trans_everywhere || is_first {
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let origin = if is_first { base::OriginalTranslation } else { base::InlinedCopy };
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base::update_linkage(ccx, lldecl, None, origin);
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trans_fn(ccx, decl, body, lldecl, psubsts, fn_node_id);
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} else {
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// We marked the value as using internal linkage earlier, but that is illegal for
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// declarations, so switch back to external linkage.
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llvm::SetLinkage(lldecl, llvm::ExternalLinkage);
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}
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}
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@ -1189,3 +1189,16 @@ extern "C" void LLVMRustPositionBuilderAtStart(LLVMBuilderRef B, LLVMBasicBlockR
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auto point = unwrap(BB)->getFirstInsertionPt();
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unwrap(B)->SetInsertPoint(unwrap(BB), point);
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}
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extern "C" void LLVMRustSetComdat(LLVMModuleRef M, LLVMValueRef V, const char *Name) {
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Triple TargetTriple(unwrap(M)->getTargetTriple());
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GlobalObject *GV = unwrap<GlobalObject>(V);
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if (!TargetTriple.isOSBinFormatMachO()) {
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GV->setComdat(unwrap(M)->getOrInsertComdat(Name));
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}
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}
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extern "C" void LLVMRustUnsetComdat(LLVMValueRef V) {
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GlobalObject *GV = unwrap<GlobalObject>(V);
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GV->setComdat(nullptr);
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}
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@ -0,0 +1,16 @@
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// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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// no-prefer-dynamic
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// compile-flags: --crate-type=lib
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pub fn id<T>(t: T) -> T {
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t
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}
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@ -0,0 +1,25 @@
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// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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// no-prefer-dynamic
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// compile-flags: -Ccodegen-units=2 --crate-type=lib
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extern crate cgu_test;
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pub mod a {
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pub fn a() {
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::cgu_test::id(0);
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}
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}
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pub mod b {
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pub fn a() {
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::cgu_test::id(0);
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}
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}
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@ -0,0 +1,25 @@
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// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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// no-prefer-dynamic
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// compile-flags: -Ccodegen-units=2 --crate-type=lib
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extern crate cgu_test;
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pub mod a {
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pub fn a() {
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::cgu_test::id(0);
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}
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}
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pub mod b {
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pub fn a() {
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::cgu_test::id(0);
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}
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}
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@ -0,0 +1,22 @@
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// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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// no-prefer-dynamic
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// aux-build:cgu_test.rs
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// aux-build:cgu_test_a.rs
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// aux-build:cgu_test_b.rs
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extern crate cgu_test_a;
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extern crate cgu_test_b;
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fn main() {
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cgu_test_a::a::a();
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cgu_test_b::a::a();
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}
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