maxjhandsome
/
llvm-project
forked from OSchip/llvm-project
1
0
Fork 0
Code Issues Pull Requests Packages Releases Wiki Activity

[ThinLTO] Convert dead alias to declarations 

Summary:
This complements the fixes in r323633 and r324075 which drop the
definitions of dead functions and variables, respectively.

Fixes PR36208.

Reviewers: grimar, rafael

Subscribers: mehdi_amini, llvm-commits, inglorion

Differential Revision: https://reviews.llvm.org/D42856

llvm-svn: 324242
This commit is contained in:
Teresa Johnson 2018-02-05 15:44:27 +00:00
parent 02947b7112
commit 5a95c47730
4 changed files with 78 additions and 24 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
llvm/include/llvm/Transforms/IPO/FunctionImport.h
View File

@ -122,8 +122,9 @@ void computeDeadSymbols(
const DenseSet<GlobalValue::GUID> &GUIDPreservedSymbols,
function_ref<PrevailingType(GlobalValue::GUID)> isPrevailing);
/// Converts value \p GV to declaration.
void convertToDeclaration(GlobalValue &GV);
/// Converts value \p GV to declaration, or replaces with a declaration if
/// it is an alias. Returns true if converted, false if replaced.
bool convertToDeclaration(GlobalValue &GV);
/// Compute the set of summaries needed for a ThinLTO backend compilation of
/// \p ModulePath.

16
llvm/lib/LTO/LTOBackend.cpp
View File

@ -401,18 +401,14 @@ Error lto::backend(Config &C, AddStreamFn AddStream,
static void dropDeadSymbols(Module &Mod, const GVSummaryMapTy &DefinedGlobals,
const ModuleSummaryIndex &Index) {
auto MaybeDrop = [&](GlobalValue &GV) {
std::vector<GlobalValue *> ReplacedGlobals;
for (auto &GV : Mod.global_values())
if (GlobalValueSummary *GVS = DefinedGlobals.lookup(GV.getGUID()))
if (!Index.isGlobalValueLive(GVS))
convertToDeclaration(GV);
};
if (!Index.isGlobalValueLive(GVS) && !convertToDeclaration(GV))
ReplacedGlobals.push_back(&GV);
// Process functions and global now.
// FIXME: add support for aliases (needs support in convertToDeclaration).
for (auto &GV : Mod)
MaybeDrop(GV);
for (auto &GV : Mod.globals())
MaybeDrop(GV);
for (GlobalValue *GV : ReplacedGlobals)
GV->eraseFromParent();
}
Error lto::thinBackend(Config &Conf, unsigned Task, AddStreamFn AddStream,

38
llvm/lib/Transforms/IPO/FunctionImport.cpp
View File

@ -613,7 +613,7 @@ llvm::EmitImportsFiles(StringRef ModulePath, StringRef OutputFilename,
return std::error_code();
}
void llvm::convertToDeclaration(GlobalValue &GV) {
bool llvm::convertToDeclaration(GlobalValue &GV) {
DEBUG(dbgs() << "Converting to a declaration: `" << GV.getName() << "\n");
if (Function *F = dyn_cast<Function>(&GV)) {
F->deleteBody();
@ -624,14 +624,24 @@ void llvm::convertToDeclaration(GlobalValue &GV) {
V->setLinkage(GlobalValue::ExternalLinkage);
V->clearMetadata();
V->setComdat(nullptr);
} else
// For now we don't resolve or drop aliases. Once we do we'll
// need to add support here for creating either a function or
// variable declaration, and return the new GlobalValue* for
// the caller to use.
// Support of dropping aliases is required for correct dead code
// elimination performed in thin LTO backends (see 'dropDeadSymbols').
llvm_unreachable("Expected function or variable");
} else {
GlobalValue *NewGV;
if (GV.getValueType()->isFunctionTy())
NewGV =
Function::Create(cast<FunctionType>(GV.getValueType()),
GlobalValue::ExternalLinkage, "", GV.getParent());
else
NewGV =
new GlobalVariable(*GV.getParent(), GV.getValueType(),
/*isConstant*/ false, GlobalValue::ExternalLinkage,
/*init*/ nullptr, "",
/*insertbefore*/ nullptr, GV.getThreadLocalMode(),
GV.getType()->getAddressSpace());
NewGV->takeName(&GV);
GV.replaceAllUsesWith(NewGV);
return false;
}
return true;
}
/// Fixup WeakForLinker linkages in \p TheModule based on summary analysis.
@ -666,9 +676,13 @@ void llvm::thinLTOResolveWeakForLinkerModule(
// interposable property and possibly get inlined. Simply drop
// the definition in that case.
if (GlobalValue::isAvailableExternallyLinkage(NewLinkage) &&
GlobalValue::isInterposableLinkage(GV.getLinkage()))
convertToDeclaration(GV);
else {
GlobalValue::isInterposableLinkage(GV.getLinkage())) {
if (!convertToDeclaration(GV))
// FIXME: Change this to collect replaced GVs and later erase
// them from the parent module once thinLTOResolveWeakForLinkerGUID is
// changed to enable this for aliases.
llvm_unreachable("Expected GV to be converted");
} else {
DEBUG(dbgs() << "ODR fixing up linkage for `" << GV.getName() << "` from "
<< GV.getLinkage() << " to " << NewLinkage << "\n");
GV.setLinkage(NewLinkage);

43
llvm/test/LTO/Resolution/X86/not-prevailing-alias.ll Normal file
View File

@ -0,0 +1,43 @@
; Test to ensure that dead alias are dropped by converting to a declaration
; RUN: opt -module-summary %s -o %t1.bc
; RUN: llvm-lto2 run %t1.bc -r %t1.bc,barAlias,x \
; RUN: -r %t1.bc,bar,x -r %t1.bc,zed,px \
; RUN: -r %t1.bc,var,x -r %t1.bc,varAlias,x \
; RUN: -o %t2.o -save-temps
; Check that bar and barAlias were dropped to declarations
; RUN: llvm-dis %t2.o.1.1.promote.bc -o - | FileCheck %s --check-prefix=DROP
; DROP-DAG: declare void @bar()
; DROP-DAG: declare void @barAlias()
; DROP-DAG: @var = external global i32
; DROP-DAG: @varAlias = external global i32
; Check that 'barAlias' and 'varAlias' were not inlined.
; RUN: llvm-objdump -d %t2.o.1 | FileCheck %s
; CHECK: zed:
; CHECK-NEXT: {{.*}} pushq
; CHECK-NEXT: {{.*}} callq 0
; CHECK-NEXT: movq (%rip), %rax
; Check that 'barAlias' and 'varAlias' produced as undefined.
; RUN: llvm-readelf --symbols %t2.o.1 | FileCheck %s --check-prefix=SYMBOLS
; SYMBOLS: NOTYPE GLOBAL DEFAULT UND barAlias
; SYMBOLS: NOTYPE GLOBAL DEFAULT UND varAlias
; SYMBOLS: FUNC GLOBAL DEFAULT 2 zed
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"
@barAlias = alias void(), void()* @bar
define void @bar() {
ret void
}
@var = global i32 99
@varAlias = alias i32, i32* @var
define i32 @zed() {
call void @barAlias()
%1 = load i32, i32* @varAlias, align 4
ret i32 %1
}