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[PGO] Remove redundant counter copies for avail_extern functions. 

Differential Revision: http://reviews.llvm.org/D17654

llvm-svn: 262157
This commit is contained in:
Xinliang David Li 2016-02-27 23:11:30 +00:00
parent 6993abff14
commit 985ff20a9c
2 changed files with 42 additions and 3 deletions
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35
llvm/lib/Transforms/Instrumentation/InstrProfiling.cpp
View File

@ -286,8 +286,38 @@ static inline bool shouldRecordFunctionAddr(Function *F) {
return F->hasAddressTaken();
}
static inline Comdat *getOrCreateProfileComdat(Module &M,
static inline bool needsComdatForCounter(Function &F, Module &M) {
if (F.hasComdat())
return true;
Triple TT(M.getTargetTriple());
if (!TT.isOSBinFormatELF())
return false;
// See createPGOFuncNameVar for more details. To avoid link errors, profile
// counters for function with available_externally linkage needs to be changed
// to linkonce linkage. On ELF based systems, this leads to weak symbols to be
// created. Without using comdat, duplicate entries won't be removed by the
// linker leading to increased data segement size and raw profile size. Even
// worse, since the referenced counter from profile per-function data object
// will be resolved to the common strong definition, the profile counts for
// available_externally functions will end up being duplicated in raw profile
// data. This can result in distorted profile as the counts of those dups
// will be accumulated by the profile merger.
GlobalValue::LinkageTypes Linkage = F.getLinkage();
if (Linkage != GlobalValue::ExternalWeakLinkage &&
Linkage != GlobalValue::AvailableExternallyLinkage)
return false;
return true;
}
static inline Comdat *getOrCreateProfileComdat(Module &M, Function &F,
InstrProfIncrementInst *Inc) {
if (!needsComdatForCounter(F, M))
return nullptr;
// COFF format requires a COMDAT section to have a key symbol with the same
// name. The linker targeting COFF also requires that the COMDAT
// a section is associated to must precede the associating section. For this
@ -315,8 +345,7 @@ InstrProfiling::getOrCreateRegionCounters(InstrProfIncrementInst *Inc) {
// linking.
Function *Fn = Inc->getParent()->getParent();
Comdat *ProfileVarsComdat = nullptr;
if (Fn->hasComdat())
ProfileVarsComdat = getOrCreateProfileComdat(*M, Inc);
ProfileVarsComdat = getOrCreateProfileComdat(*M, *Fn, Inc);
uint64_t NumCounters = Inc->getNumCounters()->getZExtValue();
LLVMContext &Ctx = M->getContext();

10
llvm/test/Instrumentation/InstrProfiling/linkage.ll
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@ -7,6 +7,7 @@
@__profn_foo_weak = weak hidden constant [8 x i8] c"foo_weak"
@"__profn_linkage.ll:foo_internal" = internal constant [23 x i8] c"linkage.ll:foo_internal"
@__profn_foo_inline = linkonce_odr hidden constant [10 x i8] c"foo_inline"
@__profn_foo_extern = linkonce_odr hidden constant [10 x i8] c"foo_extern"
; COMMON: @__profc_foo = hidden global
; COMMON: @__profd_foo = hidden global
@ -36,6 +37,15 @@ define linkonce_odr void @foo_inline() {
ret void
}
; LINUX: @__profc_foo_extern = linkonce_odr hidden global {{.*}}section "__llvm_prf_cnts", comdat($__profv_foo_extern), align 8
; LINUX: @__profd_foo_extern = linkonce_odr hidden global {{.*}}section "__llvm_prf_data", comdat($__profv_foo_extern), align 8
; OTHER: @__profc_foo_extern = linkonce_odr hidden global
; OTHER: @__profd_foo_extern = linkonce_odr hidden global
define available_externally void @foo_extern() {
call void @llvm.instrprof.increment(i8* getelementptr inbounds ([10 x i8], [10 x i8]* @__profn_foo_extern, i32 0, i32 0), i64 0, i32 1, i32 0)
ret void
}
declare void @llvm.instrprof.increment(i8*, i64, i32, i32)
; OTHER: @__llvm_profile_runtime = external global i32