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[tsan] two more compile-time optimizations:

Browse Source 
- don't isntrument reads from constant globals.
Saves ~1.5% of instrumented instructions on CPU2006
(counting static instructions, not their execution).
- don't insrument reads from vtable (which is a global constant too).
Saves ~5%.

I did not measure the run-time impact of this,
but it is certainly non-negative.




git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@154444 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Kostya Serebryany 2012-04-10 22:29:17 +00:00
parent 3aef2ff514
commit cff60c1409
2 changed files with 103 additions and 11 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

53
lib/Transforms/Instrumentation/ThreadSanitizer.cpp
View File

@ -58,6 +58,8 @@ struct ThreadSanitizerStats {
size_t NumOmittedReadsBeforeWrite;
size_t NumAccessesWithBadSize;
size_t NumInstrumentedVtableWrites;
size_t NumOmittedReadsFromConstantGlobals;
size_t NumOmittedReadsFromVtable;
};
/// ThreadSanitizer: instrument the code in module to find races.
@ -72,6 +74,7 @@ struct ThreadSanitizer : public FunctionPass {
private:
void choseInstructionsToInstrument(SmallVectorImpl<Instruction*> &Local,
SmallVectorImpl<Instruction*> &All);
bool addrPointsToConstantData(Value *Addr);
TargetData *TD;
OwningPtr<FunctionBlackList> BL;
@ -145,11 +148,44 @@ bool ThreadSanitizer::doFinalization(Module &M) {
<< "; vt " << stats.NumInstrumentedVtableWrites
<< "; bs " << stats.NumAccessesWithBadSize
<< "; rbw " << stats.NumOmittedReadsBeforeWrite
<< "; rcg " << stats.NumOmittedReadsFromConstantGlobals
<< "; rvt " << stats.NumOmittedReadsFromVtable
<< "\n";
}
return true;
}
static bool isVtableAccess(Instruction *I) {
if (MDNode *Tag = I->getMetadata(LLVMContext::MD_tbaa)) {
if (Tag->getNumOperands() < 1) return false;
if (MDString *Tag1 = dyn_cast<MDString>(Tag->getOperand(0))) {
if (Tag1->getString() == "vtable pointer") return true;
}
}
return false;
}
bool ThreadSanitizer::addrPointsToConstantData(Value *Addr) {
// If this is a GEP, just analyze its pointer operand.
if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Addr))
Addr = GEP->getPointerOperand();
if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Addr)) {
if (GV->isConstant()) {
// Reads from constant globals can not race with any writes.
stats.NumOmittedReadsFromConstantGlobals++;
return true;
}
} else if(LoadInst *L = dyn_cast<LoadInst>(Addr)) {
if (isVtableAccess(L)) {
// Reads from a vtable pointer can not race with any writes.
stats.NumOmittedReadsFromVtable++;
return true;
}
}
return false;
}
// Instrumenting some of the accesses may be proven redundant.
// Currently handled:
// - read-before-write (within same BB, no calls between)
@ -173,11 +209,16 @@ void ThreadSanitizer::choseInstructionsToInstrument(
WriteTargets.insert(Store->getPointerOperand());
} else {
LoadInst *Load = cast<LoadInst>(I);
if (WriteTargets.count(Load->getPointerOperand())) {
Value *Addr = Load->getPointerOperand();
if (WriteTargets.count(Addr)) {
// We will write to this temp, so no reason to analyze the read.
stats.NumOmittedReadsBeforeWrite++;
continue;
}
if (addrPointsToConstantData(Addr)) {
// Addr points to some constant data -- it can not race with any writes.
continue;
}
}
All.push_back(I);
}
@ -236,16 +277,6 @@ bool ThreadSanitizer::runOnFunction(Function &F) {
return Res;
}
static bool isVtableAccess(Instruction *I) {
if (MDNode *Tag = I->getMetadata(LLVMContext::MD_tbaa)) {
if (Tag->getNumOperands() < 1) return false;
if (MDString *Tag1 = dyn_cast<MDString>(Tag->getOperand(0))) {
if (Tag1->getString() == "vtable pointer") return true;
}
}
return false;
}
bool ThreadSanitizer::instrumentLoadOrStore(Instruction *I) {
IRBuilder<> IRB(I);
bool IsWrite = isa<StoreInst>(*I);

61
test/Instrumentation/ThreadSanitizer/read_from_global.ll Normal file
View File

@ -0,0 +1,61 @@
; RUN: opt < %s -tsan -S | FileCheck %s
; Check that tsan does not instrument reads from constant globals.
target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
@const_global = external constant i32
define i32 @read_from_const_global() nounwind uwtable readnone {
entry:
%0 = load i32* @const_global, align 4
ret i32 %0
}
; CHECK: define i32 @read_from_const_global
; CHECK-NOT: __tsan
; CHECK: ret i32
@non_const_global = global i32 0, align 4
define i32 @read_from_non_const_global() nounwind uwtable readonly {
entry:
%0 = load i32* @non_const_global, align 4
ret i32 %0
}
; CHECK: define i32 @read_from_non_const_global
; CHECK: __tsan_read
; CHECK: ret i32
@const_global_array = external constant [10 x i32]
define i32 @read_from_const_global_array(i32 %idx) nounwind uwtable readnone {
entry:
%idxprom = sext i32 %idx to i64
%arrayidx = getelementptr inbounds [10 x i32]* @const_global_array, i64 0, i64 %idxprom
%0 = load i32* %arrayidx, align 4
ret i32 %0
}
; CHECK: define i32 @read_from_const_global_array
; CHECK-NOT: __tsan
; CHECK: ret i32
%struct.Foo = type { i32 (...)** }
define void @call_virtual_func(%struct.Foo* %f) uwtable {
entry:
%0 = bitcast %struct.Foo* %f to void (%struct.Foo*)***
%vtable = load void (%struct.Foo*)*** %0, align 8, !tbaa !3
%1 = load void (%struct.Foo*)** %vtable, align 8
call void %1(%struct.Foo* %f)
ret void
}
; CHECK: define void @call_virtual_func
; CHECK: __tsan_read
; CHECK: = load
; CHECK-NOT: __tsan_read
; CHECK: = load
; CHECK: ret void
!0 = metadata !{metadata !"int", metadata !1}
!1 = metadata !{metadata !"omnipotent char", metadata !2}
!2 = metadata !{metadata !"Simple C/C++ TBAA", null}
!3 = metadata !{metadata !"vtable pointer", metadata !2}