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tsan: do not instrument not captured values

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I've built some tests in WebRTC with and without this change. With this change number of __tsan_read/write calls is reduced by 20-40%, binary size decreases by 5-10% and execution time drops by ~5%. For example:

$ ls -l old/modules_unittests new/modules_unittests
-rwxr-x--- 1 dvyukov 41708976 Jan 20 18:35 old/modules_unittests
-rwxr-x--- 1 dvyukov 38294008 Jan 20 18:29 new/modules_unittests
$ objdump -d old/modules_unittests | egrep "callq.*__tsan_(read|write|unaligned)" | wc -l
239871
$ objdump -d new/modules_unittests | egrep "callq.*__tsan_(read|write|unaligned)" | wc -l
148365

http://reviews.llvm.org/D7069



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@228917 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dmitry Vyukov 2015-02-12 09:55:28 +00:00
parent f41b8e3e49
commit 95fa2f9326
2 changed files with 106 additions and 0 deletions
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15
lib/Transforms/Instrumentation/ThreadSanitizer.cpp
View File

@ -19,6 +19,8 @@
// The rest is handled by the run-time library.
//===----------------------------------------------------------------------===//
#include "llvm/Analysis/CaptureTracking.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/Transforms/Instrumentation.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/SmallString.h"
@ -68,6 +70,7 @@ STATISTIC(NumInstrumentedVtableReads, "Number of vtable ptr reads");
STATISTIC(NumOmittedReadsFromConstantGlobals,
"Number of reads from constant globals");
STATISTIC(NumOmittedReadsFromVtable, "Number of vtable reads");
STATISTIC(NumOmittedNonCaptured, "Number of accesses ignored due to capturing");
namespace {
@ -272,6 +275,7 @@ bool ThreadSanitizer::addrPointsToConstantData(Value *Addr) {
// Instrumenting some of the accesses may be proven redundant.
// Currently handled:
// - read-before-write (within same BB, no calls between)
// - not captured variables
//
// We do not handle some of the patterns that should not survive
// after the classic compiler optimizations.
@ -303,6 +307,17 @@ void ThreadSanitizer::chooseInstructionsToInstrument(
continue;
}
}
Value *Addr = isa<StoreInst>(*I)
? cast<StoreInst>(I)->getPointerOperand()
: cast<LoadInst>(I)->getPointerOperand();
if (isa<AllocaInst>(GetUnderlyingObject(Addr, nullptr)) &&
!PointerMayBeCaptured(Addr, true, true)) {
// The variable is addressable but not captured, so it cannot be
// referenced from a different thread and participate in a data race
// (see llvm/Analysis/CaptureTracking.h for details).
NumOmittedNonCaptured++;
continue;
}
All.push_back(I);
}
Local.clear();

91
test/Instrumentation/ThreadSanitizer/capture.ll Normal file
View File

@ -0,0 +1,91 @@
; RUN: opt < %s -tsan -S | FileCheck %s
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"
declare void @escape(i32*)
@sink = global i32* null, align 4
define void @captured0() nounwind uwtable sanitize_thread {
entry:
%ptr = alloca i32, align 4
; escapes due to call
call void @escape(i32* %ptr)
store i32 42, i32* %ptr, align 4
ret void
}
; CHECK-LABEL: define void @captured0
; CHECK: __tsan_write
; CHECK: ret void
define void @captured1() nounwind uwtable sanitize_thread {
entry:
%ptr = alloca i32, align 4
; escapes due to store into global
store i32* %ptr, i32** @sink, align 8
store i32 42, i32* %ptr, align 4
ret void
}
; CHECK-LABEL: define void @captured1
; CHECK: __tsan_write
; CHECK: __tsan_write
; CHECK: ret void
define void @captured2() nounwind uwtable sanitize_thread {
entry:
%ptr = alloca i32, align 4
%tmp = alloca i32*, align 8
; transitive escape
store i32* %ptr, i32** %tmp, align 8
%0 = load i32** %tmp, align 8
store i32* %0, i32** @sink, align 8
store i32 42, i32* %ptr, align 4
ret void
}
; CHECK-LABEL: define void @captured2
; CHECK: __tsan_write
; CHECK: __tsan_write
; CHECK: ret void
define void @notcaptured0() nounwind uwtable sanitize_thread {
entry:
%ptr = alloca i32, align 4
store i32 42, i32* %ptr, align 4
; escapes due to call
call void @escape(i32* %ptr)
ret void
}
; CHECK-LABEL: define void @notcaptured0
; CHECK: __tsan_write
; CHECK: ret void
define void @notcaptured1() nounwind uwtable sanitize_thread {
entry:
%ptr = alloca i32, align 4
store i32 42, i32* %ptr, align 4
; escapes due to store into global
store i32* %ptr, i32** @sink, align 8
ret void
}
; CHECK-LABEL: define void @notcaptured1
; CHECK: __tsan_write
; CHECK: __tsan_write
; CHECK: ret void
define void @notcaptured2() nounwind uwtable sanitize_thread {
entry:
%ptr = alloca i32, align 4
%tmp = alloca i32*, align 8
store i32 42, i32* %ptr, align 4
; transitive escape
store i32* %ptr, i32** %tmp, align 8
%0 = load i32** %tmp, align 8
store i32* %0, i32** @sink, align 8
ret void
}
; CHECK-LABEL: define void @notcaptured2
; CHECK: __tsan_write
; CHECK: __tsan_write
; CHECK: ret void