[TSan] Add option to ignore capturing behavior when instrumenting (#148156)

While not needed for most applications, some tools such as
[MUST](https://www.i12.rwth-aachen.de/cms/i12/forschung/forschungsschwerpunkte/lehrstuhl-fuer-hochleistungsrechnen/~nrbe/must/)
depend on the instrumentation being present.
MUST uses the ThreadSanitizer annotation interface to detect data races
in MPI programs, where the capture tracking is detrimental as it has no
bearing on MPI data races, leading to missed races.

llvm/lib/Transforms/Instrumentation/ThreadSanitizer.cpp

@@ -80,6 +80,10 @@ static cl::opt<bool> ClCompoundReadBeforeWrite(
     "tsan-compound-read-before-write", cl::init(false),
     cl::desc("Emit special compound instrumentation for reads-before-writes"),
     cl::Hidden);
+static cl::opt<bool>
+    ClOmitNonCaptured("tsan-omit-by-pointer-capturing", cl::init(true),
+                      cl::desc("Omit accesses due to pointer capturing"),
+                      cl::Hidden);
 
 STATISTIC(NumInstrumentedReads, "Number of instrumented reads");
 STATISTIC(NumInstrumentedWrites, "Number of instrumented writes");
@@ -450,7 +454,8 @@ void ThreadSanitizer::chooseInstructionsToInstrument(
 
     const AllocaInst *AI = findAllocaForValue(Addr);
     // Instead of Addr, we should check whether its base pointer is captured.
-    if (AI && !PointerMayBeCaptured(AI, /*ReturnCaptures=*/true)) {
+    if (AI && !PointerMayBeCaptured(AI, /*ReturnCaptures=*/true) &&
+        ClOmitNonCaptured) {
       // 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).

llvm/test/Instrumentation/ThreadSanitizer/capture-no-omit.ll

@@ -0,0 +1,92 @@
+; RUN: opt < %s -passes=tsan -tsan-omit-by-pointer-capturing=0 -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(ptr)
+
+@sink = global ptr null, align 4
+
+
+define void @captured2() nounwind uwtable sanitize_thread {
+entry:
+  %ptr = alloca i32, align 4
+  %tmp = alloca ptr, align 8
+  ; transitive escape
+  store ptr %ptr, ptr %tmp, align 8
+  %0 = load ptr, ptr %tmp, align 8
+  store ptr %0, ptr @sink, align 8
+  store i32 42, ptr %ptr, align 4
+  ret void
+}
+; CHECK-LABEL: define void @captured2
+; CHECK: __tsan_write
+; CHECK: __tsan_read
+; CHECK: __tsan_write
+; CHECK: __tsan_write
+; CHECK: ret void
+
+define void @captured3() nounwind uwtable sanitize_thread {
+entry:
+  %stkobj = alloca [2 x i32], align 8
+  ; escapes due to store into global
+  store ptr %stkobj, ptr @sink, align 8
+  ; derived is captured as its base object is captured
+  %derived = getelementptr inbounds i32, ptr %stkobj, i64 1
+  store i32 42, ptr %derived, align 4
+  ret void
+}
+; CHECK-LABEL: define void @captured3
+; CHECK: __tsan_write
+; CHECK: __tsan_write
+; CHECK: ret void
+
+define void @notcaptured2() nounwind uwtable sanitize_thread {
+entry:
+  %ptr = alloca i32, align 4
+  %tmp = alloca ptr, align 8
+  store i32 42, ptr %ptr, align 4
+  ; transitive escape
+  store ptr %ptr, ptr %tmp, align 8
+  %0 = load ptr, ptr %tmp, align 8
+  store ptr %0, ptr @sink, align 8
+  ret void
+}
+; CHECK-LABEL: define void @notcaptured2
+; CHECK: __tsan_write
+; CHECK: __tsan_write
+; CHECK: __tsan_read
+; CHECK: __tsan_write
+; CHECK: ret void
+
+define void @notcaptured3(i1 %cond) nounwind uwtable sanitize_thread {
+entry:
+  %stkobj = alloca [2 x i32], align 8
+  %derived = getelementptr inbounds i32, ptr %stkobj, i64 1
+  %ptr = select i1 %cond, ptr %derived, ptr %stkobj
+  store i32 42, ptr %ptr, align 4
+  ret void
+}
+; CHECK-LABEL: define void @notcaptured3
+; CHECK: __tsan_write
+; CHECK: ret void
+
+define void @notcaptured4() nounwind uwtable sanitize_thread {
+entry:
+  %stkobj = alloca [10 x i8], align 1
+  br label %loop
+
+exit:
+  ret void
+
+loop:
+  %count = phi i32 [ 0, %entry ], [ %addone, %loop ]
+  %derived = phi ptr [ %stkobj, %entry ], [ %ptraddone, %loop ]
+  store i32 %count, ptr %derived, align 4
+  %ptraddone = getelementptr inbounds i32, ptr %derived, i64 1
+  %addone = add nuw nsw i32 %count, 1
+  %eq10 = icmp eq i32 %addone, 10
+  br i1 %eq10, label %exit, label %loop
+}
+; CHECK-LABEL: define void @notcaptured4
+; CHECK: ret void
+; CHECK: __tsan_write

llvm/test/Instrumentation/ThreadSanitizer/capture.ll

@@ -45,6 +45,7 @@ entry:
 ; CHECK-LABEL: define void @captured2
 ; CHECK: __tsan_write
 ; CHECK: __tsan_write
+; CHECK-NOT: __tsan_write
 ; CHECK: ret void
 
 define void @captured3() nounwind uwtable sanitize_thread {
@@ -101,6 +102,7 @@ entry:
 ; CHECK-LABEL: define void @notcaptured2
 ; CHECK: __tsan_write
 ; CHECK: __tsan_write
+; CHECK-NOT: __tsan_write
 ; CHECK: ret void
 
 define void @notcaptured3(i1 %cond) nounwind uwtable sanitize_thread {