tsan: remove implicit memcpy in MutexSet::Desc::operator=()

[dvyukov]

Summary

The default compiler-generated MutexSet::Desc::operator=()
now contains memcpy() call since Desc become bigger.
This fails in debug mode since we call interceptor from within the runtime.
Define own operator=() using internal_memcpy().
This also makes copy ctor necessary, otherwise:
tsan_mutexset.h:33:11: warning: definition of implicit copy constructor for
'Desc' is deprecated because it has a user-declared copy assignment operator
And if we add copy ctor, we also need the default ctor
since it's called by MutexSet ctor.

Depends on D107911.

[melver]

compiler-rt/lib/tsan/rtl/tsan_mutexset.h

35

No need to implement, just make it emit the default:

Desc(const Desc&) = default;

I assume copy-constructor doesn't emit memcpy somehow?

[melver]

compiler-rt/lib/tsan/rtl/tsan_mutexset.h

35

Hmm, of course '= default' doesn't work if it doesn't end up using operator=.
In which case, explicit implementation is needed and disregard my comment.

[dvyukov]

restored MutexSet::MutexSet

[dvyukov]

In D107959#2941386, @dvyukov wrote:

restored MutexSet::MutexSet

W/o this compiler managed to insert memset before the call to MutexSet ctor (no ideas why would it do it, but restoring the ctor helps):

// Too large for stack.
alignas(MutexSet) static char mset_storage[sizeof(MutexSet)];
MutexSet &mset = *new (mset_storage) MutexSet();
4c0b4b:       4c 8d 35 56 b9 2e 03    lea    0x32eb956(%rip),%r14        # 37ac4a8 <_ZZN6__tsan2v312RestoreStackEjNS0_9EventTypeENS_3SidENS_5EpochEmmmPNS_17VarSizeStackTraceEPNS_8MutexSetEPmE12mset_storage>
4c0b52:       ba 10 03 00 00          mov    $0x310,%edx
4c0b57:       4c 89 f7                mov    %r14,%rdi
4c0b5a:       31 f6                   xor    %esi,%esi
4c0b5c:       e8 8f 7f f9 ff          callq  458af0 <__interceptor_memset>
4c0b61:       4c 89 f7                mov    %r14,%rdi
4c0b64:       e8 57 be fe ff          callq  4ac9c0 <_ZN6__tsan8MutexSetC2Ev>

compiler-rt/lib/tsan/rtl/tsan_mutexset.h

35

Yes, I think the compiler can happily emit memcpy into the generated copy ctor.

compiler-rt/lib/tsan/rtl/tsan_mutexset.h

 #include "tsan_defs.h"
 
 namespace __tsan {
 
 class MutexSet {
  public:
   // Holds limited number of mutexes.
   // The oldest mutexes are discarded on overflow.
-  static const uptr kMaxSize = 16;
+  static constexpr uptr kMaxSize = 16;
   struct Desc {
     uptr addr;
     StackID stack_id;
     u64 id;
     u64 epoch;
     u32 seq;
     u32 count;
     bool write;
+
+    Desc() { internal_memset(this, 0, sizeof(*this)); }
+    Desc(const Desc& other) { *this = other; }
+    Desc& operator=(const MutexSet::Desc& other) {
+      internal_memcpy(this, &other, sizeof(*this));
+      return *this;
+    }
   };
 
   MutexSet();
   // The 'id' is obtained from SyncVar::GetId().
   void Add(u64 id, bool write, u64 epoch);
   void Del(u64 id, bool write);
   void Remove(u64 id);  // Removes the mutex completely (if it's destroyed).
   void AddAddr(uptr addr, StackID stack_id, bool write);
   void DelAddr(uptr addr, bool destroy = false);
   uptr Size() const;
   Desc Get(uptr i) const;
 
-  MutexSet(const MutexSet& other) { *this = other; }
-  void operator=(const MutexSet &other) {
-    internal_memcpy(this, &other, sizeof(*this));
-  }
-
  private:
 #if !SANITIZER_GO
   u32 seq_ = 0;
   uptr size_ = 0;
   Desc descs_[kMaxSize];
 
   void RemovePos(uptr i);
 #endif

compiler-rt/lib/tsan/rtl/tsan_mutexset.cpp

 //===-- tsan_mutexset.cpp -------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 //
 // This file is a part of ThreadSanitizer (TSan), a race detector.
 //
 //===----------------------------------------------------------------------===//
 #include "tsan_mutexset.h"
 #include "tsan_rtl.h"
 
 namespace __tsan {
 
-const uptr MutexSet::kMaxSize;
-
 MutexSet::MutexSet() {
-  internal_memset(&descs_, 0, sizeof(descs_));
 }
 
 void MutexSet::Add(u64 id, bool write, u64 epoch) {
   // Look up existing mutex with the same id.
   for (uptr i = 0; i < size_; i++) {
     if (descs_[i].id == id) {
       descs_[i].count++;
       descs_[i].epoch = epoch;