Remove extra uses of ClearAllBits

ArenaBitVector creation guarantees it starts empty. Add a debug
check to make sure this assumption doesn't change.

Note that ArenaAllocator guarantees zero-initialized memory but
ScopedArenaAllocators do not. This is fine either way since the
BitVector constructor calls ClearAllBits.

Bug: 329037671
Test: art/test/testrunner/testrunner.py --host --64 --optimizing -b
Change-Id: Icbf5e5dd1869e80b5d5828ecca9f13de30c0242b

1 files changed, 6 insertions, 0 deletions

diff --git a/libartbase/base/bit_vector.cc b/libartbase/base/bit_vector.cc
index 8e3d4c9bf7..85f326385e 100644
--- a/libartbase/base/bit_vector.cc
+++ b/libartbase/base/bit_vector.cc
@@ -46,6 +46,12 @@ BitVector::BitVector(uint32_t start_bits,
               BitsToWords(start_bits),
               static_cast<uint32_t*>(allocator->Alloc(BitsToWords(start_bits) * kWordBytes))) {
   // We don't know if the allocator cleared things.
+  // TODO(solanes): We should be able to remove this call to `ClearAllBits`. Currently we have:
+  // * `MallocAllocator` and `ArenaAllocator` which sets it to zero, and
+  // * `ScopedArenaAllocator` which does not.
+  // We also have `NoopAllocator` but that allocator should never call this method (as the Alloc
+  // call will turn into a LOG(FATAL)).
+  // As a note, MallocAllocator is a misnomer as it uses `calloc` which sets the memory to zero.
   ClearAllBits();
 }