Changeset 294750 in webkit

Timestamp:

May 24, 2022, 9:15:40 AM (4 years ago)

Author:

Chris Dumez

Message:

Avoid unnecessary calls to fastZeroedMalloc() in FastBitVector
​https://bugs.webkit.org/show_bug.cgi?id=240812

Reviewed by Yusuke Suzuki.

We were calling fastZeroedMalloc() which would allocate the memory and memset it to 0,
only to then overwrite all (or most) of that memory with memcpy().

• Source/WTF/wtf/FastBitVector.cpp:

(WTF::FastBitVectorWordOwner::setEqualsSlow):
(WTF::FastBitVectorWordOwner::resizeSlow):

Canonical link: ​https://commits.webkit.org/250918@main

File:

• trunk/Source/WTF/wtf/FastBitVector.cpp (modified) (2 diffs)

trunk/Source/WTF/wtf/FastBitVector.cpp

@@ -35 +35 @@
 void FastBitVectorWordOwner::setEqualsSlow(const FastBitVectorWordOwner& other)
 {
-    uint32_t* newArray = static_cast<uint32_t*>(
-        FastBitVectorMalloc::zeroedMalloc(other.arrayLength() * sizeof(uint32_t)));
+    uint32_t* newArray = static_cast<uint32_t*>(FastBitVectorMalloc::malloc(other.arrayLength() * sizeof(uint32_t)));
     memcpy(newArray, other.m_words, other.arrayLength() * sizeof(uint32_t));
     if (m_words)
@@ -47 +46 @@
 {
     size_t newLength = fastBitVectorArrayLength(numBits);
-
-    RELEASE_ASSERT(newLength >= arrayLength());
+    size_t oldLength = arrayLength();
+    RELEASE_ASSERT(newLength >= oldLength);
     
-    // Use fastCalloc instead of fastRealloc because we expect the common
+    // Use fastMalloc instead of fastRealloc because we expect the common
     // use case for this method to be initializing the size of the bitvector.
     
-    uint32_t* newArray = static_cast<uint32_t*>(FastBitVectorMalloc::zeroedMalloc(newLength * sizeof(uint32_t)));
-    memcpy(newArray, m_words, arrayLength() * sizeof(uint32_t));
+    uint32_t* newArray = static_cast<uint32_t*>(FastBitVectorMalloc::malloc(newLength * sizeof(uint32_t)));
+    memcpy(newArray, m_words, oldLength * sizeof(uint32_t));
+    memset(newArray + oldLength, 0, (newLength - oldLength) * sizeof(uint32_t));
     if (m_words)
         FastBitVectorMalloc::free(m_words);