[sparkplug] Reserve size for bytecode offset table

Based on some test compiles (of three.js and jquery) we can get a decent
estimate of expected bytecode offset table size for a given bytecode
size. Reserve this expected size to avoid resize overhead.

Bug: v8:11420
Change-Id: I8288b01fa796e765a20b11219687fa3d23272416
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2843354
Reviewed-by: Patrick Thier <pthier@chromium.org>
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/master@{#74093}

src/baseline/baseline-compiler.cc

@@ -4,6 +4,7 @@
 
 // TODO(v8:11421): Remove #if once baseline compiler is ported to other
 // architectures.
+#include "src/base/bits.h"
 #if V8_TARGET_ARCH_IA32 || V8_TARGET_ARCH_X64 || V8_TARGET_ARCH_ARM64 || \
     V8_TARGET_ARCH_ARM || V8_TARGET_ARCH_RISCV64
 
@@ -258,6 +259,13 @@ BaselineCompiler::BaselineCompiler(
       zone_(isolate->allocator(), ZONE_NAME),
       labels_(zone_.NewArray<BaselineLabels*>(bytecode_->length())) {
   MemsetPointer(labels_, nullptr, bytecode_->length());
+
+  // Empirically determined expected size of the offset table at the 95th %ile,
+  // based on the size of the bytecode, to be:
+  //
+  //   16 + (bytecode size) / 4
+  bytecode_offset_table_builder_.Reserve(
+      base::bits::RoundUpToPowerOfTwo(16 + bytecode_->Size() / 4));
 }
 
 #define __ basm_.

src/baseline/baseline-compiler.h

@@ -42,6 +42,8 @@ class BytecodeOffsetTableBuilder {
   template <typename LocalIsolate>
   Handle<ByteArray> ToBytecodeOffsetTable(LocalIsolate* isolate);
 
+  void Reserve(size_t size) { bytes_.reserve(size); }
+
  private:
   size_t previous_pc_ = 0;
   std::vector<byte> bytes_;