[BUILD] Add v8_use_zlib flag

This allows V8 to be compiled without zlib.

Currently we use zlib for 3 features:
1. Snapshot compression. The cl asserts v8_snapshot_compression
   implies v8_use_zlib.
2. Compression of translation arrays (experimental flag). The runtime
   flag is only enabled if v8_use_zlib.
3. Snapshot checksums. We fallback to a simple Fletcher algorithm if
   v8_use_zlib is false.

Change-Id: If043c3c21bba4d734573d7e1199d3ddf17b84f41
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3833817
Commit-Queue: Victor Gomes <victorgomes@chromium.org>
Reviewed-by: Jakob Linke <jgruber@chromium.org>
Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82527}

BUILD.gn

@@ -377,6 +377,10 @@ declare_args() {
   # Enables pointer compression for 8GB heaps.
   # Sets -DV8_COMPRESS_POINTERS_8GB.
   v8_enable_pointer_compression_8gb = ""
+
+  # Compile V8 using zlib as dependency.
+  # Sets -DV8_USE_ZLIB
+  v8_use_zlib = true
 }
 
 # Derived defaults.
@@ -622,6 +626,9 @@ if (v8_fuchsia_use_vmex_resource) {
   assert(target_os == "fuchsia", "VMEX resource only available on Fuchsia")
 }
 
+assert(!v8_enable_snapshot_compression || v8_use_zlib,
+       "Snapshot compression requires zlib")
+
 v8_random_seed = "314159265"
 v8_toolset_for_shell = "host"
 
@@ -1080,6 +1087,9 @@ config("features") {
   if (v8_enable_pointer_compression_8gb) {
     defines += [ "V8_COMPRESS_POINTERS_8GB" ]
   }
+  if (v8_use_zlib) {
+    defines += [ "V8_USE_ZLIB" ]
+  }
 }
 
 config("toolchain") {
@@ -3544,7 +3554,6 @@ v8_header_set("v8_internal_headers") {
     "src/snapshot/serializer.h",
     "src/snapshot/shared-heap-deserializer.h",
     "src/snapshot/shared-heap-serializer.h",
-    "src/snapshot/snapshot-compression.h",
     "src/snapshot/snapshot-data.h",
     "src/snapshot/snapshot-source-sink.h",
     "src/snapshot/snapshot-utils.h",
@@ -3607,6 +3616,10 @@ v8_header_set("v8_internal_headers") {
     "src/zone/zone.h",
   ]
 
+  if (v8_enable_snapshot_compression) {
+    sources += [ "src/snapshot/snapshot-compression.h" ]
+  }
+
   if (v8_use_perfetto) {
     sources -= [ "//base/trace_event/common/trace_event_common.h" ]
   }
@@ -4751,7 +4764,6 @@ v8_source_set("v8_base_without_compiler") {
     "src/snapshot/serializer.cc",
     "src/snapshot/shared-heap-deserializer.cc",
     "src/snapshot/shared-heap-serializer.cc",
-    "src/snapshot/snapshot-compression.cc",
     "src/snapshot/snapshot-data.cc",
     "src/snapshot/snapshot-source-sink.cc",
     "src/snapshot/snapshot-utils.cc",
@@ -4790,6 +4802,10 @@ v8_source_set("v8_base_without_compiler") {
     "src/zone/zone.cc",
   ]
 
+  if (v8_enable_snapshot_compression) {
+    sources += [ "src/snapshot/snapshot-compression.cc" ]
+  }
+
   if (v8_enable_maglev) {
     sources += [
       "src/maglev/maglev-code-generator.cc",
@@ -5226,10 +5242,12 @@ v8_source_set("v8_base_without_compiler") {
     ]
   }
 
-  deps += [
-    "//third_party/zlib",
-    "//third_party/zlib/google:compression_utils_portable",
-  ]
+  if (v8_use_zlib) {
+    deps += [
+      "//third_party/zlib",
+      "//third_party/zlib/google:compression_utils_portable",
+    ]
+  }
 
   if (v8_postmortem_support) {
     sources += [ "$target_gen_dir/debug-support.cc" ]

src/deoptimizer/translation-array.cc

@@ -7,13 +7,17 @@
 #include "src/base/vlq.h"
 #include "src/deoptimizer/translated-state.h"
 #include "src/objects/fixed-array-inl.h"
+
+#ifdef V8_USE_ZLIB
 #include "third_party/zlib/google/compression_utils_portable.h"
+#endif  // V8_USE_ZLIB
 
 namespace v8 {
 namespace internal {
 
 namespace {
 
+#ifdef V8_USE_ZLIB
 // Constants describing compressed TranslationArray layout. Only relevant if
 // --turbo-compress-translation-arrays is enabled.
 constexpr int kUncompressedSizeOffset = 0;
@@ -21,12 +25,14 @@ constexpr int kUncompressedSizeSize = kInt32Size;
 constexpr int kCompressedDataOffset =
     kUncompressedSizeOffset + kUncompressedSizeSize;
 constexpr int kTranslationArrayElementSize = kInt32Size;
+#endif  // V8_USE_ZLIB
 
 }  // namespace
 
 TranslationArrayIterator::TranslationArrayIterator(TranslationArray buffer,
                                                    int index)
     : buffer_(buffer), index_(index) {
+#ifdef V8_USE_ZLIB
   if (V8_UNLIKELY(FLAG_turbo_compress_translation_arrays)) {
     const int size = buffer_.get_int(kUncompressedSizeOffset);
     uncompressed_contents_.insert(uncompressed_contents_.begin(), size, 0);
@@ -41,9 +47,11 @@ TranslationArrayIterator::TranslationArrayIterator(TranslationArray buffer,
                  buffer_.DataSize()),
              Z_OK);
     DCHECK(index >= 0 && index < size);
-  } else {
-    DCHECK(index >= 0 && index < buffer.length());
+    return;
   }
+#endif  // V8_USE_ZLIB
+  DCHECK(!FLAG_turbo_compress_translation_arrays);
+  DCHECK(index >= 0 && index < buffer.length());
 }
 
 int32_t TranslationArrayIterator::Next() {
@@ -121,6 +129,7 @@ void TranslationArrayBuilder::AddDoubleRegister(DoubleRegister reg) {
 
 Handle<TranslationArray> TranslationArrayBuilder::ToTranslationArray(
     Factory* factory) {
+#ifdef V8_USE_ZLIB
   if (V8_UNLIKELY(FLAG_turbo_compress_translation_arrays)) {
     const int input_size = SizeInBytes();
     uLongf compressed_data_size = compressBound(input_size);
@@ -144,13 +153,14 @@ Handle<TranslationArray> TranslationArrayBuilder::ToTranslationArray(
                 compressed_data.data(), compressed_data_size);
 
     return result;
-  } else {
-    Handle<TranslationArray> result =
-        factory->NewByteArray(SizeInBytes(), AllocationType::kOld);
-    memcpy(result->GetDataStartAddress(), contents_.data(),
-           contents_.size() * sizeof(uint8_t));
-    return result;
   }
+#endif
+  DCHECK(!FLAG_turbo_compress_translation_arrays);
+  Handle<TranslationArray> result =
+      factory->NewByteArray(SizeInBytes(), AllocationType::kOld);
+  memcpy(result->GetDataStartAddress(), contents_.data(),
+         contents_.size() * sizeof(uint8_t));
+  return result;
 }
 
 void TranslationArrayBuilder::BeginBuiltinContinuationFrame(

src/flags/flag-definitions.h

@@ -957,8 +957,13 @@ DEFINE_BOOL(
     stress_gc_during_compilation, false,
     "simulate GC/compiler thread race related to https://crbug.com/v8/8520")
 DEFINE_BOOL(turbo_fast_api_calls, true, "enable fast API calls from TurboFan")
+#ifdef V8_USE_ZLIB
 DEFINE_BOOL(turbo_compress_translation_arrays, false,
             "compress translation arrays (experimental)")
+#else
+DEFINE_BOOL_READONLY(turbo_compress_translation_arrays, false,
+                     "compress translation arrays (experimental)")
+#endif  // V8_USE_ZLIB
 DEFINE_BOOL(turbo_inline_js_wasm_calls, true, "inline JS->Wasm calls")
 DEFINE_BOOL(turbo_use_mid_tier_regalloc_for_huge_functions, true,
             "fall back to the mid-tier register allocator for huge functions")

src/snapshot/snapshot-utils.cc

@@ -5,7 +5,10 @@
 #include "src/snapshot/snapshot-utils.h"
 
 #include "src/base/sanitizer/msan.h"
+
+#ifdef V8_USE_ZLIB
 #include "third_party/zlib/zlib.h"
+#endif
 
 namespace v8 {
 namespace internal {
@@ -16,9 +19,20 @@ uint32_t Checksum(base::Vector<const byte> payload) {
   // Mark every object as initialized in the code serializer.
   MSAN_MEMORY_IS_INITIALIZED(payload.begin(), payload.length());
 #endif  // MEMORY_SANITIZER
+
+#ifdef V8_USE_ZLIB
   // Priming the adler32 call so it can see what CPU features are available.
   adler32(0, nullptr, 0);
   return static_cast<uint32_t>(adler32(0, payload.begin(), payload.length()));
+#else
+  // Simple Fletcher-32.
+  uint32_t sum1 = 0, sum2 = 0;
+  for (auto data : payload) {
+    sum1 = (sum1 + data) % 65535;
+    sum2 = (sum2 + sum1) % 65535;
+  }
+  return (sum2 << 16 | sum1);
+#endif
 }
 
 }  // namespace internal

test/cctest/test-serialize.cc

@@ -437,6 +437,7 @@ static void SerializeContext(base::Vector<const byte>* startup_blob_out,
   v8_isolate->Dispose();
 }
 
+#ifdef SNAPSHOT_COMPRESSION
 UNINITIALIZED_TEST(SnapshotCompression) {
   DisableAlwaysOpt();
   base::Vector<const byte> startup_blob;
@@ -457,6 +458,7 @@ UNINITIALIZED_TEST(SnapshotCompression) {
   shared_space_blob.Dispose();
   context_blob.Dispose();
 }
+#endif  // SNAPSHOT_COMPRESSION
 
 UNINITIALIZED_TEST(ContextSerializerContext) {
   DisableAlwaysOpt();