[assembler] Remove unconditional code target reservation

Some code - especially WebAssembly - does not make use of the code
target vector. Unconditionally reserving 100 entries adds unnecessary
overhead e.g. to jump table patching (~10%). This CL just removes this
reservation.

R=mstarzinger@chromium.org

Bug: v8:8916
Change-Id: I671820f3eb413fa2d03cef4bbf06adfc7a585266
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1559868Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60772}

src/arm64/assembler-arm64.cc

@@ -560,7 +560,6 @@ void Assembler::Reset() {
   memset(buffer_start_, 0, pc_ - buffer_start_);
 #endif
   pc_ = buffer_start_;
-  ReserveCodeTargetSpace(64);
   reloc_info_writer.Reposition(buffer_start_ + buffer_->size(), pc_);
   constpool_.Clear();
   next_constant_pool_check_ = 0;

src/assembler.cc

@@ -273,10 +273,6 @@ void AssemblerBase::UpdateCodeTarget(intptr_t code_target_index,
   code_targets_[code_target_index] = code;
 }
 
-void AssemblerBase::ReserveCodeTargetSpace(size_t num_of_code_targets) {
-  code_targets_.reserve(num_of_code_targets);
-}
-
 int Assembler::WriteCodeComments() {
   if (!FLAG_code_comments || code_comments_writer_.entry_count() == 0) return 0;
   int offset = pc_offset();

src/assembler.h

@@ -279,8 +279,6 @@ class V8_EXPORT_PRIVATE AssemblerBase : public Malloced {
   Handle<Code> GetCodeTarget(intptr_t code_target_index) const;
   // Update to the code target at {code_target_index} to {target}.
   void UpdateCodeTarget(intptr_t code_target_index, Handle<Code> target);
-  // Reserves space in the code target vector.
-  void ReserveCodeTargetSpace(size_t num_of_code_targets);
 
   // The buffer into which code and relocation info are generated.
   std::unique_ptr<AssemblerBuffer> buffer_;

src/s390/assembler-s390.cc

@@ -344,7 +344,6 @@ Assembler::Assembler(const AssemblerOptions& options,
                      std::unique_ptr<AssemblerBuffer> buffer)
     : AssemblerBase(options, std::move(buffer)) {
   reloc_info_writer.Reposition(buffer_start_ + buffer_->size(), pc_);
-  ReserveCodeTargetSpace(100);
   last_bound_pos_ = 0;
   relocations_.reserve(128);
 }

src/x64/assembler-x64.cc

@@ -428,7 +428,6 @@ bool Assembler::UseConstPoolFor(RelocInfo::Mode rmode) {
 Assembler::Assembler(const AssemblerOptions& options,
                      std::unique_ptr<AssemblerBuffer> buffer)
     : AssemblerBase(options, std::move(buffer)), constpool_(this) {
-  ReserveCodeTargetSpace(100);
   reloc_info_writer.Reposition(buffer_start_ + buffer_->size(), pc_);
   if (CpuFeatures::IsSupported(SSE4_1)) {
     EnableCpuFeature(SSSE3);