Revert "Remove all custom CopyCharsUnsigned implementations"

This reverts commit 5d8c4890.

Reason for revert: Fails on UBSan bot:
https://ci.chromium.org/p/v8/builders/ci/V8%20Linux64%20UBSan/7946

Original change's description:
> Remove all custom CopyCharsUnsigned implementations
> 
> It's unclear whether the custom implementation have any advantage over
> the standard library one's.
> Since we update our toolchain and standard library regularly, it might
> well be the case that the custom implementations are slower by now.
> 
> Thus this CL removes all {CopyCharsUnsigned} implementations and
> implements {CopyChars} generically using {std::copy_n}.
> 
> Note that this does not touch the {MemMove} and {MemCopy} functions
> yet, as we have seen regressions when trying to remove them before
> (https://crbug.com/v8/8675#c5).
> 
> R=​leszeks@chromium.org
> 
> Bug: v8:9396
> Change-Id: I97a183afebcccd2fbb567bdba02e827331475608
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1800577
> Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
> Reviewed-by: Leszek Swirski <leszeks@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#63808}

TBR=leszeks@chromium.org,clemensh@chromium.org

Change-Id: Ia16da942c7c28ba71076d1e3b0b8a6388a4ba359
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: v8:9396
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1806103Reviewed-by: Adam Klein <adamk@chromium.org>
Commit-Queue: Adam Klein <adamk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#63810}

src/builtins/arm/builtins-arm.cc

@@ -3167,6 +3167,51 @@ void Builtins::Generate_MemCopyUint8Uint8(MacroAssembler* masm) {
   __ Ret();
 }
 
+void Builtins::Generate_MemCopyUint16Uint8(MacroAssembler* masm) {
+  Register dest = r0;
+  Register src = r1;
+  Register chars = r2;
+
+  {
+    UseScratchRegisterScope temps(masm);
+
+    Register temp1 = r3;
+    Register temp2 = temps.Acquire();
+    Register temp3 = lr;
+    Register temp4 = r4;
+    Label loop;
+    Label not_two;
+
+    __ Push(lr, r4);
+    __ bic(temp2, chars, Operand(0x3));
+    __ add(temp2, dest, Operand(temp2, LSL, 1));
+
+    __ bind(&loop);
+    __ ldr(temp1, MemOperand(src, 4, PostIndex));
+    __ uxtb16(temp3, temp1);
+    __ uxtb16(temp4, temp1, 8);
+    __ pkhbt(temp1, temp3, Operand(temp4, LSL, 16));
+    __ str(temp1, MemOperand(dest));
+    __ pkhtb(temp1, temp4, Operand(temp3, ASR, 16));
+    __ str(temp1, MemOperand(dest, 4));
+    __ add(dest, dest, Operand(8));
+    __ cmp(dest, temp2);
+    __ b(&loop, ne);
+
+    __ mov(chars, Operand(chars, LSL, 31), SetCC);  // bit0 => ne, bit1 => cs
+    __ b(&not_two, cc);
+    __ ldrh(temp1, MemOperand(src, 2, PostIndex));
+    __ uxtb(temp3, temp1, 8);
+    __ mov(temp3, Operand(temp3, LSL, 16));
+    __ uxtab(temp3, temp3, temp1);
+    __ str(temp3, MemOperand(dest, 4, PostIndex));
+    __ bind(&not_two);
+    __ ldrb(temp1, MemOperand(src), ne);
+    __ strh(temp1, MemOperand(dest), ne);
+    __ Pop(pc, r4);
+  }
+}
+
 #undef __
 
 }  // namespace internal

src/builtins/builtins-definitions.h

@@ -1113,6 +1113,7 @@ namespace internal {
   TFS(SetProperty, kReceiver, kKey, kValue)                                    \
   TFS(SetPropertyInLiteral, kReceiver, kKey, kValue)                           \
   ASM(MemCopyUint8Uint8, CCall)                                                \
+  ASM(MemCopyUint16Uint8, CCall)                                               \
   ASM(MemMove, CCall)                                                          \
                                                                                \
   /* Trace */                                                                  \

src/builtins/builtins-internal-gen.cc

@@ -933,6 +933,12 @@ void Builtins::Generate_MemCopyUint8Uint8(MacroAssembler* masm) {
 }
 #endif  // !defined(V8_TARGET_ARCH_ARM) && !defined(V8_TARGET_ARCH_MIPS)
 
+#ifndef V8_TARGET_ARCH_ARM
+void Builtins::Generate_MemCopyUint16Uint8(MacroAssembler* masm) {
+  masm->Call(BUILTIN_CODE(masm->isolate(), Illegal), RelocInfo::CODE_TARGET);
+}
+#endif  // V8_TARGET_ARCH_ARM
+
 #ifndef V8_TARGET_ARCH_IA32
 void Builtins::Generate_MemMove(MacroAssembler* masm) {
   masm->Call(BUILTIN_CODE(masm->isolate(), Illegal), RelocInfo::CODE_TARGET);

src/parsing/scanner-character-streams.cc

@@ -265,7 +265,7 @@ class BufferedCharacterStream : public Utf16CharacterStream {
     }
 
     size_t length = Min(kBufferSize, range.length());
-    i::CopyChars(buffer_, range.start, length);
+    i::CopyCharsUnsigned(buffer_, range.start, length);
     buffer_end_ = &buffer_[length];
     return true;
   }

src/utils/memcopy.cc

@@ -25,8 +25,18 @@ V8_EXPORT_PRIVATE void MemMove(void* dest, const void* src, size_t size) {
   (*memmove_function)(dest, src, size);
 }
 #elif V8_OS_POSIX && V8_HOST_ARCH_ARM
+void MemCopyUint16Uint8Wrapper(uint16_t* dest, const uint8_t* src,
+                               size_t chars) {
+  uint16_t* limit = dest + chars;
+  while (dest < limit) {
+    *dest++ = static_cast<uint16_t>(*src++);
+  }
+}
+
 V8_EXPORT_PRIVATE MemCopyUint8Function memcopy_uint8_function =
     &MemCopyUint8Wrapper;
+MemCopyUint16Uint8Function memcopy_uint16_uint8_function =
+    &MemCopyUint16Uint8Wrapper;
 #elif V8_OS_POSIX && V8_HOST_ARCH_MIPS
 V8_EXPORT_PRIVATE MemCopyUint8Function memcopy_uint8_function =
     &MemCopyUint8Wrapper;
@@ -44,6 +54,9 @@ void init_memcopy_functions() {
     EmbeddedData d = EmbeddedData::FromBlob();
     memcopy_uint8_function = reinterpret_cast<MemCopyUint8Function>(
         d.InstructionStartOfBuiltin(Builtins::kMemCopyUint8Uint8));
+    memcopy_uint16_uint8_function =
+        reinterpret_cast<MemCopyUint16Uint8Function>(
+            d.InstructionStartOfBuiltin(Builtins::kMemCopyUint16Uint8));
   }
 #elif V8_OS_POSIX && V8_HOST_ARCH_MIPS
   if (Isolate::CurrentEmbeddedBlobIsBinaryEmbedded()) {