Reland^2 "Remove all custom CopyCharsUnsigned implementations"

This is an unmodified reland of
9febc505. Nosnap bots do not block
LKGR any more: https://crbug.com/v8/9737#c10.

Original change's description:
> Reland "Remove all custom CopyCharsUnsigned implementations"
>
> This is a reland of 5d8c4890
>
> 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}
>
> Bug: v8:9396
> Cq-Include-Trybots: luci.v8.try:v8_linux64_ubsan_rel_ng
> Change-Id: I9cd754ebe6b802bb4aabd6d2a448de41da040874
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1807357
> Reviewed-by: Leszek Swirski <leszeks@chromium.org>
> Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#63823}

TBR=leszeks@chromium.org

Bug: v8:9396
Change-Id: I793524d76b8b9c93d2a98c73e8d72967880fe1cf
Cq-Include-Trybots: luci.v8.try:v8_linux64_ubsan_rel_ng
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1809362
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#63857}

src/builtins/arm/builtins-arm.cc

@@ -3167,51 +3167,6 @@ 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

@@ -1110,7 +1110,6 @@ 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

@@ -932,12 +932,6 @@ 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::CopyCharsUnsigned(buffer_, range.start, length);
+    i::CopyChars(buffer_, range.start, length);
     buffer_end_ = &buffer_[length];
     return true;
   }

src/utils/memcopy.cc

@@ -25,18 +25,8 @@ 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;
@@ -54,9 +44,6 @@ 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()) {