Revert "[regalloc] add hint for operands in gap moves."

This reverts commit c14b3e4d.

Reason for revert: https://crbug.com/1335195

Original change's description:
> [regalloc] add hint for operands in gap moves.
>
> To eliminate unnecessary move instructions from register to fixed register. We check the fixed register hint for operands in move gaps
> when building LiveRanges. If a to_operand has a hint_operand (with fixed register), then set the hint_operand for from_operand too. This can avoid the register allocator ignore hint information about fixed register.
>
> Bug: v8:12909
> Change-Id: I17f9afa484ee08de8ac1ab42945caba2c362fc9e
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3669019
> Reviewed-by: Thibaud Michaud <thibaudm@chromium.org>
> Commit-Queue: Jialu Zhang <jialu.zhang@intel.com>
> Cr-Commit-Position: refs/heads/main@{#80844}

Bug: v8:12909
Change-Id: Iedba9244a75074e448c5e85880cc202866b91e71
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3702335
Commit-Queue: Thibaud Michaud <thibaudm@chromium.org>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/heads/main@{#81126}

src/compiler/backend/register-allocator.cc

@@ -220,13 +220,6 @@ bool UsePosition::HintRegister(int* register_code) const {
   UNREACHABLE();
 }
 
-InstructionOperand* UsePosition::GetHintOperand() const {
-  if (HintTypeField::decode(flags_) == UsePositionHintType::kOperand) {
-    return reinterpret_cast<InstructionOperand*>(hint_);
-  }
-  return nullptr;
-}
-
 UsePositionHintType UsePosition::HintTypeForOperand(
     const InstructionOperand& op) {
   switch (op.kind()) {
@@ -2321,20 +2314,6 @@ void LiveRangeBuilder::ProcessInstructions(const InstructionBlock* block,
               cur->Eliminate();
               continue;
             }
-            // Check if to_operand already has a hint_operand(with fixed
-            // register), if true, set the hint_operand for from_operand to
-            // avoid this important hint information be ignored by register
-            // allocator.
-            int hint_reg = kUnassignedRegister;
-            UsePosition* hint_pos = to_range->FirstHintPosition(&hint_reg);
-            if (hint_pos != nullptr) {
-              DCHECK_NE(hint_reg, kUnassignedRegister);
-              InstructionOperand* hint_operand = hint_pos->GetHintOperand();
-              if (hint_operand->IsAnyLocationOperand()) {
-                hint = hint_operand;
-                hint_type = UsePosition::HintTypeForOperand(*hint_operand);
-              }
-            }
           }
         } else {
           Define(curr_position, &to, spill_mode);

src/compiler/backend/register-allocator.h

@@ -502,7 +502,6 @@ class V8_EXPORT_PRIVATE UsePosition final
   bool IsResolved() const {
     return hint_type() != UsePositionHintType::kUnresolved;
   }
-  InstructionOperand* GetHintOperand() const;
   static UsePositionHintType HintTypeForOperand(const InstructionOperand& op);
 
  private: