A64: Relax the register constraints for LSeqStringGetChar.

src/a64/lithium-a64.cc

Index: src/a64/lithium-a64.cc
diff --git a/src/a64/lithium-a64.cc b/src/a64/lithium-a64.cc
index ab76044546d887eb119058b1fb9ba668236c4ffc..6106efc7538217389948875d12c9e63d4d4c129a 100644
--- a/src/a64/lithium-a64.cc
+++ b/src/a64/lithium-a64.cc
@@ -2014,11 +2014,8 @@ LInstruction* LChunkBuilder::DoReturn(HReturn* instr) {
 
 
 LInstruction* LChunkBuilder::DoSeqStringGetChar(HSeqStringGetChar* instr) {
-  // TODO(all): Use UseRegisterAtStart and UseRegisterOrConstantAtStart here.
-  // We cannot do it now because the debug code in the implementation changes
-  // temp.
-  LOperand* string = UseRegister(instr->string());
-  LOperand* index = UseRegisterOrConstant(instr->index());
+  LOperand* string = UseRegisterAtStart(instr->string());
+  LOperand* index = UseRegisterOrConstantAtStart(instr->index());
   LOperand* temp = TempRegister();
   LSeqStringGetChar* result =
       new(zone()) LSeqStringGetChar(string, index, temp);