Don't touch x18 on ARM64 - it is globally reserved on iOS.

runtime/vm/flow_graph_compiler.cc

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/globals.h"  // Needed here to get TARGET_ARCH_XXX.
 
 #include "vm/flow_graph_compiler.h"
 
 #include "vm/bit_vector.h"
 #include "vm/cha.h"
@@ skipping 1242 matching lines @@
   UNREACHABLE();
   return kNoRegister;
 }
 
 
 static uword RegMaskBit(Register reg) {
   return ((reg) != kNoRegister) ? (1 << (reg)) : 0;
 }
 
 
-// Mask of globally reserved registers. Some other registers are only reserved
-// in particular code (e.g., ARGS_DESC_REG in intrinsics).
-static const uword kReservedCpuRegisters = RegMaskBit(SPREG)
-                                         | RegMaskBit(FPREG)
-                                         | RegMaskBit(TMP)
-                                         | RegMaskBit(TMP2)
-                                         | RegMaskBit(PP)
-                                         | RegMaskBit(THR);
-
-
 void FlowGraphCompiler::AllocateRegistersLocally(Instruction* instr) {
   ASSERT(!is_optimizing());
 
   instr->InitializeLocationSummary(zone(),
                                    false);  // Not optimizing.
   LocationSummary* locs = instr->locs();
 
   bool blocked_registers[kNumberOfCpuRegisters];
 
-  // Mark all available registers free.
+  // Block all registers globally reserved by the assembler, etc and mark
+  // the rest as free.
   for (intptr_t i = 0; i < kNumberOfCpuRegisters; i++) {
-    blocked_registers[i] = false;
-  }
-
-  // Block all registers globally reserved by the assembler, etc.
-  for (intptr_t i = 0; i < kNumberOfCpuRegisters; i++) {
-    if ((kReservedCpuRegisters & (1 << i)) != 0) {
-      blocked_registers[i] = true;
-    }
+    blocked_registers[i] = (kDartAvailableCpuRegs & (1 << i)) == 0;
   }
 
   // Mark all fixed input, temp and output registers as used.
   for (intptr_t i = 0; i < locs->input_count(); i++) {
     Location loc = locs->in(i);
     if (loc.IsRegister()) {
       // Check that a register is not specified twice in the summary.
       ASSERT(!blocked_registers[loc.reg()]);
       blocked_registers[loc.reg()] = true;
     }
   }
 
   for (intptr_t i = 0; i < locs->temp_count(); i++) {
     Location loc = locs->temp(i);
     if (loc.IsRegister()) {
       // Check that a register is not specified twice in the summary.
       ASSERT(!blocked_registers[loc.reg()]);
       blocked_registers[loc.reg()] = true;
     }
   }
 
   if (locs->out(0).IsRegister()) {
     // Fixed output registers are allowed to overlap with
     // temps and inputs.
     blocked_registers[locs->out(0).reg()] = true;
   }
 
-  // Block all non-free registers.
-  for (intptr_t i = 0; i < kFirstFreeCpuRegister; i++) {
-    blocked_registers[i] = true;
-  }
-  for (intptr_t i = kLastFreeCpuRegister + 1; i < kNumberOfCpuRegisters; i++) {
-    blocked_registers[i] = true;
-  }
-
   // Allocate all unallocated input locations.
   const bool should_pop = !instr->IsPushArgument() && !instr->IsPushTemp();
   for (intptr_t i = locs->input_count() - 1; i >= 0; i--) {
     Location loc = locs->in(i);
     Register reg = kNoRegister;
     if (loc.IsRegister()) {
       reg = loc.reg();
     } else if (loc.IsUnallocated() || loc.IsConstant()) {
       ASSERT(loc.IsConstant() ||
              ((loc.policy() == Location::kRequiresRegister) ||
@@ skipping 238 matching lines @@
       reg_(kNoRegister),
       spilled_(false) {
   uword blocked_mask = RegMaskBit(blocked) | kReservedCpuRegisters;
   if (resolver->compiler_->intrinsic_mode()) {
     // Block additional registers that must be preserved for intrinsics.
     blocked_mask |= RegMaskBit(ARGS_DESC_REG);
   }
   reg_ = static_cast<Register>(
       resolver_->AllocateScratchRegister(Location::kRegister,
                                          blocked_mask,
-                                         kFirstFreeCpuRegister,
-                                         kLastFreeCpuRegister,
+                                         0,
+                                         kNumberOfCpuRegisters - 1,
                                          &spilled_));
 
   if (spilled_) {
     resolver->SpillScratch(reg_);
   }
 }
 
 
 ParallelMoveResolver::ScratchRegisterScope::~ScratchRegisterScope() {
   if (spilled_) {
@@ skipping 243 matching lines @@
 
 
 void FlowGraphCompiler::FrameStateClear() {
   ASSERT(!is_optimizing());
   frame_state_.TruncateTo(0);
 }
 #endif
 
 
 }  // namespace dart