Improve generated MIPS code for conditional expressions and branches by delaying

runtime/vm/simulator_arm64.cc

 // Copyright (c) 2014, 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 <setjmp.h>
 #include <stdlib.h>
 
 #include "vm/globals.h"
 #if defined(TARGET_ARCH_ARM64)
 
 // Only build the simulator if not compiling for real ARM hardware.
 #if !defined(HOST_ARCH_ARM64)
 
 #include "vm/simulator.h"
 
 #include "vm/assembler.h"
 #include "vm/constants_arm64.h"
 #include "vm/disassembler.h"
 #include "vm/lockers.h"
 #include "vm/native_arguments.h"
 #include "vm/stack_frame.h"
 #include "vm/thread.h"
 
 namespace dart {
 
-DEFINE_FLAG(bool, trace_sim, false, "Trace simulator execution.");
-DEFINE_FLAG(int, stop_sim_at, 0,
+DEFINE_FLAG(int, trace_sim_after, -1,
+            "Trace simulator execution after instruction count reached.");
+DEFINE_FLAG(int, stop_sim_at, -1,
             "Instruction address or instruction count to stop simulator at.");
 
 
 // This macro provides a platform independent use of sscanf. The reason for
 // SScanF not being implemented in a platform independent way through
 // OS in the same way as SNPrint is that the Windows C Run-Time
 // Library does not provide vsscanf.
 #define SScanF sscanf  // NOLINT
 
 
@@ skipping 594 matching lines @@
         OS::Print("V flag: %d\n", sim_->v_flag_);
       } else if (strcmp(cmd, "unstop") == 0) {
         intptr_t stop_pc = sim_->get_pc() - Instr::kInstrSize;
         Instr* stop_instr = reinterpret_cast<Instr*>(stop_pc);
         if (stop_instr->IsExceptionGenOp()) {
           stop_instr->SetInstructionBits(Instr::kNopInstruction);
         } else {
           OS::Print("Not at debugger stop.\n");
         }
       } else if (strcmp(cmd, "trace") == 0) {
-        FLAG_trace_sim = !FLAG_trace_sim;
-        OS::Print("execution tracing %s\n", FLAG_trace_sim ? "on" : "off");
+        if (FLAG_trace_sim_after == -1) {
+          FLAG_trace_sim_after = sim_->get_icount();
+          OS::Print("execution tracing on\n");
+        } else {
+          FLAG_trace_sim_after = -1;
+          OS::Print("execution tracing off\n");
+        }
       } else if (strcmp(cmd, "bt") == 0) {
         PrintBacktrace();
       } else {
         OS::Print("Unknown command: %s\n", cmd);
       }
     }
     delete[] line;
   }
 
   // Add all the breakpoints back to stop execution and enter the debugger
@@ skipping 385 matching lines @@
 // Returns the top of the stack area to enable checking for stack pointer
 // validity.
 uword Simulator::StackTop() const {
   // To be safe in potential stack underflows we leave some buffer above and
   // set the stack top.
   return reinterpret_cast<uword>(stack_) +
       (Isolate::GetSpecifiedStackSize() + Isolate::kStackSizeBuffer);
 }
 
 
+bool Simulator::IsTracingExecution() const {
+  // Integer flag values are signed, so we must cast to unsigned.
+  // The default of -1 hence becomes the maximum unsigned value.
+  return (static_cast<uintptr_t>(icount_) >
+          static_cast<uintptr_t>(FLAG_trace_sim_after));
+}
+
+
 intptr_t Simulator::ReadX(uword addr, Instr* instr) {
   if ((addr & 7) == 0) {
     intptr_t* ptr = reinterpret_cast<intptr_t*>(addr);
     return *ptr;
   }
   UnalignedAccess("read", addr, instr);
   return 0;
 }
 
 
@@ skipping 491 matching lines @@
 typedef void (*SimulatorBootstrapNativeCall)(NativeArguments* arguments);
 typedef void (*SimulatorNativeCall)(NativeArguments* arguments, uword target);
 
 
 void Simulator::DoRedirectedCall(Instr* instr) {
   SimulatorSetjmpBuffer buffer(this);
   if (!setjmp(buffer.buffer_)) {
     int64_t saved_lr = get_register(LR);
     Redirection* redirection = Redirection::FromHltInstruction(instr);
     uword external = redirection->external_function();
-    if (FLAG_trace_sim) {
+    if (IsTracingExecution()) {
       OS::Print("Call to host function at 0x%" Pd "\n", external);
     }
 
     if ((redirection->call_kind() == kRuntimeCall) ||
         (redirection->call_kind() == kBootstrapNativeCall) ||
         (redirection->call_kind() == kNativeCall)) {
       // Set the top_exit_frame_info of this simulator to the native stack.
       set_top_exit_frame_info(reinterpret_cast<uword>(&buffer));
     }
     if (redirection->call_kind() == kRuntimeCall) {
@@ skipping 1694 matching lines @@
     DecodeFP(instr);
   } else {
     UnimplementedInstruction(instr);
   }
 }
 
 
 // Executes the current instruction.
 void Simulator::InstructionDecode(Instr* instr) {
   pc_modified_ = false;
-  if (FLAG_trace_sim) {
+  if (IsTracingExecution()) {
+    OS::Print("%"Pu64" ", icount_);
     const uword start = reinterpret_cast<uword>(instr);
     const uword end = start + Instr::kInstrSize;
     Disassembler::Disassemble(start, end);
   }
 
   if (instr->IsDPImmediateOp()) {
     DecodeDPImmediate(instr);
   } else if (instr->IsCompareBranchOp()) {
     DecodeCompareBranch(instr);
   } else if (instr->IsLoadStoreOp()) {
@@ skipping 184 matching lines @@
   set_register(NULL, kExceptionObjectReg, bit_cast<int64_t>(raw_exception));
   set_register(NULL, kStackTraceObjectReg, bit_cast<int64_t>(raw_stacktrace));
   buf->Longjmp();
 }
 
 }  // namespace dart
 
 #endif  // !defined(HOST_ARCH_ARM64)
 
 #endif  // defined TARGET_ARCH_ARM64