Improve generated MIPS code for conditional expressions and branches by delaying

runtime/vm/simulator_mips.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 <setjmp.h>
 #include <stdlib.h>
 
 #include "vm/globals.h"
 #if defined(TARGET_ARCH_MIPS)
 
 // Only build the simulator if not compiling for real MIPS hardware.
 #if !defined(HOST_ARCH_MIPS)
 
 #include "vm/simulator.h"
 
 #include "vm/assembler.h"
 #include "vm/constants_mips.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 547 matching lines @@
         }
       } 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->IsBreakPoint()) {
           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 374 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));
+}
+
+
 void Simulator::Format(Instr* instr, const char* format) {
   OS::PrintErr("Simulator - unknown instruction: %s\n", format);
   UNIMPLEMENTED();
 }
 
 
 int8_t Simulator::ReadB(uword addr) {
   int8_t* ptr = reinterpret_cast<int8_t*>(addr);
   return *ptr;
 }
@@ skipping 194 matching lines @@
     SimulatorDebugger dbg(this);
     const char* message = *reinterpret_cast<const char**>(
         reinterpret_cast<intptr_t>(instr) - Instr::kInstrSize);
     set_pc(get_pc() + Instr::kInstrSize);
     dbg.Stop(instr, message);
     // Adjust for extra pc increment.
     set_pc(get_pc() - Instr::kInstrSize);
   } else if (instr->BreakCodeField() == Instr::kSimulatorMessageCode) {
     const char* message = *reinterpret_cast<const char**>(
         reinterpret_cast<intptr_t>(instr) - Instr::kInstrSize);
-    if (FLAG_trace_sim) {
+    if (IsTracingExecution()) {
       OS::Print("Message: %s\n", message);
-    } else {
-      OS::PrintErr("Bad break code: 0x%x\n", instr->InstructionBits());
-      UnimplementedInstruction(instr);
     }
   } else if (instr->BreakCodeField() == Instr::kSimulatorRedirectCode) {
     SimulatorSetjmpBuffer buffer(this);
 
     if (!setjmp(buffer.buffer_)) {
       int32_t saved_ra = get_register(RA);
       Redirection* redirection = Redirection::FromBreakInstruction(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 730 matching lines @@
         OS::PrintErr("DecodeCop1: 0x%x\n", instr->InstructionBits());
         UnimplementedInstruction(instr);
         break;
       }
     }
   }
 }
 
 
 void Simulator::InstructionDecode(Instr* instr) {
-  if (FLAG_trace_sim) {
+  if (IsTracingExecution()) {
+    OS::Print("%u ", icount_);
     const uword start = reinterpret_cast<uword>(instr);
     const uword end = start + Instr::kInstrSize;
     Disassembler::Disassemble(start, end);
   }
 
   switch (instr->OpcodeField()) {
     case SPECIAL: {
       DecodeSpecial(instr);
       break;
     }
@@ skipping 278 matching lines @@
   }
   pc_ += Instr::kInstrSize;
 }
 
 
 void Simulator::ExecuteDelaySlot() {
   ASSERT(pc_ != kEndSimulatingPC);
   delay_slot_ = true;
   icount_++;
   Instr* instr = Instr::At(pc_ + Instr::kInstrSize);
-  if (FLAG_stop_sim_at != 0) {
+  if (FLAG_stop_sim_at != -1) {
     if (static_cast<int>(icount_) == FLAG_stop_sim_at) {
       SimulatorDebugger dbg(this);
       dbg.Stop(instr, "Instruction count reached");
     } else if (reinterpret_cast<int>(instr) == FLAG_stop_sim_at) {
       SimulatorDebugger dbg(this);
       dbg.Stop(instr, "Instruction address reached");
     }
   }
   InstructionDecode(instr);
   delay_slot_ = false;
 }
 
 
 void Simulator::Execute() {
-  if (FLAG_stop_sim_at == 0) {
+  if (FLAG_stop_sim_at == -1) {
     // Fast version of the dispatch loop without checking whether the simulator
     // should be stopping at a particular executed instruction.
     while (pc_ != kEndSimulatingPC) {
       icount_++;
       Instr* instr = Instr::At(pc_);
       if (IsIllegalAddress(pc_)) {
         HandleIllegalAccess(pc_, instr);
       } else {
         InstructionDecode(instr);
       }
@@ skipping 181 matching lines @@
   set_register(kExceptionObjectReg, bit_cast<int32_t>(raw_exception));
   set_register(kStackTraceObjectReg, bit_cast<int32_t>(raw_stacktrace));
   buf->Longjmp();
 }
 
 }  // namespace dart
 
 #endif  // !defined(HOST_ARCH_MIPS)
 
 #endif  // defined TARGET_ARCH_MIPS