Fix gc on MIPS (live registers were spilled in reversed order).

runtime/vm/flow_graph_compiler_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 "vm/globals.h"  // Needed here to get TARGET_ARCH_MIPS.
 #if defined(TARGET_ARCH_MIPS)
 
 #include "vm/flow_graph_compiler.h"
 
 #include "vm/ast_printer.h"
@@ skipping 1472 matching lines @@
     for (intptr_t reg_idx = 0; reg_idx < kNumberOfFpuRegisters; ++reg_idx) {
       DRegister fpu_reg = static_cast<DRegister>(reg_idx);
       if (locs->live_registers()->ContainsFpuRegister(fpu_reg)) {
         __ StoreDToOffset(fpu_reg, SP, offset);
         offset += kFpuRegisterSize;
       }
     }
     ASSERT(offset == (fpu_regs_count * kFpuRegisterSize));
   }
 
-  // Store general purpose registers with the lowest register number at the
-  // lowest address.
+  // Store general purpose registers with the highest register number at the
+  // lowest address. The order in which the registers are pushed must match the
+  // order in which the registers are encoded in the safe point's stack map.
   const intptr_t cpu_registers = locs->live_registers()->cpu_registers();
   ASSERT((cpu_registers & ~kAllCpuRegistersList) == 0);
   const int register_count = Utils::CountOneBits(cpu_registers);
-  int registers_pushed = 0;
-
-  __ addiu(SP, SP, Immediate(-register_count * kWordSize));
-  for (int i = 0; i < kNumberOfCpuRegisters; i++) {
-    Register r = static_cast<Register>(i);
-    if (locs->live_registers()->ContainsRegister(r)) {
-      __ sw(r, Address(SP, registers_pushed * kWordSize));
-      registers_pushed++;
+  if (register_count > 0) {
+    __ addiu(SP, SP, Immediate(-register_count * kWordSize));
+    intptr_t offset = register_count * kWordSize;
+    for (int i = 0; i < kNumberOfCpuRegisters; i++) {
+      Register r = static_cast<Register>(i);
+      if (locs->live_registers()->ContainsRegister(r)) {
+        offset -= kWordSize;
+        __ sw(r, Address(SP, offset));
+      }
     }

[koda, 2014/12/05 00:46:43]

ASSERT(offset == 0)?

[regis, 2014/12/05 00:56:11]

Done.

   }
 }
 
 
 void FlowGraphCompiler::RestoreLiveRegisters(LocationSummary* locs) {
-  // General purpose registers have the lowest register number at the
+  // General purpose registers have the highest register number at the
   // lowest address.
   __ TraceSimMsg("RestoreLiveRegisters");
   const intptr_t cpu_registers = locs->live_registers()->cpu_registers();
   ASSERT((cpu_registers & ~kAllCpuRegistersList) == 0);
   const int register_count = Utils::CountOneBits(cpu_registers);
-  int registers_popped = 0;
-
-  for (int i = 0; i < kNumberOfCpuRegisters; i++) {
-    Register r = static_cast<Register>(i);
-    if (locs->live_registers()->ContainsRegister(r)) {
-      __ lw(r, Address(SP, registers_popped * kWordSize));
-      registers_popped++;
+  if (register_count > 0) {
+    intptr_t offset = register_count * kWordSize;
+    for (int i = 0; i < kNumberOfCpuRegisters; i++) {
+      Register r = static_cast<Register>(i);
+      if (locs->live_registers()->ContainsRegister(r)) {
+        offset -= kWordSize;
+        __ lw(r, Address(SP, offset));
+      }
     }
+    __ addiu(SP, SP, Immediate(register_count * kWordSize));

[koda, 2014/12/05 00:46:43]

ASSERT(offset == 0)?

[regis, 2014/12/05 00:56:11]

Done.

   }
-  __ addiu(SP, SP, Immediate(register_count * kWordSize));
 
   const intptr_t fpu_regs_count = locs->live_registers()->FpuRegisterCount();
   if (fpu_regs_count > 0) {
     // Fpu registers have the lowest register number at the lowest address.
     intptr_t offset = 0;
     for (intptr_t reg_idx = 0; reg_idx < kNumberOfFpuRegisters; ++reg_idx) {
       DRegister fpu_reg = static_cast<DRegister>(reg_idx);
       if (locs->live_registers()->ContainsFpuRegister(fpu_reg)) {
         __ LoadDFromOffset(fpu_reg, SP, offset);
         offset += kFpuRegisterSize;
@@ skipping 294 matching lines @@
   __ AddImmediate(SP, kDoubleSize);
 }
 
 
 #undef __
 
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_MIPS