Fix an occasional crash in Assembler::ldr() for arm.

A peephole optimization can be attempted on a buffer that contains only a single command. The crash happens when running debug on Snow Leopard with --simulator=arm.

Review URL: http://codereview.chromium.org/2454001

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@4762 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/arm/assembler-arm.cc

@@ -1213,12 +1213,11 @@ void Assembler::ldr(Register dst, const MemOperand& src, Condition cond) {
   // Both instructions can be eliminated if ry = rx.
   // If ry != rx, a register copy from ry to rx is inserted
   // after eliminating the push and the pop instructions.
+  if (can_peephole_optimize(2)) {
     Instr push_instr = instr_at(pc_ - 2 * kInstrSize);
     Instr pop_instr = instr_at(pc_ - 1 * kInstrSize);
 
-  if (can_peephole_optimize(2) &&
-      IsPush(push_instr) &&
-      IsPop(pop_instr)) {
+    if (IsPush(push_instr) && IsPop(pop_instr)) {
       if ((pop_instr & kRdMask) != (push_instr & kRdMask)) {
         // For consecutive push and pop on different registers,
         // we delete both the push & pop and insert a register move.
@@ -1230,7 +1229,8 @@ void Assembler::ldr(Register dst, const MemOperand& src, Condition cond) {
         // Insert a mov instruction, which is better than a pair of push & pop
         mov(reg_popped, reg_pushed);
         if (FLAG_print_peephole_optimization) {
-        PrintF("%x push/pop (diff reg) replaced by a reg move\n", pc_offset());
+          PrintF("%x push/pop (diff reg) replaced by a reg move\n",
+                 pc_offset());
         }
       } else {
         // For consecutive push and pop on the same register,
@@ -1241,6 +1241,7 @@ void Assembler::ldr(Register dst, const MemOperand& src, Condition cond) {
         }
       }
     }
+  }
 
   if (can_peephole_optimize(2)) {
     Instr str_instr = instr_at(pc_ - 2 * kInstrSize);