Print one line when pushing an immediate followed by a pop is

src/assembler-ia32.cc

 // Copyright (c) 1994-2006 Sun Microsystems Inc.
 // All Rights Reserved.
 //
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions
 // are met:
 //
 // - Redistributions of source code must retain the above copyright notice,
 // this list of conditions and the following disclaimer.
 //
@@ skipping 457 matching lines @@
     } else if (instr == 0x6a && dst.is(eax)) {  // push of immediate 8 bit
       byte imm8 = last_pc_[1];
       if (imm8 == 0) {
         // 6a00         push 0x0
         // 58           pop eax
         last_pc_[0] = 0x31;
         last_pc_[1] = 0xc0;
         // change to
         // 31c0         xor eax,eax
         last_pc_ = NULL;
+        if (FLAG_print_push_pop_elimination) {
+          PrintF("%d push/pop (imm->reg) eliminated\n", pc_offset());
+        }
         return;
       } else {
         // 6a00         push 0xXX
         // 58           pop eax
         last_pc_[0] = 0xb8;
         EnsureSpace ensure_space(this);
         if ((imm8 & 0x80) != 0) {
           EMIT(0xff);
           EMIT(0xff);
           EMIT(0xff);
           // change to
           // b8XXffffff   mov eax,0xffffffXX
         } else {
           EMIT(0x00);
           EMIT(0x00);
           EMIT(0x00);
           // change to
           // b8XX000000   mov eax,0x000000XX
         }
         last_pc_ = NULL;
+        if (FLAG_print_push_pop_elimination) {
+          PrintF("%d push/pop (imm->reg) eliminated\n", pc_offset());
+        }
         return;
       }
     } else if (instr == 0x68 && dst.is(eax)) {  // push of immediate 32 bit
       // 68XXXXXXXX   push 0xXXXXXXXX
       // 58           pop eax
       last_pc_[0] = 0xb8;
       last_pc_ = NULL;
       // change to
       // b8XXXXXXXX   mov eax,0xXXXXXXXX
+      if (FLAG_print_push_pop_elimination) {
+        PrintF("%d push/pop (imm->reg) eliminated\n", pc_offset());
+      }
       return;
     }
 
     // Other potential patterns for peephole:
     // 0x712716   102  890424         mov [esp], eax
     // 0x712719   105  8b1424         mov edx, [esp]
   }
   EnsureSpace ensure_space(this);
   last_pc_ = pc_;
   EMIT(0x58 | dst.code());
@@ skipping 1504 matching lines @@
   ASSERT(bound_label.is_bound());
   ASSERT(0 <= position);
   ASSERT(position + static_cast<int>(sizeof(uint32_t)) <= pc_offset());
   ASSERT(long_at(position) == 0);  // only initialize once!
 
   uint32_t label_loc = reinterpret_cast<uint32_t>(addr_at(bound_label.pos()));
   long_at_put(position, label_loc);
 }
 
 } }  // namespace v8::internal