src/cpu/x86/vm/macroAssembler_x86.cpp

*** 7196,7220 ****
    }
  #endif
  
  }
  
! void MacroAssembler::clear_mem(Register base, Register cnt, Register tmp) {
    // cnt - number of qwords (8-byte words).
    // base - start address, qword aligned.
    assert(base==rdi, "base register must be edi for rep stos");
    assert(tmp==rax,   "tmp register must be eax for rep stos");
    assert(cnt==rcx,   "cnt register must be ecx for rep stos");
  
    xorptr(tmp, tmp);
    if (UseFastStosb) {
!     shlptr(cnt,3); // convert to number of bytes
      rep_stosb();
    } else {
!     NOT_LP64(shlptr(cnt,1);) // convert to number of dwords for 32-bit VM
      rep_stos();
    }
  }
  
  #ifdef COMPILER2
  
  // IndexOf for constant substrings with size >= 8 chars
--- 7196,7249 ----
    }
  #endif
  
  }
  
! void MacroAssembler::clear_mem(Register base, Register cnt, Register tmp, bool is_large) {
    // cnt - number of qwords (8-byte words).
    // base - start address, qword aligned.
+   // is_large - if optimizers know cnt is larger than InitArrayShortSize
    assert(base==rdi, "base register must be edi for rep stos");
    assert(tmp==rax,   "tmp register must be eax for rep stos");
    assert(cnt==rcx,   "cnt register must be ecx for rep stos");
+   assert(InitArrayShortSize % BytesPerLong == 0,
+     "InitArrayShortSize should be the multiple of BytesPerLong");
+ 
+   Label DONE;
    
    xorptr(tmp, tmp);
+ 
+   if (!is_large) {
+     Label LOOP, LONG;
+     cmpptr(cnt, InitArrayShortSize/BytesPerLong);
+     jccb(Assembler::greater, LONG);
+ 
+     NOT_LP64(shlptr(cnt, 1);) // convert to number of 32-bit words for 32-bit VM
+ 
+     decrement(cnt);
+     jccb(Assembler::negative, DONE); // Zero length
+             
+     // Use individual pointer-sized stores for small counts:
+     BIND(LOOP);
+     movptr(Address(base, cnt, Address::times_ptr), tmp);
+     decrement(cnt);
+     jccb(Assembler::greaterEqual, LOOP);
+     jmpb(DONE);
+     
+     BIND(LONG);
+   }
+ 
+   // Use longer rep-prefixed ops for non-small counts:
    if (UseFastStosb) {
!     shlptr(cnt, 3); // convert to number of bytes
      rep_stosb();
    } else {
!     NOT_LP64(shlptr(cnt, 1);) // convert to number of 32-bit words for 32-bit VM
      rep_stos();
    }
+ 
+   BIND(DONE);
  }
  
  #ifdef COMPILER2
  
  // IndexOf for constant substrings with size >= 8 chars