src/cpu/x86/vm/macroAssembler_x86.cpp

rev 7609 : 8063086: Math.pow yields different results upon repeated calls
Summary: C2 treats x^2 as a special case and computes x * x while the interpreter and c1 don't have special case code for X^2.
Reviewed-by:

*** 3182,3192 ****
        ffree(1);
      }
      jmp(done);
    } else {
      // Stack: X Y
!     Label x_negative, y_odd;
  
      fldz();                     // Stack: 0 X Y
      fcmp(tmp, 1, true, false);  // Stack: X Y
      jcc(Assembler::above, x_negative);
  
--- 3182,3207 ----
        ffree(1);
      }
      jmp(done);
    } else {
      // Stack: X Y
!     Label x_negative, y_not_2;
! 
!     static double two = 2.0;
!     ExternalAddress two_addr((address)&two);
! 
!     fld_d(two_addr);            // Stack: 2 X Y
!     fcmp(tmp, 2, true, false);  // Stack: X Y
!     jcc(Assembler::parity, y_not_2);
!     jcc(Assembler::notEqual, y_not_2);
! 
!     fxch(); fpop();             // Stack: X
!     fmul(0);                    // Stack: X*X
!     
!     jmp(done);
! 
!     bind(y_not_2);
  
      fldz();                     // Stack: 0 X Y
      fcmp(tmp, 1, true, false);  // Stack: X Y
      jcc(Assembler::above, x_negative);