FLD instruction x64 bit

Question

I have a little problem with FLD instruction in x64 bit ... want to load Double value to the stack pointer FPU in st0 register, but it seem to be impossible. In Delphi x32, I can use this code :

function DoSomething(X:Double):Double;
asm

  FLD    X
   // Do Something ..
  FST Result

end;

Unfortunately, in x64, the same code does not work.

Answer 1

Delphi inherite Microsoft x64 Calling Convention. So if arguments of function/procedure are float/double, they are passed in XMM0L, XMM1L, XMM2L, and XMM3L registers.

But you can use var before parameter as workaround like:

function DoSomething(var X:Double):Double;
asm
  FLD  qword ptr [X]
  // Do Something ..
  FST Result
end;