Delphi's latest compiler provides a hint in these cases:

var

  x: Int32;

begin

  try

    x := 0;

    x := 1;

    writeln(x);

end.

[dcc32 Hint] Project1.dpr(14): H2077 Value assigned to 'x' never used

(Line 14 is the one assigning zero.)

---- On Thu, 09 Feb 2017 04:30:06 -0500 Tim Ward tdw@... [firebird-support] <firebird-support@yahoogroups.com> wrote ----

  It' the equivalent in a conventional programming language of saying:

x = a;

x = b;

where the compiler is expected to know that neither a not the first assignment have any side effects other than the assignment (and where the expression b doesn't depend on the value of x)(and where x isn't volatile, ect ect).

A compiler *could* detect and warn about such things (ie it's not forbidden by the laws of mathematics) but I don't think I know of any that do. And as there are good reasons for deliberately wanting to do the above it could only be a warning, not an error.

-- 
Tim Ward