I would like to add an example so as to clarify what it is that I seek help on: I have a custom implementation of a class called Number. Number has overloaded operators that write down a program of all computations that Number witnesses in an original program. For example, when the original program reads (original code): z=x-(-y); Then upon execution with type Number the following program will be produced (generated code) as caused through stream buffers in Number: tmp1 = -y; z = x-tmp1; This generated code is inferior to as if the original code had been "z=x+y;". Using expression templates or hoping for excellent compiler optimization on the "generated code", I could try to improve the performance of the generated code. But that means equal to re-inventing the wheel, because obviously the compilers have exactly these algebraic optimization capabilities already built in. So I want to use these capabilities. This is what my request is all about. Certainly the compiler has algebraic expression optimization built in, so what I now seek to find out is whether and how this can be leveraged outside the rule-scope of native c++, so as to improve the algebra of my original code. Of course I am aware that this alters the original programs result entirely (as per the above example) but this is precisely what I wish for. Kind regards In response to Segher: On Mon, Aug 26, 2024 at 7:19 PM Segher Boessenkool < segher@xxxxxxxxxxxxxxxxxxx> wrote: > On Mon, Aug 26, 2024 at 06:00:21PM +0200, Kai Song via Gcc-help wrote: > > I would like to learn more how GCC implements algebraic optimization > > heuristic such as given in -ffast-math . > > Thank you for responding. Yet I cannot make sense of your response or whether if how it relates to what I asked about. > Oh dear. > > > In particular, I have a type Number that is used in a code > > -ffast-math means you are not dealing with numbers at all, but instead > with quantities somewhat akin to numbers, and you don't give two hoots > about what happens with them. > Well if it was able to "deal" with anything akin to numbers, that would imply I can tell it to treat a type as if it was a number. Clearly however, that is not the case. So you may have meant something else, which is impossible to identify then due to ambiguity. This is unfortunate because I deeply care. So if you indeed mean that fastmath can be applied to anything akin to numbers, I am looking forward to how I can use the compilers abilities in that regard to transform algebraic expressions with custom types. > > It replaces floating point expressions by other expressions that are > at best vaguely related, and almost always compute a very different > result. > Yes, so here it is besides the question; because my custom type Number, which is the single point of interest in the communication, is not a floating point type. > > If you do not care about your numbers at all, and (against better > judgement) prefer more speed over all quality, you can use -ffast-math. > Well apparently I cannot, as per my question, since the algebraic expressions are involving my custom class Number. > Or, you can admit you think arithmetic is magic. It is fine to use > then, too. > I am a mathematician. I do not know nor wonder what you seek to say. I do care that arithmetic expressions are concise and equivalent. For instance, I like when "z=x-(-y);" is replaced by "z=x+y;" where x and y may be of type Number. > Segher >
