Hello,
The purpose of the llvm.powi intrinsic isn't clear to me. Why is llvm.powi preferable to multiplication and division for small constant powers (e.g., 1/x, x*x, etc.)? Why is it preferable to llvm.pow for large variable powers? I'm also curious about the time bound. I'm assuming that powi(x,1000000) doesn't do a million multiplications... Do any architectures have an integer power instruction of some sort?
Regards,
Jon
The purpose of the llvm.powi intrinsic isn't clear to me. Why is
llvm.powi preferable to multiplication and division for small constant
powers (e.g., 1/x, x*x, etc.)? Why is it preferable to llvm.pow for
large variable powers? I'm also curious about the time bound. I'm
assuming that powi(x,1000000) doesn't do a million multiplications...
Do any architectures have an integer power instruction of some sort?
The purpose of this is to capture this information at a higher level, allowing the code generator top (eventually) lower it into an optimal sequence of multiplies. for example, powi(x, 9) can be lowered to:
t = x*x;
t2 = t*t
result = t2*t2*x
The code generator doesn't currently do any smart lowering, if you're interested in this, it would be a great place to dive in
-Chris
Do any architectures have an integer power instruction of some sort?
The purpose of this is to capture this information at a higher level,
allowing the code generator top (eventually) lower it into an optimal
"allowing the code generator to (eventually) lower it into an optimal"
-Chris
sequence of multiplies. for example, powi(x, 9) can be lowered to:
t = x*x;
t2 = t*t
result = t2*t2*xThe code generator doesn't currently do any smart lowering, if you're
interested in this, it would be a great place to dive in-Chris
-Chris