On 21 February 2012 09:14, Ian Lance Taylor <iant@xxxxxxxxxx> wrote: > Ayonam Ray <ayonam@xxxxxxxxx> writes: > >> I have a set of built-ins implemented using unspec_volatile which set >> various processor control modes for rounding, overflow, etc. >> Now what I see is that if I call these builtins in between the >> arithmetic operations in C code, at -O1 and -O2, it puts together all >> those calls to the built-ins at the top of the function body and sends >> all the arithmetic operations below. Effectively, the arithmetic >> operations do not conform to the processor modes that I am setting. >> The same code works fine at -O0, i.e., the operations are not >> reordered (as expected). > > Your RTL is not expressing the dependencies between these instructions. > Using UNSPEC_VOLATILE doesn't prevent instructions from moving, it only > pevents them from being deleted. The usual way to express this would be > to have your process control insns set some fixed register and have your > match insns refer to that fixed register. By set and refer I only mean > in the RTL, not in the generated assembler code. > Ian, When you say UNSPEC_VOLATILE doesn't prevent instructions from moving, do you mean to say that such patterns will get reordered by the scheduler? Shafi
