Messages in this thread | | | Date | Fri, 22 Jan 1999 18:45:04 +0100 (CET) | From | Henrik Olsen <> | Subject | Re: Structure vs purism ? |
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On Fri, 22 Jan 1999, Thomas E. Dodd /CSDC wrote: > Stefan Monnier wrote: > > I think a lot of the goto's could be removed as soon as there is a decent > > possibility to tell the compiler to optimize for a certain case. This was > > discussed on the egcs lists some time ago IIRC. > > > > > compare against a final value because on most/many/(all?) processors > > > the flags change automatically when decrementing to zero or decrementing > > > to a negative number. > > > > MIPS and Alpha don't have `flags'. But I still agree that it's most of the > > time cheaper to check against 0 than against any other value. > > Then how do you get a beq or bne instruction? > There must be a status register that knows if > the last operation resulted in 0. > > The architecture coure I too was based on the MIPS. > We had a 0 bit from the ALU that could be checked. Simplest version is to make a true beq instruction to be something like beq <op1> <op2> <label> ie. branch if the operands are equal, some architectures even allows for additional hints for helping branch prediction
The beq you're talking about isn't a Branch if EQual at all, it's really a branch if zero-flag set, aliased for the normal use.
-- Henrik Olsen, Dawn Solutions I/S URL=http://www.iaeste.dk/~henrik/ Get the rest there.
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