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There may well be. One alternative design that could have become the mainstream is VLIW. One of the features of VLIW is the idea of predication. Instead of a
by JdeBP 9y ago
There may well be. One alternative design that could have become the mainstream is VLIW. One of the features of VLIW is the idea of predication. Instead of a branch instruction altering the instruction fetch stream based upon the value of a flag bit in some form of condition code register, instruction syllables are encoded with predicates which simply control whether or not the instruction syllable has any effect, based upon the value of a flag bit in some form of predicate register.
VLIW is not a panacaea, engineering being all about tradeoffs after all. But it was intended to not have the complex instruction dispatching logic, with things like speculative execution and branch prediction, in the processor. Instead, using a process called if-conversion the compiler combines the two possible results of a conditional branch into a single instruction stream where predicates control which instruction syllables are executed.
* http://web.eecs.umich.edu/~mahlke/papers/1996/schlansker_hpl96.pdf http://web.eecs.umich.edu/~mahlke/papers/1996/schlansker_hpl...
* https://www.isi.edu/~youngcho/cse560m/vliw.pdf https://www.isi.edu/~youngcho/cse560m/vliw.pdf
* https://www.cse.umich.edu/awards/pdfs/p45-mahlke.pdf https://www.cse.umich.edu/awards/pdfs/p45-mahlke.pdf
* http://web.eecs.umich.edu/~mahlke/papers/1996/schlansker_hpl96.pdf http://web.eecs.umich.edu/~mahlke/papers/1996/schlansker_hpl...
Observe, in considering this alternative history, that the Itanium had 64 predicate registers. People have, in the past few days in various discussions of this subject, criticized Intel for holding on to a processor design for decades and prioritizing backwards compatibility over cleaner architecture. They have forgotten that Intel actually produced a cleaner architecture, back in the 1990s.