Partial update seems kind of odd

Article: Why Apple Won’t ARM the MacBook
By: Michael S (already5chosen.delete@this.yahoo.com), May 10, 2011 1:25 pm
Room: Moderated Discussions
Michael S (already5chosen@yahoo.com) on 5/10/11 wrote:
---------------------------
>Exophase (exophase@gmail.com) on 5/10/11 wrote:
>---------------------------
>>
>>Personally I never really liked the 4-flag model to begin with and would have preferred
>>a MIPS like flags-less model with "set" instructions (make predication work with
>>say, 3 registers), or possibly an SH-like model with one flag whose update depends on the instruction used.
>
>But on x86/ARM/MIPS a single comparison could serve several different conditional
>branches. Particularly useful for old Fortran's Arithmetic IF.
>

Sorry, bad example.
Of course, on MIPS and Alpha Fortran's Arithmetic IF could be just as successfully generated from a single comparison and two conditional branches.
The better case for arithmetic flags would be two branches (or conditional moves) based on the same the compare instruction with one of them doing signed comparison and other unsigned comparison.
I realize that it sounds rather artificial.

Another potential advantage for flags based scheme is that branch instruction doesn't have to specify a source register number so more space is left for other stuff.
Alpha solved this problem by brute force via using special "branch" instruction format. But in MIPS and clones (like, e.g. Altera Nios2) conditional branch is limited to +-32K instructions. More than enough for modular human-written code, but could be the problem for some cases of machine-generated code.
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                Partial update seems kind of oddExophase2011/05/10 08:51 AM
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