31 lines
1.0 KiB
Plaintext
31 lines
1.0 KiB
Plaintext
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From: Chris Lattner [mailto:sabre@nondot.org]
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Sent: Wednesday, December 06, 2000 6:41 PM
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To: Vikram S. Adve
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Subject: Additional idea with respect to encoding
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Here's another idea with respect to keeping the common case instruction
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size down (less than 32 bits ideally):
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Instead of encoding an instruction to operate on two register numbers,
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have it operate on two negative offsets based on the current register
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number. Therefore, instead of using:
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r57 = add r55, r56 (r57 is the implicit dest register, of course)
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We could use:
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r57 = add -2, -1
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My guess is that most SSA references are to recent values (especially if
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they correspond to expressions like (x+y*z+p*q/ ...), so the negative
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numbers would tend to stay small, even at the end of the procedure (where
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the implicit register destination number could be quite large). Of course
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the negative sign is reduntant, so you would be storing small integers
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almost all of the time, and 5-6 bits worth of register number would be
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plenty for most cases...
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What do you think?
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-Chris
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