#1512: NCG to handle cyclic fixups for rematching register assignment for jump
blocks
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Reporter: guest | Owner:
Type: bug | Status: new
Priority: normal | Milestone:
Component: Compiler | Version:
Severity: normal | Resolution:
Keywords: | Difficulty: Moderate (1 day)
Os: Unknown | Testcase:
Architecture: Unknown |
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Comment (by guest):
I already considered xor swapping (that's why I restricted my claim to MOV
instructions). http://en.wikipedia.org/wiki/XOR_swap_algorithm advises
against using the XOR swap trick on modern CPUs and claims it'd be more
inefficient than a scratch location.
Also using pure swapping doesn't sound very appealing to me. Consider a
more complicated cycle involving more than just 2 nodes. The return value
of the SCC doesn't give you the cycle, but a set of nodes that contains a
cycle. It might contain leaves not involved in the cycle (as far as I
understood it). How would you swap (!InReg 1) with (!InReg 2 and !InMem
3)?
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/1512>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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