[GHC] #10062: Codegen on sequential FFI calls is not very good

[GHC]

#10062: Codegen on sequential FFI calls is not very good
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        Reporter:  chadaustin        |                   Owner:
            Type:  bug               |                  Status:  new
        Priority:  normal            |               Milestone:
       Component:  Compiler          |                 Version:  7.8.3
  (CodeGen)                          |                Keywords:
      Resolution:                    |            Architecture:
Operating System:  Unknown/Multiple  |  Unknown/Multiple
 Type of failure:  Runtime           |               Test Case:
  performance bug                    |                Blocking:
      Blocked By:                    |  Differential Revisions:
 Related Tickets:                    |
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Comment (by rwbarton):

 > Change "movl $0,%eax" to "xorq %rax,%rax" (or maybe "movb $0,%al",
 though I don't know whether a smaller instruction is more important than
 breaking the data dependency on rax)

 This one is already implemented in GHC 7.10. (xor %eax,%eax is the
 Officially Correct instruction to use: it is the smallest instruction to
 clear a register and it has special processor support to break dependency
 chains, even though it looks like it doesn't).

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10062#comment:5>
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