Re: [GHC] #14359: C-- pipeline/NCG fails to optimize simple repeated addition

17 Oct 2017

      #14359: C-- pipeline/NCG fails to optimize simple repeated addition
-------------------------------------+-------------------------------------
        Reporter:  bgamari           |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  low               |            Milestone:
       Component:  Compiler          |              Version:  8.2.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Runtime           |  Unknown/Multiple
  performance bug                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by alexbiehl):

 Actually compiling `PrimOps.cmm` with `-O` already results in the desired
 constant folding:

 {{{
 $ ghc -ddump-asm -c rts/PrimOps.cmm | less
 ...
 stg_newPinnedByteArrayzh:
 _cv:
         movq 888(%r13),%rax
         cmpq $0,16(%rax)
         je _cl
 _cn:
         movq g0@GOTPCREL(%rip),%rax
         movq (%rax),%rax
         movq 56(%rax),%rax
         movq large_alloc_lim@GOTPCREL(%rip),%rcx
         cmpq (%rcx),%rax
         jae _cl
 _co:
         subq $8,%rsp
         leaq -24(%r13),%rax
         leaq 38(%rbx),%rsi <- see here
         shrq $3,%rsi
         movq %rax,%rdi
         xorl %eax,%eax
         call allocatePinned
         addq $8,%rsp
         testq %rax,%rax
 ...
 }}}

-- 
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14359#comment:2
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