[GHC] #2253: Native code generator could do better

[GHC]

#2253: Native code generator could do better
--------------------------------------+-------------------------------------
  Reporter:  dons                     |          Owner:                  
      Type:  bug                      |         Status:  new             
  Priority:  normal                   |      Milestone:  6.12 branch     
 Component:  Compiler (NCG)           |        Version:  6.8.2           
Resolution:                           |       Keywords:                  
Difficulty:  Unknown                  |             Os:  Unknown/Multiple
  Testcase:                           |   Architecture:  Unknown/Multiple
   Failure:  Runtime performance bug  |  
--------------------------------------+-------------------------------------
Changes (by morrow):

 * cc: morrow at moonpatio.com (added)

Comment:

 Replying to [comment:1 dons]:

 > == Program 6 ==
 {{{
 ..
   let c = replicateU n (2::Double)
 ..
 }}}

 > Native backend:
 {{{
   ..
   mulsd .LnZP(%rip),%xmm0   /*.LnZP==2.0*/
   addsd %xmm0,%xmm5
   ..
 }}}

 > C backend:
 {{{
   ..
   addsd       %xmm0, %xmm0
   addsd       %xmm0, %xmm5
   ..
 }}}


 Also, gcc is strength-reducing (2.0 * x) to (x + x).

 {{{
 MULSD mem64,xmmreg    ==> latency=6
 ADDSD xmmreg2,xmmreg1 ==> latency=4
 }}}

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/2253#comment:11>
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