[GHC] #15188: Catch cases where both branches of an if jump to the same block.

26 May 2018


      #15188: Catch cases where both branches of an if jump to the same block.
-------------------------------------+-------------------------------------
           Reporter:  AndreasK       |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:  8.6.1
          Component:  Compiler       |           Version:  8.2.2
  (CodeGen)                          |
           Keywords:  CodeGen        |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 For one reason or the other sometimes we end up with if statements in Cmm
 where both branch targets are the same:

 Actual example from NoFib:
 {{{
        u9oL:
            if (_c9oA::P64 != 5) goto u9p2; else goto u9p2;
 }}}

 Which eventually results in this code:
 {{{
 _u9oL:
         cmpq $5,%rbx
         jne _u9p2 <- utterly pointless
 _u9p2:
         addq $16,%rbp
         jmp _c9iq
 }}}

-- 
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15188
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