[GHC] #14226: Common Block Elimination pass doesn't eliminate common blocks

13 Sep 2017

      #14226: Common Block Elimination pass doesn't eliminate common blocks
-------------------------------------+-------------------------------------
           Reporter:  bgamari        |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  high           |         Milestone:  8.4.1
          Component:  Compiler       |           Version:  8.2.1
  (CodeGen)                          |
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 In #14222 it was noted that something appears to be broken in
 `CmmCommonBlockElim`. Consider the program from that ticket,
 {{{#!hs
 module T14221 where

 import Data.Text as T

 isNumeric :: Text -> Bool
 isNumeric t =
     T.all isNumeric' t && T.any isNumber t
   where
     isNumber c = '0' <= c && c <= '9'
     isNumeric' c = isNumber c
                 || c == 'e'
                 || c == 'E'
                 || c == '.'
                 || c == '-'
                 || c == '+'
 }}}
 This program produces six copies of a block of the form,
 {{{#!c
       c6JT:
           R2 = I64[R1 + 7];
           R1 = P64[Sp + 8];
           Sp = Sp + 16;
           call $wloop_all_s6CQ_info(R2, R1) args: 8, res: 0, upd: 8;
 }}}
 in the `-ddump-opt-cmm` output, which are manifest in the assembler as,
 {{{#!asm
 block_c6JT_info:
 _c6JT:
         movq 7(%rbx),%r14
         movq 8(%rbp),%rbx
         addq $16,%rbp
         jmp $wloop_all_s6CQ_info
 }}}

 CBE really ought to be catching these.

-- 
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14226
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