[GHC] #9425: ghc-HEAD (only in -O -fllvm aka 'optllvm') prunes yield in -fno-omit-yields mode

[GHC]

#9425: ghc-HEAD  (only in -O -fllvm aka 'optllvm') prunes yield in -fno-omit-
yields mode
-------------------------------------+-------------------------------------
       Reporter:  slyfox             |                   Owner:
           Type:  bug                |                  Status:  new
       Priority:  normal             |               Milestone:
      Component:  Compiler           |                 Version:  7.8.2
       Keywords:                     |        Operating System:
   Architecture:  Unknown/Multiple   |  Unknown/Multiple
     Difficulty:  Unknown            |         Type of failure:
     Blocked By:                     |  None/Unknown
Related Tickets:                     |               Test Case:
                                     |                Blocking:
                                     |  Differential Revisions:
-------------------------------------+-------------------------------------
 Found on '''./validate --slow''' today:

 {{{#!hs
 Unexpected failures:
    concurrent/should_run  T367_letnoescape [bad exit code] (optllvm)

 # run manually:
 $ LANG=C make fulltest stage=2 TEST=T367_letnoescape WAY=optllvm

 =====> T367_letnoescape(optllvm) 2419 of 4083 [0, 0, 0]
 cd ./concurrent/should_run && '/home/st/fun/ghc/inplace/bin/ghc-stage2'
 -fforce-recomp -dcore-lint -dcmm-lint -dno-debug-output -no-user-package-
 db -rtsopts -fno-ghci-history -o T367_letnoescape T367_letnoescape.hs -O
 -fllvm -fno-omit-yields  >T367_letnoescape.comp.stderr 2>&1
 cd ./concurrent/should_run && ./T367_letnoescape    </dev/null
 >T367_letnoescape.run.stdout 2>T367_letnoescape.run.stderr
 Timeout happened...killing process...
 Wrong exit code (expected 0 , actual 99 )
 Stdout:

 Stderr:

 *** unexpected failure for T367_letnoescape(optllvm)
 }}}

 I've loaded test in gdb and manually interrupted it:
 {{{
 ^C
 Program received signal SIGINT, Interrupt.
 0x0000000000407110 in r5Wp_info ()
 (gdb) disassemble
 Dump of assembler code for function r5Wp_info:
    0x00000000004070f8 <+0>:     mov    0x358(%r13),%rax
    0x00000000004070ff <+7>:     dec    %r14
    0x0000000000407102 <+10>:    data32 data32 data32 data32 nopw
 %cs:0x0(%rax,%rax,1)

 => 0x0000000000407110 <+24>:    inc    %r14
    0x0000000000407113 <+27>:    test   %rax,%rax
    0x0000000000407116 <+30>:    jne    0x407110 <r5Wp_info+24>

    0x0000000000407118 <+32>:    mov    -0x8(%r13),%rax
    0x000000000040711c <+36>:    mov    $0x8e0690,%ebx
    0x0000000000407121 <+41>:    jmpq   *%rax
 End of assembler dump
 }}}

 Here we see 3 instructions-long dead loop.

 llvm-3.4.2, amd64-linux.

 Looks like yield code was not emitted or was moved away.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9425>
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