https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113356

--- Comment #2 from Alex Coplan <acoplan at gcc dot gnu.org> ---
So we have this IR:

    insn i8 in bb2 [ebb2] at point 18:
      +----------------------------
      |    8: [r104:DI++]=r101:DI
      |      REG_DEAD r101:DI
      |      REG_INC r104:DI
      +----------------------------
      has pre/post-modify operations
      uses:
        use of set r101:i7 (DI pseudo)
        use of set r104:i17 (DI pseudo)
          appears in a read/write context
      defines:
        set r104:i8 (DI pseudo)
          set by a pre/post-modify
          appears in a read/write context
          used by insn i13 in bb2 [ebb2] at point 24
        set mem:i8

    insn i11 in bb2 [ebb2] at point 20:
      +------------------------------------------------
      |   11: r106:DI=high(const(`_ZTV6Class1'+0x10))
      +------------------------------------------------
      defines:
        set r106:i11 (DI pseudo)
          used by insn i12 in bb2 [ebb2] at point 22

    insn i12 in bb2 [ebb2] at point 22:
      +-------------------------------------------------------
      |   12: r105:DI=r106:DI+low(const(`_ZTV6Class1'+0x10))
      |      REG_DEAD r106:DI
      |      REG_EQUAL const(`_ZTV6Class1'+0x10)
      +-------------------------------------------------------
      uses:
        use of set r106:i11 (DI pseudo)
      defines:
        set r105:i12 (DI pseudo)
          used by insn i13 in bb2 [ebb2] at point 24

    insn i13 in bb2 [ebb2] at point 24:
      +----------------------------------------
      |   13: [r104:DI]=r105:DI
      |      REG_DEAD r105:DI
      |      REG_DEAD r104:DI
      |      REG_EH_REGION 0xffffffffffffffff
      +----------------------------------------
      uses:
        use of set r104:i8 (DI pseudo)
          appears inside an address
        use of set r105:i12 (DI pseudo)
      defines:
        set mem:i13
          used by phi node mem:a7 in ebb1 at point 30

and we're trying to form (8,13).  i8 has i13 as a hazard due to the writeback
dataflow and i13 has i12 as a hazard (due to the initial fix for non-call
exceptions introducing a hazard on the previous nondebug insn).  I wonder if it
would be enough to get i

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