[Bug rtl-optimization/48583] New: Mismatch between CFG and IR after cfglayout

["eraman at google dot com" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48583

           Summary: Mismatch between CFG and IR after cfglayout
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: eraman@google.com


Created attachment 23970
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=23970
RTL dump after into_cfglayout pass.

With gcc built from trunk revision 20110404,
$ trunk_gcc  -O2  gcc/testsuite/g++.dg/opt/nrv5.C  -fdump-rtl-all-all

In nrv5.C.149r.into_cfglayout, function 'void test(bool)' (_Z4testb) has the
following snippet:

;; Start of basic block ( 2) -> 4
;; Pred edge  2 [39.0%]  (fallthru)
(note 9 8 11 4 [bb 4] NOTE_INSN_BASIC_BLOCK)
(many RTL instructions)
(insn 37 36 40 4 (set (mem/s/j/c:QI (plus:DI (reg/f:DI 20 frame)
                (const_int -16 [0xfffffffffffffff0])) [0+0 S1 A64])
        (reg:QI 82)) nrv5.C:39 66 {*movqi_internal}
     (nil))
;; End of basic block 4 -> ( 6)

;; Succ edge  6 [100.0%]  (fallthru)

;; Start of basic block ( 2) -> 5
;; Pred edge  2 [61.0%] 
(code_label 40 37 41 5 21 "" [1 uses])

(note 41 40 43 5 [bb 5] NOTE_INSN_BASIC_BLOCK)


The last instruction in bb 4 is insn 37, which is not a jump. The successor
edge of bb 5 is 6 and is labeled a fallthru. But note that bb 5, and not bb 6,
follows insn 37.

In nrv5.C.148r.vregs, insn 37 is followed by a jump_insn which jumps to bb 6. 

The problem seems to be in try_redirect_by_replacing_jump in cfgrtl.c when
called from try_optimize_cfg in cfgcleanup.c. That seems to delete the jump
even though the successor edge is not a fallthru.