[Bug middle-end/61409] [4.9/5 regression] -Wmaybe-uninitialized false-positive with -O2

["manu at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61409

--- Comment #14 from Manuel López-Ibáñez <manu at gcc dot gnu.org> ---
And even simpler testcase:


void *init(void);

struct window
{
  int line_height;
  int pixel_width;
  int pixel_height;
  int column_width;
  int text_cols;
  int internal_border_width;
  int left_fringe_width, right_fringe_width;
} *rw;

void bar() __attribute__((noreturn));
void f(int i, int j) {
    void *ptr;
    if (i)
      {
        if (j)
          return; /* bar(); */
        ptr = init();
      }
    rw->pixel_width = ((rw->text_cols * (rw->column_width))
                       + (rw->left_fringe_width + (rw->right_fringe_width)) + 2
* (rw->internal_border_width));
  rw->pixel_height = ((rw->text_cols * (rw->line_height)));
  if (i)
    {
      rw=ptr;
    }
}


And the dump:

f (intD.6 iD.1843, intD.6 jD.1844)
{
  voidD.41 * ptrD.1847;
  struct window * rw.0_10;
  intD.6 _11;
  intD.6 _12;
  intD.6 _13;
  intD.6 _14;
  intD.6 _15;
  intD.6 _16;
  intD.6 _17;
  intD.6 _18;
  intD.6 _19;
  intD.6 _20;
  intD.6 _22;
  intD.6 _23;

;;   basic block 2, loop depth 0, count 0, freq 10000, maybe hot
;;    prev block 0, next block 9, flags: (NEW, REACHABLE)
;;    pred:       ENTRY [100.0%]  (FALLTHRU,EXECUTABLE)
;;   starting at line 17
  [test.c:17:8] if (i_4(D) != 0)
    goto <bb 3>;
  else
    goto <bb 9>;
;;    succ:       3 [50.0%]  (TRUE_VALUE,EXECUTABLE)
;;                9 [50.0%]  (FALSE_VALUE,EXECUTABLE)

;;   basic block 9, loop depth 0, count 0, freq 5000, maybe hot
;;    prev block 2, next block 3, flags: (NEW)
;;    pred:       2 [50.0%]  (FALSE_VALUE,EXECUTABLE)
;; 
  goto <bb 6>;
;;    succ:       6 [100.0%]  (FALLTHRU)

;;   basic block 3, loop depth 0, count 0, freq 5000, maybe hot
;;    prev block 9, next block 10, flags: (NEW, REACHABLE)
;;    pred:       2 [50.0%]  (TRUE_VALUE,EXECUTABLE)
;;   starting at line 19
  [test.c:19:5] if (j_7(D) != 0)
    goto <bb 10>;
  else
    goto <bb 5>;
;;    succ:       10 [61.0%]  (TRUE_VALUE,EXECUTABLE)
;;                5 [39.0%]  (FALSE_VALUE,EXECUTABLE)

;;   basic block 10, loop depth 0, count 0, freq 3051, maybe hot
;;    prev block 3, next block 4, flags: (NEW)
;;    pred:       3 [61.0%]  (TRUE_VALUE,EXECUTABLE)
;; 
;;    succ:       4 [100.0%]  (FALLTHRU)

;;   basic block 4, loop depth 0, count 0, freq 5761, maybe hot
;;    prev block 10, next block 5, flags: (NEW)
;;    pred:       10 [100.0%]  (FALLTHRU)
;;                11 [100.0%]  (FALLTHRU)
;; 
  # .MEM_47 = PHI <.MEM_6(D)(10), .MEM_24(11)>
  goto <bb 8>;
;;    succ:       8 [100.0%]  (FALLTHRU,EXECUTABLE)

;;   basic block 5, loop depth 0, count 0, freq 1949, maybe hot
;;    prev block 4, next block 6, flags: (NEW, REACHABLE)
;;    pred:       3 [39.0%]  (FALSE_VALUE,EXECUTABLE)
;;   starting at line 21
  [test.c:21:6] # .MEM_8 = VDEF <.MEM_6(D)>
  # PT = nonlocal escaped 
  # USE = nonlocal 
  # CLB = nonlocal 
  ptr_9 = initD.1831 ();
;;    succ:       6 [100.0%]  (FALLTHRU,EXECUTABLE)

;;   basic block 6, loop depth 0, count 0, freq 6949, maybe hot
;;    prev block 5, next block 11, flags: (NEW, REACHABLE)
;;    pred:       9 [100.0%]  (FALLTHRU)
;;                5 [100.0%]  (FALLTHRU,EXECUTABLE)
;;   starting at line 23
  # PT = nonlocal escaped 
  # ptr_1 = PHI <ptr_5(D)(9), [test.c:21:6] ptr_9(5)>
  # .MEM_2 = PHI <.MEM_6(D)(9), .MEM_8(5)>
  [test.c:23:27] # VUSE <.MEM_2>
  # PT = nonlocal escaped 
  rw.0_10 = rwD.1841;
  [test.c:23:27] # VUSE <.MEM_2>
  _11 = [test.c:23:27] rw.0_10->text_colsD.1837;
  [test.c:23:44] # VUSE <.MEM_2>
  _12 = [test.c:23:44] rw.0_10->column_widthD.1836;
  [test.c:23:39] _13 = _11 * _12;
  [test.c:24:15] # VUSE <.MEM_2>
  _14 = [test.c:24:15] rw.0_10->left_fringe_widthD.1839;
  [test.c:24:40] # VUSE <.MEM_2>
  _15 = [test.c:24:40] rw.0_10->right_fringe_widthD.1840;
  [test.c:24:35] _16 = _14 + _15;
  [test.c:24:10] _17 = _13 + _16;
  [test.c:24:72] # VUSE <.MEM_2>
  _18 = [test.c:24:72] rw.0_10->internal_border_widthD.1838;
  [test.c:24:67] # RANGE [-2147483648, 2147483647] NONZERO 4294967294
  _19 = _18 * 2;
  [test.c:24:63] _20 = _17 + _19;
  [test.c:23:21] # .MEM_21 = VDEF <.MEM_2>
  [test.c:23:7] rw.0_10->pixel_widthD.1834 = _20;
  [test.c:25:43] # VUSE <.MEM_21>
  _22 = [test.c:25:43] rw.0_10->line_heightD.1833;
  [test.c:25:38] _23 = _11 * _22;
  [test.c:25:20] # .MEM_24 = VDEF <.MEM_21>
  [test.c:25:5] rw.0_10->pixel_heightD.1835 = _23;
  [test.c:26:6] if (i_4(D) != 0)
    goto <bb 7>;
  else
    goto <bb 11>;
;;    succ:       7 [61.0%]  (TRUE_VALUE,EXECUTABLE)
;;                11 [39.0%]  (FALSE_VALUE,EXECUTABLE)

;;   basic block 11, loop depth 0, count 0, freq 2710, maybe hot
;;    prev block 6, next block 7, flags: (NEW)
;;    pred:       6 [39.0%]  (FALSE_VALUE,EXECUTABLE)
;; 
  goto <bb 4>;
;;    succ:       4 [100.0%]  (FALLTHRU)

;;   basic block 7, loop depth 0, count 0, freq 4239, maybe hot
;;    prev block 11, next block 8, flags: (NEW, REACHABLE)
;;    pred:       6 [61.0%]  (TRUE_VALUE,EXECUTABLE)
;;   starting at line 28
  [test.c:28:9] # .MEM_25 = VDEF <.MEM_24>
  rwD.1841 = ptr_1;
;;    succ:       8 [100.0%]  (FALLTHRU,EXECUTABLE)

;;   basic block 8, loop depth 0, count 0, freq 10000, maybe hot
;;    prev block 7, next block 1, flags: (NEW, REACHABLE)
;;    pred:       4 [100.0%]  (FALLTHRU,EXECUTABLE)
;;                7 [100.0%]  (FALLTHRU,EXECUTABLE)
;;   starting at line -1, discriminator 1
  # .MEM_3 = PHI <.MEM_47(4), .MEM_25(7)>
  # VUSE <.MEM_3>
  return;
;;    succ:       EXIT [100.0%] 

}

I don't really understand how the uninit pass computes the predicates, but when
replacing the "return" with "bar()", it is able to see that "j != 0" is not
part of the predicate guarding the def of ptr. Thus, somehow the analysis that
works for a noreturn function fails for a normal return.
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From: "law at redhat dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/65256] [5 regression] Undefined symbols linking f951
Date: Mon, 02 Mar 2015 19:36:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?ide256

Jeffrey A. Law <law at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |law at redhat dot com

--- Comment #1 from Jeffrey A. Law <law at redhat dot com> ---
John, is this with SOM or ELF?  If the former, it looks like something might be
missing its .import/.export statement.  What do the underlying symbols look
like for the reference and the definition of those symbols?