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References: <bug-44069-17521@http.gcc.gnu.org/bugzilla/>
Subject: [Bug middle-end/44069] [4.5 Regression] optimization bug initializing from cast array
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From: "rguenth at gcc dot gnu dot org" <gcc-bugzilla@gcc.gnu.org>
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------- Comment #5 from rguenth at gcc dot gnu dot org  2010-05-12 20:16 -------
So, the issue is that the loop copying vals to m looks like

<bb 3>:
  D.21310_23 = r_22 * 4;
  D.21309_25 = D.21310_23 + c_24;
  D.21308_26 = (long unsigned int) D.21309_25;
  D.21305_29 = vals[0][D.21308_26];
  m.m[D.21309_25] = D.21305_29;
  c_30 = c_24 + 1;

<bb 4>:
  # c_24 = PHI <c_32(7), c_30(3)>
  if (c_24 <= 3)
    goto <bb 3>;
  else
    goto <bb 5>;

<bb 5>:
  r_31 = r_22 + 1;

<bb 6>:
  # r_22 = PHI <0(2), r_31(5)>
  if (r_22 <= 3)
    goto <bb 7>;
  else
    goto <bb 8>;

<bb 7>:
  # c_32 = PHI <0(6)>
  goto <bb 4>;

where vals[0][D.21308_26] does not represent a use of vals[i][j] with
i > 0.  This is because get_ref_base_and_extent restricts the valid
extent of D.21308_26 to 3.  Note that the issue is exposed by
re-constructing an array-reference from the pointer access in the
inlined constructor.  After inlining into main() we have

<bb 3>:
  D.21310_23 = r_22 * 4;
  D.21309_25 = D.21310_23 + c_24;
  D.21308_26 = (long unsigned int) D.21309_25;
  D.21307_27 = D.21308_26 * 8;
  D.21306_28 = &vals[0][D.21308_26];
  D.21305_29 = *D.21306_28;
  m.m[D.21309_25] = D.21305_29;
  c_30 = c_24 + 1;

from the non-inlined variant

<bb 4>:
  D.21286_7 = r_1 * 4;
  D.21287_8 = D.21286_7 + c_2;
  D.21286_9 = r_1 * 4;
  D.21287_10 = D.21286_9 + c_2;
  D.21288_11 = (long unsigned int) D.21287_10;
  D.21289_12 = D.21288_11 * 8;
  D.21290_14 = arr_13(D) + D.21289_12;
  D.21291_15 = *D.21290_14;
  this_16(D)->m[D.21287_10] = D.21291_15;
  c_17 = c_2 + 1;


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|c++                         |middle-end
           Keywords|                            |wrong-code
            Summary|optimization bug            |[4.5 Regression]
                   |initializing from cast array|optimization bug
                   |                            |initializing from cast array
   Target Milestone|---                         |4.5.1


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44069