[Bug tree-optimization/23297] New: immediate uses hosed after CCP

[rguenth at gcc dot gnu dot org]

With the attached patch applied, immuses get hosed during update_stmt while
propagating in ccp at tree-ssa-propagate.c:1154 (substitute_and_fold calling
mark_new_vars_to_rename).  Testcase:

struct B { int i; };

struct C { struct B c[1]; };

int e;
static struct C b;

void
foo (int d)
{
  struct C *x = &b;

  b.c[0].i = 424242;

  /* CCP destroys immuses of d */
  e = x->c[d].i;
}

we just have substituted &b into x and folded it to
D.1618_6 = bD.1612.cD.1610[dD.1613_5].iD.1608

update_stmt on this will remove the immediate use of dD.1613_5
which then DCE happily removes and we ICE in verify_ssa of it.

Just before CCP the trees look like

foo (dD.1613)
{
  struct C * xD.1616;
  intD.0 D.1618;
  intD.0 d.0D.1617;

  # BLOCK 0
  # PRED: ENTRY (fallthru)
  xD.1616_1 = &bD.1612;
  #   SFT.1D.1625_3 = V_MUST_DEF <SFT.1D.1625_2>;
  bD.1612.cD.1610[0].iD.1608 = 424242;
  dD.1613_5 = dD.1613_4;
  #   VUSE <SFT.1D.1625_3>;
  D.1618_6 = xD.1616_1->cD.1610[dD.1613_5].iD.1608;
  #   eD.1611_8 = V_MUST_DEF <eD.1611_7>;
  eD.1611 = D.1618_6;
  return;
  # SUCC: EXIT

}

with a single use of dD.1613_5.

-- 
           Summary: immediate uses hosed after CCP
           Product: gcc
           Version: 4.1.0
            Status: UNCONFIRMED
          Keywords: ice-on-valid-code
          Severity: normal
          Priority: P2
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: rguenth at gcc dot gnu dot org
                CC: gcc-bugs at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23297