[tree-ssa-alias] tree-dse does not use pointer info

[xiangzhai]

Hi fellows,

Tom fixed PR67955 for gcc-7-branch, but gcc-6-branch is still able to reproduce the issue:

$ /opt/loongson-gnu-6/bin/mips64-linux-gnu-gcc -O2 -fno-tree-ccp -fno-tree-forwprop -fno-tree-fre -fdump-tree-dse1=/dev/stdout t.c

;; Function f (f, funcdef_no=0, decl_uid=1410, cgraph_uid=0, symbol_order=0)

f ()
{
  int * p;
  int a;
  int _5;

  <bb 2>:
  p_1 = &a;
  *p_1 = 1;
  a = 2;
  _5 = a;
  a ={v} {CLOBBER};
  return _5;

}

gcc 5.5 might not be effected:

$ /opt/loongson-gnu-5.5/bin/mips64-linux-gnu-gcc -O2 -fno-tree-ccp -fno-tree-forwprop -fno-tree-fre -fdump-tree-dse1=/dev/stdout t.c

;; Function f (f, funcdef_no=0, decl_uid=1485, cgraph_uid=0, symbol_order=0)

f ()
{
  int * p;
  int a;

  <bb 2>:
  a_6 = 1;
  a_4 = 2;
  a_5 = 2;
  return 2;

}

Regards,
Leslie Zhai

[xiangzhai]

Backported for gcc-6-branch:

$ /opt/loongson-gnu-6/bin/mips64-linux-gnu-gcc -O2 -fno-tree-ccp -fno-tree-forwprop -fno-tree-fre -fdump-tree-dse1-details=/dev/stdout t.c

;; Function f (f, funcdef_no=0, decl_uid=1410, cgraph_uid=0, symbol_order=0)

  Deleted dead store '*p_1 = 1;
'
f ()
{
  int * p;
  int a;
  int _5;

  <bb 2>:
  p_1 = &a;
  a = 2;
  _5 = a;
  a ={v} {CLOBBER};
  return _5;

}