[Bug tree-optimization/65307] [4.9 Regression] Incorrect optimization breaks basic arithmetic

[maltsevm at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65307

Mikhail Maltsev <maltsevm at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |maltsevm at gmail dot com

--- Comment #8 from Mikhail Maltsev <maltsevm at gmail dot com> ---
A simpler testcase:

static inline unsigned cp(unsigned x)                                           
{                                                                               
    return x;                                                                   
}                                                                               

unsigned f(unsigned x)                                                          
{
    return cp(x * 2) * 2 + cp(cp(x * 2) * 3) * 5;
}

$ cat ./test1.c.085t.phiopt2

;; Function f (f, funcdef_no=1, decl_uid=1393, symbol_order=1)

f (unsigned int x)
{
  unsigned int _2;
  unsigned int _3;
  unsigned int _4;
  unsigned int _5;
  unsigned int _6;

  <bb 2>:
  _2 = x_1(D) * 2;
  _5 = 15;
  _3 = _5 + 2;
  _4 = _2 * _3;
  _6 = _4;
  return _6;

}

$ cat ./test1.c.087t.ccp3

;; Function f (f, funcdef_no=1, decl_uid=1393, symbol_order=1)


Pass statistics:
----------------

Immediate_uses: 

x_1(D) : --> single use.
_2 = x_1(D) * 2;

_2 : --> single use.
_4 = _2 * _3;

_3 : --> single use.
_4 = _2 * _3;

_4 : --> single use.
_6 = _4;

_5 : --> single use.
_3 = _5 + 2;

_6 : --> single use.
return _6;

.MEM_7(D) : --> single use.
# VUSE <.MEM_7(D)>
return _6;

Adding Destination of edge (0 -> 2) to worklist


Simulating block 2

Visiting statement:
# RANGE [0, 4294967295] NONZERO 0x000000000fffffffe
_2 = x_1(D) * 2;
which is likely CONSTANT
Lattice value changed to CONSTANT 0x00000000000000000 (0x000000000fffffffe). 
Adding SSA edges to worklist.

Visiting statement:
# RANGE [0, 4294967295] NONZERO 0x000000000fffffffe
_5 = 15;
which is likely CONSTANT
Lattice value changed to CONSTANT 14.  Adding SSA edges to worklist.

Visiting statement:
_3 = _5 + 2;
which is likely CONSTANT
Lattice value changed to CONSTANT 16.  Adding SSA edges to worklist.

Visiting statement:
_4 = _2 * _3;
which is likely CONSTANT
Lattice value changed to CONSTANT 0x00000000000000000 (0x000000000ffffffe0). 
Adding SSA edges to worklist.

Visiting statement:
# RANGE [0, 4294967295] NONZERO 0x000000000fffffffe
_6 = _4;
Lattice value changed to CONSTANT 0x00000000000000000 (0x000000000ffffffe0). 
Adding SSA edges to worklist.

Visiting statement:
# VUSE <.MEM_7(D)>
return _6;
No interesting values produced.  Marked VARYING.

Substituting values and folding statements

Folding statement: return _6;
Not folded
Folding statement: _6 = _4;
Not folded
Folding statement: _4 = _2 * _3;
Folded into: _4 = _2 * 16;

Removing dead stmt _3 = 16;

Removing dead stmt _5 = 14;

Folding statement: _2 = x_1(D) * 2;
Not folded

Pass statistics:
----------------
Constants propagated: 1
Statements deleted: 2

f (unsigned intD.4 xD.1392)
{
  unsigned intD.4 _2;
  unsigned intD.4 _4;
  unsigned intD.4 _6;

;;   basic block 2, loop depth 0, count 0, freq 10000, maybe hot
;;    prev block 0, next block 1, flags: (NEW, REACHABLE)
;;    pred:       ENTRY [100.0%]  (FALLTHRU,EXECUTABLE)
  # RANGE [0, 4294967295] NONZERO 0x000000000fffffffe
  _2 = x_1(D) * 2;
  # RANGE [0, 4294967295] NONZERO 0x000000000ffffffe0
  _4 = _2 * 16;
  # RANGE [0, 4294967295] NONZERO 0x000000000ffffffe0
  _6 = _4;
  # VUSE <.MEM_7(D)>
  return _6;
;;    succ:       EXIT [100.0%] 

}