[Bug c/30785] Test to null pointer optimised away at -O2

[etienne_lorrain at yahoo dot fr]

------- Comment #2 from etienne_lorrain at yahoo dot fr  2007-02-13 13:44 
-------
 Problem is fixed by -fno-tree-vrp and -O2
 I am not a specialist of -fdump-tree-all, but it seems like that:
 tmp.c.t35.copyprop1:

;; Function strncpy (strncpy)

strncpy (pDest, pSrc, n)
{
  char * D.1282;
  char * D.1281;

<bb 0>:
  if (pDest_2 == 0B) goto <L1>; else goto <L0>;

<L0>:;
  if (pSrc_5 == 0B) goto <L1>; else goto <L4>;

<L1>:;
  if (pDest_2 != 0B) goto <L2>; else goto <L3>;

<L2>:;
  *pDest_2 = 0;

<L3>:;
  pDest_4 = pDest_2;
  goto <bb 6> (<L5>);

<L4>:;
  pDest_7 = xxcpy (pDest_2, pSrc_5, n_6);
  pDest_8 = pDest_7;

  # pDest_1 = PHI <pDest_2(4), pDest_7(5)>;
<L5>:;
  return pDest_1;

}
-------------------
  tmp.t36.vrp, the test disappear:

;; Function strncpy (strncpy)


SSA replacement table
N_i -> { O_1 ... O_j } means that N_i replaces O_1, ..., O_j

pDest_12 -> { pDest_2 }
pDest_13 -> { pDest_2 }
pDest_14 -> { pDest_2 }
pDest_15 -> { pDest_2 }
pSrc_16 -> { pSrc_5 }

Number of virtual NEW -> OLD mappings:       0
Number of real NEW -> OLD mappings:          5
Number of total NEW -> OLD mappings:         5

Number of virtual symbols: 0


Incremental SSA update started at block: 0

Number of blocks in CFG: 9
Number of blocks to update: 9 (100%)




Value ranges after VRP:

pDest_1: VARYING
pDest_2: ~[0B, 0B]  EQUIVALENCES: { } (0 elements)
<retval>_3: VARYING
pSrc_5: ~[0B, 0B]  EQUIVALENCES: { } (0 elements)
pDest_7: VARYING
pDest_8: [pDest_7, pDest_7]  EQUIVALENCES: { pDest_7 } (1 elements)
pDest_15: ~[0B, 0B]  EQUIVALENCES: { pDest_2 } (1 elements)
pSrc_16: ~[0B, 0B]  EQUIVALENCES: { pSrc_5 } (1 elements)


Folding predicate pDest_2 == 0B to 0
Folding predicate pSrc_5 == 0B to 0
Folding predicate pDest_2 != 0B to 1
Removing basic block 7
Removing basic block 2
Removing basic block 8
Removing basic block 3
Removing basic block 4
Removing basic block 1
Merging blocks 0 and 5
Merging blocks 0 and 6
strncpy (pDest, pSrc, n)
{
  char * D.1282;
  char * D.1281;

<bb 0>:
  pDest_7 = xxcpy (pDest_2, pSrc_5, n_6);
  pDest_8 = pDest_7;
  return pDest_7;

}

  Thanks,
  Etienne.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30785