[Bug tree-optimization/39529] New: ICE on valid code

[edmar at freescale dot com]

The compiler gives ICE on valid code.



Invocation:

gcc -O3 -S x.c



Test case:

void
foo (void)
{
  char a[1024];
  char *p = &a[0];
  char *p2;

  p2 = p + 1024;
  do
    {
      p += 2;
      *(p-2) = 1;
      *(p-1) = 1;
    } while (p < p2);
}



Output:

x.c: In function 'foo':
x.c:3: error: missing definition
for SSA_NAME: SMT.9_14 in statement:
SMT.9_8 = PHI <SMT.9_10(D)(2), SMT.9_14(4)>
PHI argument
SMT.9_14
for PHI node
SMT.9_8 = PHI <SMT.9_10(D)(2), SMT.9_14(4)>
x.c:3: internal compiler error: verify_ssa failed



Description:

Bellow is x.c.106t.vect for target PowerPC 603e, but the same ICE
happens for altivec and for x86_64. The vectorizer replaces the two
original stores with one vector store, leaving behind a bad SMT phi
node.


Pass statistics:
----------------
Vectorized loops: 1

Merging blocks 2 and 6
foo ()
{
  unsigned intD.3 ivtmp.31D.1297;
  vector charD.1 * ivtmp.30D.1296;
  vector charD.1 * vect_pa.29D.1295;
  vector charD.1 * vect_pa.25D.1291;
  vector charD.1 vect_cst_.24D.1290;
  unsigned intD.3 ivtmp.23D.1283;
  charD.1 * p2D.1254;
  charD.1 * pD.1253;
  charD.1 aD.1252[1024];
  charD.1 * D.1258;

  # BLOCK 2 freq:100
  # PRED: ENTRY [100.0%]  (fallthru,exec)
  p2D.1254_3 = &aD.1252 + 1024;
  vect_cst_.24D.1290_18 = { 1, 1, 1, 1 };
  vect_pa.29D.1295_19 = (vector charD.1 *) &aD.1252;
  vect_pa.25D.1291_20 = vect_pa.29D.1295_19;
  # SUCC: 3 [100.0%]  (fallthru)

  # BLOCK 3 freq:10000
  # PRED: 2 [100.0%]  (fallthru) 4 [100.0%]  (fallthru,dfs_back,exec)
  # ivtmp.31D.1297_23 = PHI <0(2), ivtmp.31D.1297_24(4)>
  # ivtmp.30D.1296_21 = PHI <vect_pa.25D.1291_20(2), ivtmp.30D.1296_22(4)>
  # ivtmp.23D.1283_16 = PHI <512(2), ivtmp.23D.1283_17(4)>
  # SMT.9D.1269_8 = PHI <SMT.9D.1269_10(D)(2), SMT.9D.1269_14(4)>
  # =============================================================
  # aD.1252_7 = PHI <aD.1252_9(D)(2), aD.1252_25(4)>
  # pD.1253_1 = PHI <&aD.1252(2), pD.1253_4(4)>
  pD.1253_4 = pD.1253_1 + 2;
  # aD.1252_25 = VDEF <aD.1252_7> { aD.1252 }
  *ivtmp.30D.1296_21 = vect_cst_.24D.1290_18;
  D.1258_6 = pD.1253_4 + -1;
  ivtmp.23D.1283_17 = ivtmp.23D.1283_16 - 1;
  ivtmp.30D.1296_22 = ivtmp.30D.1296_21 + 4;
  ivtmp.31D.1297_24 = ivtmp.31D.1297_23 + 1;
  if (ivtmp.31D.1297_24 < 256)
    goto <bb 4>;
  else
    goto <bb 5>;
  # SUCC: 4 [99.0%]  (true,exec) 5 [1.0%]  (false,exec)

  # BLOCK 4 freq:9900
  # PRED: 3 [99.0%]  (true,exec)
  goto <bb 3>;
  # SUCC: 3 [100.0%]  (fallthru,dfs_back,exec)

  # BLOCK 5 freq:100
  # PRED: 3 [1.0%]  (false,exec)
  return;
  # SUCC: EXIT [100.0%]

}



My solution:

After each loop is vectorized, and SSA is updated, I re-compute alias
info. I am not familiar with the vectorizer sources, so I don't know
if there is a more efficient way to fix this problem, and still be
sure it would be correct for all inputs.

This attached patch fixed the problem for 603e, altivec, and
x86_64. Regression tests done for 603e and it is under way for x86_64.


-- 
           Summary: ICE on valid code
           Product: gcc
           Version: 4.4.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: edmar at freescale dot com
 GCC build triplet: powerpc-unknown-linux-gnu
  GCC host triplet: powerpc-unknown-linux-gnu
GCC target triplet: powerpc-unknown-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39529