[Bug tree-optimization/21562] New: Quiet bad codegen (unrolling + tail call interaction)

[dalej at gcc dot gnu dot org]

Compile the following with -O2 -funroll-loops and you get bad codegen.  An uninitilaized value
is used as "pos" in computing the store address for mr[pos]=1 at the top of the function.  The
first dump where it's wrong seems to be "nrv".  If you unroll by hand it comes out correct.

extern int delta[8];
extern unsigned char board[421];

void
ping_recurse(int pos, int mr[400],  int color)
{
  int k;
  mr[pos] = 1;

  for (k = 0; k < 4; k++) {
    int apos = pos + delta[k];
    if (mr[apos] == 1 || board[apos] == color)
       ping_recurse(apos, mr, color);
  }
}

Beginning of codegen on darwin8:

_ping_recurse:
        mflr r0
        bcl 20,31,"L00000000001$pb"
"L00000000001$pb":
        stmw r28,-16(r1)
        mr r29,r4
        mflr r31
        mr r28,r5
        stw r0,8(r1)
        stwu r1,-80(r1)
L25:
        addis r11,r31,ha16(L_delta$non_lazy_ptr-"L00000000001$pb")
        slwi r2,r30,2   <<<< R30 uninitiailized

-- 
           Summary: Quiet bad codegen (unrolling + tail call interaction)
           Product: gcc
           Version: 4.0.0
            Status: UNCONFIRMED
          Keywords: wrong-code
          Severity: normal
          Priority: P2
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: dalej at gcc dot gnu dot org
                CC: gcc-bugs at gcc dot gnu dot org
 GCC build triplet: powerpc-apple-darwin8.0.0
  GCC host triplet: powerpc-apple-darwin8.0.0
GCC target triplet: powerpc-apple-darwin8.0.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21562