/*-----------------------------------------------------------------*/
int
killDeadCode (eBBlock ** ebbs, int count)
{
int change = 1;
int gchange = 0;
int i = 0;
/* basic algorithm :- */
/* first the exclusion rules :- */
/* 1. if result is a global or volatile then skip */
/* 2. if assignment and result is a temp & isaddr then skip */
/* since this means array & pointer access, will be taken */
/* care of by alias analysis. */
/* 3. if the result is used in the remainder of the block skip */
/* 4. if this definition does not reach the end of the block */
/* i.e. the result is not present in the outExprs then KILL */
/* 5. if it reaches the end of block & is used by some success */
/* or then skip */
/* else KILL */
/* this whole process is carried on iteratively till no change */
while (1)
{
change = 0;
/* for all blocks do */
for (i = 0; i < count; i++)
{
iCode *ic;
/* for all instructions in the block do */
for (ic = ebbs[i]->sch; ic; ic = ic->next)
{
int kill, j;
kill = 0;
if (SKIP_IC (ic) ||
ic->op == IFX ||
ic->op == RETURN)
continue;
/* if the result is volatile then continue */
if (IC_RESULT (ic) && isOperandVolatile (IC_RESULT (ic), FALSE))
continue;
/* if the result is a temp & isaddr then skip */
if (IC_RESULT (ic) && POINTER_SET (ic))
continue;
/* if the result is used in the remainder of the */
/* block then skip */
if (usedInRemaining (IC_RESULT (ic), ic->next))
continue;
/* does this definition reach the end of the block
or the usage is zero then we can kill */
if (!bitVectBitValue (ebbs[i]->outDefs, ic->key))
kill = 1; /* if not we can kill it */
else
{
/* if this is a global variable or function parameter */
/* we cannot kill anyway */
if (isOperandGlobal (IC_RESULT (ic)) ||
(OP_SYMBOL (IC_RESULT (ic))->_isparm &&
!OP_SYMBOL (IC_RESULT (ic))->ismyparm))
continue;
/* if we are sure there are no usages */
if (bitVectIsZero (OP_USES (IC_RESULT (ic))))
{
kill = 1;
goto kill;
}
/* reset visited flag */
for (j = 0; j < count; ebbs[j++]->visited = 0);
/* find out if this definition is alive */
if (applyToSet (ebbs[i]->succList,
isDefAlive,
ic))
continue;
kill = 1;
}
kill:
/* kill this one if required */
if (kill)
{
change = 1;
gchange++;
/* eliminate this */
remiCodeFromeBBlock (ebbs[i], ic);
/* now delete from defUseSet */
deleteItemIf (&ebbs[i]->outExprs, ifDiCodeIsX, ic);
bitVectUnSetBit (ebbs[i]->outDefs, ic->key);
/* and defset of the block */
bitVectUnSetBit (ebbs[i]->defSet, ic->key);
/* for the left & right remove the usage */
if (IS_SYMOP (IC_LEFT (ic)))
bitVectUnSetBit (OP_USES (IC_LEFT (ic)), ic->key);
if (IS_SYMOP (IC_RIGHT (ic)))
bitVectUnSetBit (OP_USES (IC_RIGHT (ic)), ic->key);
}
} /* end of all instructions */
if (!ebbs[i]->sch && !ebbs[i]->noPath)
disconBBlock (ebbs[i], ebbs, count);
} /* end of for all blocks */
if (!change)
break;
} /* end of while(1) */
return gchange;
}
/*-----------------------------------------------------------------*/
void
replaceSymBySym (set * sset, operand * src, operand * dest)
{
set *loop;
eBBlock *rBlock;
/* for all blocks in the set do */
for (loop = sset; loop; loop = loop->next)
{
iCode *ic;
rBlock = loop->item;
/* for all instructions in this block do */
for (ic = rBlock->sch; ic; ic = ic->next)
{
/* if we find usage */
if (ic->op == IFX && isOperandEqual (src, IC_COND (ic)))
{
bitVectUnSetBit (OP_USES (IC_COND (ic)), ic->key);
IC_COND (ic) = operandFromOperand (dest);
OP_USES(dest)=bitVectSetBit (OP_USES (dest), ic->key);
continue;
}
if (isOperandEqual (IC_RIGHT (ic), src))
{
bitVectUnSetBit (OP_USES (IC_RIGHT (ic)), ic->key);
IC_RIGHT (ic) = operandFromOperand (dest);
IC_RIGHT (ic)->isaddr = 0;
OP_USES(dest)=bitVectSetBit (OP_USES (dest), ic->key);
}
if (isOperandEqual (IC_LEFT (ic), src))
{
bitVectUnSetBit (OP_USES (IC_LEFT (ic)), ic->key);
if (POINTER_GET (ic) && IS_ITEMP (dest))
{
IC_LEFT (ic) = operandFromOperand (dest);
IC_LEFT (ic)->isaddr = 1;
}
else
{
IC_LEFT (ic) = operandFromOperand (dest);
IC_LEFT (ic)->isaddr = 0;
}
OP_USES(dest)=bitVectSetBit (OP_USES (dest), ic->key);
}
/* special case for pointer sets */
if (POINTER_SET (ic) &&
isOperandEqual (IC_RESULT (ic), src))
{
bitVectUnSetBit (OP_USES (IC_RESULT (ic)), ic->key);
IC_RESULT (ic) = operandFromOperand (dest);
IC_RESULT (ic)->isaddr = 1;
OP_USES(dest)=bitVectSetBit (OP_USES (dest), ic->key);
}
}
}
}
