/*-----------------------------------------------------------------*/ 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); } } } }