1 /*-------------------------------------------------------------------------
3 SDCCcflow.c - source file for control flow analysis
5 Written By - Sandeep Dutta . sandeep.dutta@usa.net (1998)
7 This program is free software; you can redistribute it and/or modify it
8 under the terms of the GNU General Public License as published by the
9 Free Software Foundation; either version 2, or (at your option) any
12 This program is distributed in the hope that it will be useful,
13 but WITHOUT ANY WARRANTY; without even the implied warranty of
14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 GNU General Public License for more details.
17 You should have received a copy of the GNU General Public License
18 along with this program; if not, write to the Free Software
19 Foundation, 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
21 In other words, you are welcome to use, share and improve this program.
22 You are forbidden to forbid anyone else to use, share and improve
23 what you give them. Help stamp out software-hoarding!
24 -------------------------------------------------------------------------*/
28 /*-----------------------------------------------------------------*/
29 /* domSetFromVect - creates a domset from the vector */
30 /*-----------------------------------------------------------------*/
32 domSetFromVect (eBBlock ** ebbs, bitVect * domVect)
40 for (i = 0; i < domVect->size; i++)
41 if (bitVectBitValue (domVect, i))
42 addSet (&domSet, ebbs[i]);
47 /*-----------------------------------------------------------------*/
48 /* addSuccessor - will add bb to succ also add it to the pred of */
50 /*-----------------------------------------------------------------*/
52 addSuccessor (eBBlock * thisBlock, eBBlock * succ)
54 /* check for boundary conditions */
55 if (!thisBlock || !succ)
58 /* add it to the succ of thisBlock */
59 addSetIfnotP (&thisBlock->succList, succ);
62 bitVectSetBit (thisBlock->succVect, succ->bbnum);
63 /* add this edge to the list of edges */
64 addSet (&graphEdges, newEdge (thisBlock, succ));
68 /*-----------------------------------------------------------------*/
69 /* eBBPredecessors - find the predecessors for each block */
70 /*-----------------------------------------------------------------*/
72 eBBPredecessors (eBBlock ** ebbs, int count)
76 /* for each block do */
77 for (i = 0; i < count; i++)
80 /* if there is no path to this then continue */
84 /* for each successor of this block if */
85 /* it has depth first number > this block */
86 /* then this block precedes the successor */
87 for (j = 0; j < ebbs[i]->succVect->size; j++)
89 if (bitVectBitValue (ebbs[i]->succVect, j) &&
90 ebbs[j]->dfnum > ebbs[i]->dfnum)
92 addSet (&ebbs[j]->predList, ebbs[i]);
96 /*-----------------------------------------------------------------*/
97 /* eBBSuccessors- find out the successors of all the nodes */
98 /*-----------------------------------------------------------------*/
100 eBBSuccessors (eBBlock ** ebbs, int count)
104 /* for all the blocks do */
105 for (; i < count; i++)
112 ebbs[i]->succVect = newBitVect (count);
114 /* if the next on exists & this one does not */
115 /* end in a GOTO or RETURN then the next is */
116 /* a natural successor of this. Note we have */
117 /* consider eBBlocks with no instructions */
123 if (ebbs[i]->ech->op != GOTO &&
124 ebbs[i]->ech->op != RETURN &&
125 ebbs[i]->ech->op != JUMPTABLE)
129 while (ebbs[j] && ebbs[j]->noPath)
132 addSuccessor (ebbs[i], ebbs[j]); /* add it */
134 } /* no instructions in the block */
135 /* could happen for dummy blocks */
137 addSuccessor (ebbs[i], ebbs[i + 1]);
140 /* go thru all the instructions: if we find a */
141 /* goto or ifx or a return then we have a succ */
142 if ((ic = ebbs[i]->ech))
146 /* special case for jumptable */
147 if (ic->op == JUMPTABLE)
150 for (lbl = setFirstItem (IC_JTLABELS (ic)); lbl;
151 lbl = setNextItem (IC_JTLABELS (ic)))
152 addSuccessor (ebbs[i],
153 eBBWithEntryLabel (ebbs, lbl, count));
159 /* depending on the instruction operator */
162 case GOTO: /* goto has edge to label */
163 succ = eBBWithEntryLabel (ebbs, ic->argLabel.label, count);
166 case IFX: /* conditional jump */
167 /* if true label is present */
169 succ = eBBWithEntryLabel (ebbs, IC_TRUE (ic), count);
171 succ = eBBWithEntryLabel (ebbs, IC_FALSE (ic), count);
174 case RETURN: /* block with return */
175 succ = eBBWithEntryLabel (ebbs, returnLabel, count);
179 /* if there is a successor add to the list */
180 /* if it is not already present in the list */
182 addSuccessor (ebbs[i], succ);
188 /*-----------------------------------------------------------------*/
189 /* computeDominance - computes the dominance graph */
190 /* for algorithm look at Dragon book section 10.10, algo 10.16 */
191 /*-----------------------------------------------------------------*/
193 computeDominance (eBBlock ** ebbs, int count)
197 /* now do the initialisation */
198 /* D(n0) := { n0 } */
200 bitVectSetBit (ebbs[0]->domVect = newBitVect (count), ebbs[0]->bbnum);
203 /* for n in N - { n0 } do D(n) = N */
204 for (i = 1; i < count; i++)
206 ebbs[i]->domVect = newBitVect (count);
207 for (j = 0; j < count; j++)
210 bitVectSetBit (ebbs[i]->domVect, ebbs[j]->bbnum);
214 /* end of initialisation */
216 /* while changes to any D(n) occur do */
217 /* for n in N - { n0 } do */
218 /* D(n) := { n } U (intersection of D( all predecessors of n)) */
224 for (i = 1; i < count; i++)
231 /* get the intersection of the dominance of all predecessors */
232 for (pred = setFirstItem (ebbs[i]->predList),
233 cDomVect = (pred ? bitVectCopy (pred->domVect) : NULL);
235 pred = setNextItem (ebbs[i]->predList))
237 cDomVect = bitVectIntersect (cDomVect, pred->domVect);
240 cDomVect = newBitVect (count);
241 /* this node to the list */
242 cDomVect = bitVectSetBit (cDomVect, ebbs[i]->bbnum);
245 if (!bitVectEqual (cDomVect, ebbs[i]->domVect))
247 ebbs[i]->domVect = cDomVect;
252 /* if no change then exit */
258 /*-----------------------------------------------------------------*/
259 /* immedDom - returns the immediate dominator of a block */
260 /*-----------------------------------------------------------------*/
262 immedDom (eBBlock ** ebbs, eBBlock * ebp)
264 /* first delete self from the list */
265 set *iset = domSetFromVect (ebbs, ebp->domVect);
267 eBBlock *idom = NULL;
269 deleteSetItem (&iset, ebp);
270 /* then just return the one with the greatest */
271 /* depthfirst number, this will be the immed dominator */
272 if ((loop = setFirstItem (iset)))
274 for (; loop; loop = setNextItem (iset))
275 if (loop->dfnum > idom->dfnum)
278 setToNull ((void **) &iset);
283 /*-----------------------------------------------------------------*/
284 /* DFOrdering - is visited then nothing else call DFOrdering this */
285 /*-----------------------------------------------------------------*/
286 DEFSETFUNC (DFOrdering)
288 eBBlock *ebbp = item;
289 V_ARG (int *, count);
294 computeDFOrdering (ebbp, count); /* depthfirst */
299 /*-----------------------------------------------------------------*/
300 /* computeDFOrdering - computes the depth first ordering of the */
302 /*-----------------------------------------------------------------*/
304 computeDFOrdering (eBBlock * ebbp, int *count)
308 /* for each successor that is not visited */
309 applyToSet (ebbp->succList, DFOrdering, count);
311 /* set the depth first number */
312 ebbp->dfnum = *count;
316 /*-----------------------------------------------------------------*/
317 /* disconBBlock - removes all control flow links for a block */
318 /*-----------------------------------------------------------------*/
320 disconBBlock (eBBlock * ebp, eBBlock ** ebbs, int count)
322 /* mark this block as noPath & recompute control flow */
324 computeControlFlow (ebbs, count, TRUE);
327 /*-----------------------------------------------------------------*/
328 /* markNoPath - marks those blocks which cannot be reached from top */
329 /*-----------------------------------------------------------------*/
331 markNoPath (eBBlock ** ebbs, int count)
336 /* for all blocks if the visited flag is not set : then there */
337 /* is no path from _entry to this block push them down in the */
338 /* depth first order */
339 for (i = 0; i < count; i++)
340 if (!ebbs[i]->visited)
343 /*-----------------------------------------------------------------*/
344 /* dfNumCompare - used by qsort to sort by dfNumber */
345 /*-----------------------------------------------------------------*/
347 dfNumCompare (const void *a, const void *b)
349 const eBBlock *const *i = a;
350 const eBBlock *const *j = b;
352 if ((*i)->dfnum > (*j)->dfnum)
355 if ((*i)->dfnum < (*j)->dfnum)
361 /*-----------------------------------------------------------------*/
362 /* bbNumCompare - used by qsort to sort by bbNumber */
363 /*-----------------------------------------------------------------*/
365 bbNumCompare (const void *a, const void *b)
367 const eBBlock *const *i = a;
368 const eBBlock *const *j = b;
370 if ((*i)->bbnum > (*j)->bbnum)
373 if ((*i)->bbnum < (*j)->bbnum)
380 /*-----------------------------------------------------------------*/
381 /* computeControlFlow - does the control flow computation */
382 /*-----------------------------------------------------------------*/
384 computeControlFlow (eBBlock ** ebbs, int count, int reSort)
386 int saveCount = count;
389 /* initialise some things */
391 for (i = 0; i < count; i++)
393 setToNull ((void **) &ebbs[i]->predList);
394 setToNull ((void **) &ebbs[i]->domVect);
395 setToNull ((void **) &ebbs[i]->succList);
396 setToNull ((void **) &ebbs[i]->succVect);
397 ebbs[i]->visited = 0;
402 /* sort it back by block number */
403 qsort (ebbs, saveCount, sizeof (eBBlock *), bbNumCompare);
405 setToNull ((void **) &graphEdges);
406 /* this will put in the */
407 /* successor information for each blk */
408 eBBSuccessors (ebbs, count);
410 /* compute the depth first ordering */
411 computeDFOrdering (ebbs[0], &count);
413 /* mark blocks with no paths to them */
414 markNoPath (ebbs, saveCount);
416 /* with the depth first info in place */
417 /* add the predecessors for the blocks */
418 eBBPredecessors (ebbs, saveCount);
420 /* compute the dominance graph */
421 computeDominance (ebbs, saveCount);
423 /* sort it by dfnumber */
424 qsort (ebbs, saveCount, sizeof (eBBlock *), dfNumCompare);
428 /*-----------------------------------------------------------------*/
429 /* returnAtEnd - returns 1 if Basic Block has a return at the end */
431 /*-----------------------------------------------------------------*/
432 int returnAtEnd (eBBlock *ebp)
435 This basic block ends in a return statment
437 if (ebp->ech && ebp->ech->op == RETURN) return 1;
440 This basic block has only one successor and that
441 successor has only one return statement
443 if (elementsInSet(ebp->succList) == 1) {
444 eBBlock *succ = setFirstItem(ebp->succList);
445 /* could happen for dummy blocks */
446 if (!succ->sch || !succ->ech) return 0;
448 /* first iCode is a return */
449 if (succ->sch->op == RETURN) return 2;
451 /* or first iCode is a label & the next &
452 last icode is a return */
453 if (succ->sch->op == LABEL && succ->sch->next == succ->ech &&
454 succ->ech->op == RETURN ) return 2;