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 */
136 if (i && ebbs[i-1]->ech && ebbs[i-1]->ech->op==IFX) {
137 ebbs[i]->isConditionalExitFrom=ebbs[i-1];
140 } /* no instructions in the block */
141 /* could happen for dummy blocks */
143 addSuccessor (ebbs[i], ebbs[i + 1]);
146 /* go thru all the instructions: if we find a */
147 /* goto or ifx or a return then we have a succ */
148 if ((ic = ebbs[i]->ech))
152 /* special case for jumptable */
153 if (ic->op == JUMPTABLE)
156 for (lbl = setFirstItem (IC_JTLABELS (ic)); lbl;
157 lbl = setNextItem (IC_JTLABELS (ic)))
158 addSuccessor (ebbs[i],
159 eBBWithEntryLabel (ebbs, lbl, count));
165 /* depending on the instruction operator */
168 case GOTO: /* goto has edge to label */
169 succ = eBBWithEntryLabel (ebbs, ic->label, count);
172 case IFX: /* conditional jump */
173 /* if true label is present */
175 succ = eBBWithEntryLabel (ebbs, IC_TRUE (ic), count);
177 succ = eBBWithEntryLabel (ebbs, IC_FALSE (ic), count);
180 case RETURN: /* block with return */
181 succ = eBBWithEntryLabel (ebbs, returnLabel, count);
185 /* if there is a successor add to the list */
186 /* if it is not already present in the list */
188 addSuccessor (ebbs[i], succ);
194 /*-----------------------------------------------------------------*/
195 /* computeDominance - computes the dominance graph */
196 /* for algorithm look at Dragon book section 10.10, algo 10.16 */
197 /*-----------------------------------------------------------------*/
199 computeDominance (eBBlock ** ebbs, int count)
203 /* now do the initialisation */
204 /* D(n0) := { n0 } */
206 bitVectSetBit (ebbs[0]->domVect = newBitVect (count), ebbs[0]->bbnum);
209 /* for n in N - { n0 } do D(n) = N */
210 for (i = 1; i < count; i++)
212 ebbs[i]->domVect = newBitVect (count);
213 for (j = 0; j < count; j++)
216 bitVectSetBit (ebbs[i]->domVect, ebbs[j]->bbnum);
220 /* end of initialisation */
222 /* while changes to any D(n) occur do */
223 /* for n in N - { n0 } do */
224 /* D(n) := { n } U (intersection of D( all predecessors of n)) */
230 for (i = 1; i < count; i++)
237 /* get the intersection of the dominance of all predecessors */
238 for (pred = setFirstItem (ebbs[i]->predList),
239 cDomVect = (pred ? bitVectCopy (pred->domVect) : NULL);
241 pred = setNextItem (ebbs[i]->predList))
243 cDomVect = bitVectIntersect (cDomVect, pred->domVect);
246 cDomVect = newBitVect (count);
247 /* this node to the list */
248 cDomVect = bitVectSetBit (cDomVect, ebbs[i]->bbnum);
251 if (!bitVectEqual (cDomVect, ebbs[i]->domVect))
253 ebbs[i]->domVect = cDomVect;
258 /* if no change then exit */
264 /*-----------------------------------------------------------------*/
265 /* immedDom - returns the immediate dominator of a block */
266 /*-----------------------------------------------------------------*/
268 immedDom (eBBlock ** ebbs, eBBlock * ebp)
270 /* first delete self from the list */
271 set *iset = domSetFromVect (ebbs, ebp->domVect);
273 eBBlock *idom = NULL;
275 deleteSetItem (&iset, ebp);
276 /* then just return the one with the greatest */
277 /* depthfirst number, this will be the immed dominator */
278 if ((loop = setFirstItem (iset)))
280 for (; loop; loop = setNextItem (iset))
281 if (loop->dfnum > idom->dfnum)
284 setToNull ((void **) &iset);
289 /*-----------------------------------------------------------------*/
290 /* DFOrdering - is visited then nothing else call DFOrdering this */
291 /*-----------------------------------------------------------------*/
292 DEFSETFUNC (DFOrdering)
294 eBBlock *ebbp = item;
295 V_ARG (int *, count);
300 computeDFOrdering (ebbp, count); /* depthfirst */
305 /*-----------------------------------------------------------------*/
306 /* computeDFOrdering - computes the depth first ordering of the */
308 /*-----------------------------------------------------------------*/
310 computeDFOrdering (eBBlock * ebbp, int *count)
314 /* for each successor that is not visited */
315 applyToSet (ebbp->succList, DFOrdering, count);
317 /* set the depth first number */
318 ebbp->dfnum = *count;
322 /*-----------------------------------------------------------------*/
323 /* disconBBlock - removes all control flow links for a block */
324 /*-----------------------------------------------------------------*/
326 disconBBlock (eBBlock * ebp, eBBlock ** ebbs, int count)
328 /* mark this block as noPath & recompute control flow */
330 computeControlFlow (ebbs, count, TRUE);
333 /*-----------------------------------------------------------------*/
334 /* markNoPath - marks those blocks which cannot be reached from top */
335 /*-----------------------------------------------------------------*/
337 markNoPath (eBBlock ** ebbs, int count)
342 /* for all blocks if the visited flag is not set : then there */
343 /* is no path from _entry to this block push them down in the */
344 /* depth first order */
345 for (i = 0; i < count; i++)
346 if (!ebbs[i]->visited)
349 /*-----------------------------------------------------------------*/
350 /* dfNumCompare - used by qsort to sort by dfNumber */
351 /*-----------------------------------------------------------------*/
353 dfNumCompare (const void *a, const void *b)
355 const eBBlock *const *i = a;
356 const eBBlock *const *j = b;
358 if ((*i)->dfnum > (*j)->dfnum)
361 if ((*i)->dfnum < (*j)->dfnum)
367 /*-----------------------------------------------------------------*/
368 /* bbNumCompare - used by qsort to sort by bbNumber */
369 /*-----------------------------------------------------------------*/
371 bbNumCompare (const void *a, const void *b)
373 const eBBlock *const *i = a;
374 const eBBlock *const *j = b;
376 if ((*i)->bbnum > (*j)->bbnum)
379 if ((*i)->bbnum < (*j)->bbnum)
386 /*-----------------------------------------------------------------*/
387 /* computeControlFlow - does the control flow computation */
388 /*-----------------------------------------------------------------*/
390 computeControlFlow (eBBlock ** ebbs, int count, int reSort)
392 int saveCount = count;
395 /* initialise some things */
397 for (i = 0; i < count; i++)
399 setToNull ((void **) &ebbs[i]->predList);
400 setToNull ((void **) &ebbs[i]->domVect);
401 setToNull ((void **) &ebbs[i]->succList);
402 setToNull ((void **) &ebbs[i]->succVect);
403 ebbs[i]->visited = 0;
408 /* sort it back by block number */
409 qsort (ebbs, saveCount, sizeof (eBBlock *), bbNumCompare);
411 setToNull ((void **) &graphEdges);
412 /* this will put in the */
413 /* successor information for each blk */
414 eBBSuccessors (ebbs, count);
416 /* compute the depth first ordering */
417 computeDFOrdering (ebbs[0], &count);
419 /* mark blocks with no paths to them */
420 markNoPath (ebbs, saveCount);
422 /* with the depth first info in place */
423 /* add the predecessors for the blocks */
424 eBBPredecessors (ebbs, saveCount);
426 /* compute the dominance graph */
427 computeDominance (ebbs, saveCount);
429 /* sort it by dfnumber */
430 qsort (ebbs, saveCount, sizeof (eBBlock *), dfNumCompare);
434 /*-----------------------------------------------------------------*/
435 /* returnAtEnd - returns 1 if Basic Block has a return at the end */
437 /*-----------------------------------------------------------------*/
438 int returnAtEnd (eBBlock *ebp)
441 This basic block ends in a return statment
443 if (ebp->ech && ebp->ech->op == RETURN) return 1;
446 This basic block has only one successor and that
447 successor has only one return statement
449 if (elementsInSet(ebp->succList) == 1) {
450 eBBlock *succ = setFirstItem(ebp->succList);
451 /* could happen for dummy blocks */
452 if (!succ->sch || !succ->ech) return 0;
454 /* first iCode is a return */
455 if (succ->sch->op == RETURN) return 2;
457 /* or first iCode is a label & the next &
458 last icode is a return */
459 if (succ->sch->op == LABEL && succ->sch->next == succ->ech &&
460 succ->ech->op == RETURN ) return 2;