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// SPDX-License-Identifier: MIT
//
// Various utilities for flowgraphs.
//
// Copyright (c) 2017 Luc Van Oostenryck.
//
#include "flowgraph.h"
#include "linearize.h"
#include "flow.h" // for bb_generation
#include <assert.h>
#include <stdio.h>
#include <stdlib.h>
struct cfg_info {
struct basic_block_list *list;
unsigned long gen;
unsigned int nr;
};
static void label_postorder(struct basic_block *bb, struct cfg_info *info)
{
struct basic_block *child;
if (bb->generation == info->gen)
return;
bb->generation = info->gen;
FOR_EACH_PTR_REVERSE(bb->children, child) {
label_postorder(child, info);
} END_FOR_EACH_PTR_REVERSE(child);
bb->postorder_nr = info->nr++;
add_bb(&info->list, bb);
}
static void reverse_bbs(struct basic_block_list **dst, struct basic_block_list *src)
{
struct basic_block *bb;
FOR_EACH_PTR_REVERSE(src, bb) {
add_bb(dst, bb);
} END_FOR_EACH_PTR_REVERSE(bb);
}
static void debug_postorder(struct entrypoint *ep)
{
struct basic_block *bb;
printf("%s's reverse postorder:\n", show_ident(ep->name->ident));
FOR_EACH_PTR(ep->bbs, bb) {
printf("\t.L%u: %u\n", bb->nr, bb->postorder_nr);
} END_FOR_EACH_PTR(bb);
}
//
// cfg_postorder - Set the BB's reverse postorder links
//
// Do a postorder DFS walk and set the links
// (which will do the reverse part).
//
int cfg_postorder(struct entrypoint *ep)
{
struct cfg_info info = {
.gen = ++bb_generation,
};
label_postorder(ep->entry->bb, &info);
// OK, now info.list contains the node in postorder
// Reuse ep->bbs for the reverse postorder.
free_ptr_list(&ep->bbs);
ep->bbs = NULL;
reverse_bbs(&ep->bbs, info.list);
free_ptr_list(&info.list);
if (dbg_postorder)
debug_postorder(ep);
return info.nr;
}
//
// Calculate the dominance tree following:
// "A simple, fast dominance algorithm"
// by K. D. Cooper, T. J. Harvey, and K. Kennedy.
// cfr. http://www.cs.rice.edu/∼keith/EMBED/dom.pdf
//
static struct basic_block *intersect_dom(struct basic_block *doms[],
struct basic_block *b1, struct basic_block *b2)
{
int f1 = b1->postorder_nr, f2 = b2->postorder_nr;
while (f1 != f2) {
while (f1 < f2) {
b1 = doms[f1];
f1 = b1->postorder_nr;
}
while (f2 < f1) {
b2 = doms[f2];
f2 = b2->postorder_nr;
}
}
return b1;
}
static void debug_domtree(struct entrypoint *ep)
{
struct basic_block *bb = ep->entry->bb;
printf("%s's idoms:\n", show_ident(ep->name->ident));
FOR_EACH_PTR(ep->bbs, bb) {
if (bb == ep->entry->bb)
continue; // entry node has no idom
printf("\t%s <- %s\n", show_label(bb), show_label(bb->idom));
} END_FOR_EACH_PTR(bb);
}
void domtree_build(struct entrypoint *ep)
{
struct basic_block *entry = ep->entry->bb;
struct basic_block **doms;
struct basic_block *bb;
unsigned int size;
int max_level = 0;
int changed;
// First calculate the (reverse) postorder.
// This will give use us:
// - the links to do a reverse postorder traversal
// - the order number for each block
size = cfg_postorder(ep);
// initialize the dominators array
doms = calloc(size, sizeof(*doms));
assert(entry->postorder_nr == size-1);
doms[size-1] = entry;
do {
struct basic_block *b;
changed = 0;
FOR_EACH_PTR(ep->bbs, b) {
struct basic_block *p;
int bnr = b->postorder_nr;
struct basic_block *new_idom = NULL;
if (b == entry)
continue; // ignore entry node
FOR_EACH_PTR(b->parents, p) {
unsigned int pnr = p->postorder_nr;
if (!doms[pnr])
continue;
if (!new_idom) {
new_idom = p;
continue;
}
new_idom = intersect_dom(doms, p, new_idom);
} END_FOR_EACH_PTR(p);
assert(new_idom);
if (doms[bnr] != new_idom) {
doms[bnr] = new_idom;
changed = 1;
}
} END_FOR_EACH_PTR(b);
} while (changed);
FOR_EACH_PTR(ep->bbs, bb) {
free_ptr_list(&bb->doms);
} END_FOR_EACH_PTR(bb);
// set the idom links
FOR_EACH_PTR(ep->bbs, bb) {
struct basic_block *idom = doms[bb->postorder_nr];
if (bb == entry)
continue; // ignore entry node
bb->idom = idom;
add_bb(&idom->doms, bb);
} END_FOR_EACH_PTR(bb);
entry->idom = NULL;
// set the dominance levels
FOR_EACH_PTR(ep->bbs, bb) {
struct basic_block *idom = bb->idom;
int level = idom ? idom->dom_level + 1 : 0;
bb->dom_level = level;
if (max_level < level)
max_level = level;
} END_FOR_EACH_PTR(bb);
ep->dom_levels = max_level + 1;
free(doms);
if (dbg_domtree)
debug_domtree(ep);
}
// dt_dominates - does BB a dominates BB b?
bool domtree_dominates(struct basic_block *a, struct basic_block *b)
{
if (a == b) // dominance is reflexive
return true;
if (a == b->idom)
return true;
if (b == a->idom)
return false;
// can't dominate if deeper in the DT
if (a->dom_level >= b->dom_level)
return false;
// FIXME: can be faster if we have the DFS in-out numbers
// walk up the dominator tree
for (b = b->idom; b; b = b->idom) {
if (b == a)
return true;
}
return false;
}
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