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ir_cfg.c
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ir_cfg.c
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/*
* IR - Lightweight JIT Compilation Framework
* (CFG - Control Flow Graph)
* Copyright (C) 2022 Zend by Perforce.
* Authors: Dmitry Stogov <[email protected]>
*/
#include "ir.h"
#include "ir_private.h"
IR_ALWAYS_INLINE void _ir_add_successors(const ir_ctx *ctx, ir_ref ref, ir_worklist *worklist)
{
ir_use_list *use_list = &ctx->use_lists[ref];
ir_ref *p, use, n = use_list->count;
if (n < 2) {
if (n == 1) {
use = ctx->use_edges[use_list->refs];
IR_ASSERT(ir_op_flags[ctx->ir_base[use].op] & IR_OP_FLAG_CONTROL);
ir_worklist_push(worklist, use);
}
} else {
p = &ctx->use_edges[use_list->refs];
if (n == 2) {
use = *p;
IR_ASSERT(ir_op_flags[ctx->ir_base[use].op] & IR_OP_FLAG_CONTROL);
ir_worklist_push(worklist, use);
use = *(p + 1);
IR_ASSERT(ir_op_flags[ctx->ir_base[use].op] & IR_OP_FLAG_CONTROL);
ir_worklist_push(worklist, use);
} else {
for (; n > 0; p++, n--) {
use = *p;
IR_ASSERT(ir_op_flags[ctx->ir_base[use].op] & IR_OP_FLAG_CONTROL);
ir_worklist_push(worklist, use);
}
}
}
}
IR_ALWAYS_INLINE void _ir_add_predecessors(const ir_insn *insn, ir_worklist *worklist)
{
ir_ref n, ref;
const ir_ref *p;
if (insn->op == IR_MERGE || insn->op == IR_LOOP_BEGIN) {
n = insn->inputs_count;
for (p = insn->ops + 1; n > 0; p++, n--) {
ref = *p;
IR_ASSERT(ref);
ir_worklist_push(worklist, ref);
}
} else if (insn->op != IR_START) {
if (EXPECTED(insn->op1)) {
ir_worklist_push(worklist, insn->op1);
}
}
}
int ir_build_cfg(ir_ctx *ctx)
{
ir_ref n, *p, ref, start, end, next;
uint32_t b;
ir_insn *insn;
ir_worklist worklist;
uint32_t bb_init_falgs;
uint32_t count, bb_count = 0;
uint32_t edges_count = 0;
ir_block *blocks, *bb;
uint32_t *_blocks, *edges;
ir_use_list *use_list;
uint32_t len = ir_bitset_len(ctx->insns_count);
ir_bitset bb_starts = ir_mem_calloc(len * 2, IR_BITSET_BITS / 8);
ir_bitset bb_leaks = bb_starts + len;
_blocks = ir_mem_calloc(ctx->insns_count, sizeof(uint32_t));
ir_worklist_init(&worklist, ctx->insns_count);
/* First try to perform backward DFS search starting from "stop" nodes */
/* Add all "stop" nodes */
ref = ctx->ir_base[1].op1;
while (ref) {
ir_worklist_push(&worklist, ref);
ref = ctx->ir_base[ref].op3;
}
while (ir_worklist_len(&worklist)) {
ref = ir_worklist_pop(&worklist);
insn = &ctx->ir_base[ref];
if (insn->op == IR_NOP) {
continue;
}
IR_ASSERT(IR_IS_BB_END(insn->op));
/* Remember BB end */
end = ref;
/* Some successors of IF and SWITCH nodes may be inaccessible by backward DFS */
use_list = &ctx->use_lists[end];
n = use_list->count;
if (n > 1 || (n == 1 && (ir_op_flags[insn->op] & IR_OP_FLAG_TERMINATOR) != 0)) {
for (p = &ctx->use_edges[use_list->refs]; n > 0; p++, n--) {
/* Remember possible inaccessible successors */
ir_bitset_incl(bb_leaks, *p);
}
}
/* Skip control nodes untill BB start */
ref = insn->op1;
while (1) {
insn = &ctx->ir_base[ref];
if (IR_IS_BB_START(insn->op)) {
break;
}
ref = insn->op1; // follow connected control blocks untill BB start
}
/* Mark BB Start */
bb_count++;
_blocks[ref] = end;
ir_bitset_incl(bb_starts, ref);
/* Add predecessors */
_ir_add_predecessors(insn, &worklist);
}
/* Backward DFS way miss some branches ending by infinite loops. */
/* Try forward DFS. (in most cases all nodes are already proceed). */
/* START node may be inaccessible from "stop" nodes */
ir_bitset_incl(bb_leaks, 1);
/* Add not processed START and successor of IF and SWITCH */
IR_BITSET_FOREACH_DIFFERENCE(bb_leaks, bb_starts, len, start) {
ir_worklist_push(&worklist, start);
} IR_BITSET_FOREACH_END();
if (ir_worklist_len(&worklist)) {
ir_bitset_union(worklist.visited, bb_starts, len);
do {
ref = ir_worklist_pop(&worklist);
insn = &ctx->ir_base[ref];
if (insn->op == IR_NOP) {
continue;
}
IR_ASSERT(IR_IS_BB_START(insn->op));
/* Remember BB start */
start = ref;
/* Skip control nodes untill BB end */
while (1) {
use_list = &ctx->use_lists[ref];
n = use_list->count;
next = IR_UNUSED;
for (p = &ctx->use_edges[use_list->refs]; n > 0; p++, n--) {
next = *p;
insn = &ctx->ir_base[next];
if ((ir_op_flags[insn->op] & IR_OP_FLAG_CONTROL) && insn->op1 == ref) {
break;
}
}
IR_ASSERT(next != IR_UNUSED);
ref = next;
if (IR_IS_BB_END(insn->op)) {
break;
}
}
/* Mark BB Start */
bb_count++;
_blocks[start] = ref;
ir_bitset_incl(bb_starts, start);
/* Add successors */
_ir_add_successors(ctx, ref, &worklist);
} while (ir_worklist_len(&worklist));
}
IR_ASSERT(bb_count > 0);
/* Create array of basic blocks and count successor/predecessors edges for each BB */
blocks = ir_mem_malloc((bb_count + 1) * sizeof(ir_block));
b = 1;
bb = blocks + 1;
count = 0;
/* SCCP already removed UNREACHABKE blocks, otherwise all blocks are marked as UNREACHABLE first */
bb_init_falgs = (ctx->flags2 & IR_CFG_REACHABLE) ? 0 : IR_BB_UNREACHABLE;
IR_BITSET_FOREACH(bb_starts, len, start) {
insn = &ctx->ir_base[start];
if (insn->op == IR_NOP) {
_blocks[start] = 0;
continue;
}
end = _blocks[start];
_blocks[start] = b;
_blocks[end] = b;
IR_ASSERT(IR_IS_BB_START(insn->op));
IR_ASSERT(end > start);
bb->start = start;
bb->end = end;
bb->successors = count;
count += ctx->use_lists[end].count;
bb->successors_count = 0;
bb->predecessors = count;
bb->dom_parent = 0;
bb->dom_depth = 0;
bb->dom_child = 0;
bb->dom_next_child = 0;
bb->loop_header = 0;
bb->loop_depth = 0;
if (insn->op == IR_START) {
bb->flags = IR_BB_START;
bb->predecessors_count = 0;
} else {
bb->flags = bb_init_falgs;
if (insn->op == IR_MERGE || insn->op == IR_LOOP_BEGIN) {
n = insn->inputs_count;
bb->predecessors_count = n;
edges_count += n;
count += n;
} else if (EXPECTED(insn->op1)) {
if (insn->op == IR_ENTRY) {
bb->flags |= IR_BB_ENTRY;
ctx->entries_count++;
}
bb->predecessors_count = 1;
edges_count++;
count++;
} else {
IR_ASSERT(insn->op == IR_BEGIN); /* start of unreachable block */
bb->predecessors_count = 0;
}
}
b++;
bb++;
} IR_BITSET_FOREACH_END();
bb_count = b - 1;
IR_ASSERT(count == edges_count * 2);
ir_mem_free(bb_starts);
/* Create an array of successor/predecessors control edges */
edges = ir_mem_malloc(edges_count * 2 * sizeof(uint32_t));
bb = blocks + 1;
for (b = 1; b <= bb_count; b++, bb++) {
insn = &ctx->ir_base[bb->start];
if (bb->predecessors_count > 1) {
uint32_t *q = edges + bb->predecessors;
n = insn->inputs_count;
for (p = insn->ops + 1; n > 0; p++, q++, n--) {
ref = *p;
IR_ASSERT(ref);
ir_ref pred_b = _blocks[ref];
ir_block *pred_bb = &blocks[pred_b];
IR_ASSERT(pred_b > 0);
*q = pred_b;
edges[pred_bb->successors + pred_bb->successors_count++] = b;
}
} else if (bb->predecessors_count == 1) {
ref = insn->op1;
IR_ASSERT(ref);
IR_ASSERT(IR_OPND_KIND(ir_op_flags[insn->op], 1) == IR_OPND_CONTROL);
ir_ref pred_b = _blocks[ref];
ir_block *pred_bb = &blocks[pred_b];
edges[bb->predecessors] = pred_b;
edges[pred_bb->successors + pred_bb->successors_count++] = b;
}
}
ctx->cfg_blocks_count = bb_count;
ctx->cfg_edges_count = edges_count * 2;
ctx->cfg_blocks = blocks;
ctx->cfg_edges = edges;
ctx->cfg_map = _blocks;
if (!(ctx->flags2 & IR_CFG_REACHABLE)) {
uint32_t reachable_count = 0;
/* Mark reachable blocks */
ir_worklist_clear(&worklist);
ir_worklist_push(&worklist, 1);
while (ir_worklist_len(&worklist) != 0) {
uint32_t *p;
reachable_count++;
b = ir_worklist_pop(&worklist);
bb = &blocks[b];
bb->flags &= ~IR_BB_UNREACHABLE;
n = bb->successors_count;
if (n > 1) {
for (p = edges + bb->successors; n > 0; p++, n--) {
ir_worklist_push(&worklist, *p);
}
} else if (n == 1) {
ir_worklist_push(&worklist, edges[bb->successors]);
}
}
if (reachable_count != ctx->cfg_blocks_count) {
ir_remove_unreachable_blocks(ctx);
}
}
ir_worklist_free(&worklist);
return 1;
}
static void ir_remove_predecessor(ir_ctx *ctx, ir_block *bb, uint32_t from)
{
uint32_t i, *p, *q, n = 0;
p = q = &ctx->cfg_edges[bb->predecessors];
for (i = 0; i < bb->predecessors_count; i++, p++) {
if (*p != from) {
if (p != q) {
*q = *p;
}
q++;
n++;
}
}
IR_ASSERT(n != bb->predecessors_count);
bb->predecessors_count = n;
}
static void ir_remove_merge_input(ir_ctx *ctx, ir_ref merge, ir_ref from)
{
ir_ref i, j, n, k, *p, use;
ir_insn *use_insn;
ir_use_list *use_list;
ir_bitset life_inputs;
ir_insn *insn = &ctx->ir_base[merge];
IR_ASSERT(insn->op == IR_MERGE || insn->op == IR_LOOP_BEGIN);
n = insn->inputs_count;
i = 1;
life_inputs = ir_bitset_malloc(n + 1);
for (j = 1; j <= n; j++) {
ir_ref input = ir_insn_op(insn, j);
if (input != from) {
if (i != j) {
ir_insn_set_op(insn, i, input);
}
ir_bitset_incl(life_inputs, j);
i++;
}
}
i--;
if (i == 1) {
insn->op = IR_BEGIN;
insn->inputs_count = 1;
use_list = &ctx->use_lists[merge];
if (use_list->count > 1) {
for (k = 0, p = &ctx->use_edges[use_list->refs]; k < use_list->count; k++, p++) {
use = *p;
use_insn = &ctx->ir_base[use];
if (use_insn->op == IR_PHI) {
/* Convert PHI to COPY */
i = 2;
for (j = 2; j <= n; j++) {
ir_ref input = ir_insn_op(use_insn, j);
if (ir_bitset_in(life_inputs, j - 1)) {
use_insn->op1 = ir_insn_op(use_insn, j);
} else if (input > 0) {
ir_use_list_remove_all(ctx, input, use);
}
}
use_insn->op = IR_COPY;
use_insn->op2 = IR_UNUSED;
use_insn->op3 = IR_UNUSED;
ir_use_list_remove_all(ctx, merge, use);
}
}
}
} else {
insn->inputs_count = i;
n++;
use_list = &ctx->use_lists[merge];
if (use_list->count > 1) {
for (k = 0, p = &ctx->use_edges[use_list->refs]; k < use_list->count; k++, p++) {
use = *p;
use_insn = &ctx->ir_base[use];
if (use_insn->op == IR_PHI) {
i = 2;
for (j = 2; j <= n; j++) {
ir_ref input = ir_insn_op(use_insn, j);
if (ir_bitset_in(life_inputs, j - 1)) {
IR_ASSERT(input);
if (i != j) {
ir_insn_set_op(use_insn, i, input);
}
i++;
} else if (input > 0) {
ir_use_list_remove_all(ctx, input, use);
}
}
}
}
}
}
ir_mem_free(life_inputs);
ir_use_list_remove_all(ctx, from, merge);
}
/* CFG constructed after SCCP pass doesn't have unreachable BBs, otherwise they should be removed */
int ir_remove_unreachable_blocks(ir_ctx *ctx)
{
uint32_t b, *p, i;
uint32_t unreachable_count = 0;
uint32_t bb_count = ctx->cfg_blocks_count;
ir_block *bb = ctx->cfg_blocks + 1;
for (b = 1; b <= bb_count; b++, bb++) {
if (bb->flags & IR_BB_UNREACHABLE) {
#if 0
do {if (!unreachable_count) ir_dump_cfg(ctx, stderr);} while(0);
#endif
if (bb->successors_count) {
for (i = 0, p = &ctx->cfg_edges[bb->successors]; i < bb->successors_count; i++, p++) {
ir_block *succ_bb = &ctx->cfg_blocks[*p];
if (!(succ_bb->flags & IR_BB_UNREACHABLE)) {
ir_remove_predecessor(ctx, succ_bb, b);
ir_remove_merge_input(ctx, succ_bb->start, bb->end);
}
}
} else {
ir_ref prev, ref = bb->end;
ir_insn *insn = &ctx->ir_base[ref];
IR_ASSERT(ir_op_flags[insn->op] & IR_OP_FLAG_TERMINATOR);
/* remove from terminators list */
prev = ctx->ir_base[1].op1;
if (prev == ref) {
ctx->ir_base[1].op1 = insn->op3;
} else {
while (prev) {
if (ctx->ir_base[prev].op3 == ref) {
ctx->ir_base[prev].op3 = insn->op3;
break;
}
prev = ctx->ir_base[prev].op3;
}
}
}
ctx->cfg_map[bb->start] = 0;
ctx->cfg_map[bb->end] = 0;
unreachable_count++;
}
}
if (unreachable_count) {
ir_block *dst_bb;
uint32_t n = 1;
uint32_t *edges;
dst_bb = bb = ctx->cfg_blocks + 1;
for (b = 1; b <= bb_count; b++, bb++) {
if (!(bb->flags & IR_BB_UNREACHABLE)) {
if (dst_bb != bb) {
memcpy(dst_bb, bb, sizeof(ir_block));
ctx->cfg_map[dst_bb->start] = n;
ctx->cfg_map[dst_bb->end] = n;
}
dst_bb->successors_count = 0;
dst_bb++;
n++;
}
}
ctx->cfg_blocks_count = bb_count = n - 1;
/* Rebuild successor/predecessors control edges */
edges = ctx->cfg_edges;
bb = ctx->cfg_blocks + 1;
for (b = 1; b <= bb_count; b++, bb++) {
ir_insn *insn = &ctx->ir_base[bb->start];
ir_ref *p, ref;
n = bb->predecessors_count;
if (n > 1) {
uint32_t *q = edges + bb->predecessors;
IR_ASSERT(n == insn->inputs_count);
for (p = insn->ops + 1; n > 0; p++, q++, n--) {
ref = *p;
IR_ASSERT(ref);
ir_ref pred_b = ctx->cfg_map[ref];
ir_block *pred_bb = &ctx->cfg_blocks[pred_b];
*q = pred_b;
edges[pred_bb->successors + pred_bb->successors_count++] = b;
}
} else if (n == 1) {
ref = insn->op1;
IR_ASSERT(ref);
IR_ASSERT(IR_OPND_KIND(ir_op_flags[insn->op], 1) == IR_OPND_CONTROL);
ir_ref pred_b = ctx->cfg_map[ref];
ir_block *pred_bb = &ctx->cfg_blocks[pred_b];
edges[bb->predecessors] = pred_b;
edges[pred_bb->successors + pred_bb->successors_count++] = b;
}
}
}
return 1;
}
#if 0
static void compute_postnum(const ir_ctx *ctx, uint32_t *cur, uint32_t b)
{
uint32_t i, *p;
ir_block *bb = &ctx->cfg_blocks[b];
if (bb->postnum != 0) {
return;
}
if (bb->successors_count) {
bb->postnum = -1; /* Marker for "currently visiting" */
p = ctx->cfg_edges + bb->successors;
i = bb->successors_count;
do {
compute_postnum(ctx, cur, *p);
p++;
} while (--i);
}
bb->postnum = (*cur)++;
}
/* Computes dominator tree using algorithm from "A Simple, Fast Dominance Algorithm" by
* Cooper, Harvey and Kennedy. */
int ir_build_dominators_tree(ir_ctx *ctx)
{
uint32_t blocks_count, b, postnum;
ir_block *blocks, *bb;
uint32_t *edges;
bool changed;
ctx->flags2 &= ~IR_NO_LOOPS;
postnum = 1;
compute_postnum(ctx, &postnum, 1);
/* Find immediate dominators */
blocks = ctx->cfg_blocks;
edges = ctx->cfg_edges;
blocks_count = ctx->cfg_blocks_count;
blocks[1].idom = 1;
do {
changed = 0;
/* Iterating in Reverse Post Order */
for (b = 2, bb = &blocks[2]; b <= blocks_count; b++, bb++) {
IR_ASSERT(!(bb->flags & IR_BB_UNREACHABLE));
if (bb->predecessors_count == 1) {
uint32_t pred_b = edges[bb->predecessors];
if (blocks[pred_b].idom <= 0) {
//IR_ASSERT("Wrong blocks order: BB is before its single predecessor");
} else if (bb->idom != pred_b) {
bb->idom = pred_b;
changed = 1;
}
} else if (bb->predecessors_count) {
uint32_t idom = 0;
uint32_t k = bb->predecessors_count;
uint32_t *p = edges + bb->predecessors;
do {
uint32_t pred_b = *p;
ir_block *pred_bb = &blocks[pred_b];
ir_block *idom_bb;
if (pred_bb->idom > 0) {
idom = pred_b;
idom_bb = &blocks[idom];
while (--k > 0) {
pred_b = *(++p);
pred_bb = &blocks[pred_b];
if (pred_bb->idom > 0) {
while (idom != pred_b) {
while (pred_bb->postnum < idom_bb->postnum) {
pred_b = pred_bb->idom;
pred_bb = &blocks[pred_b];
}
while (idom_bb->postnum < pred_bb->postnum) {
idom = idom_bb->idom;
idom_bb = &blocks[idom];
}
}
}
}
if (bb->idom != idom) {
bb->idom = idom;
changed = 1;
}
break;
}
p++;
} while (--k > 0);
}
}
} while (changed);
blocks[1].idom = 0;
blocks[1].dom_depth = 0;
/* Construct dominators tree */
for (b = 2, bb = &blocks[2]; b <= blocks_count; b++, bb++) {
IR_ASSERT(!(bb->flags & IR_BB_UNREACHABLE));
if (bb->idom > 0) {
ir_block *idom_bb = &blocks[bb->idom];
bb->dom_depth = idom_bb->dom_depth + 1;
/* Sort by block number to traverse children in pre-order */
if (idom_bb->dom_child == 0) {
idom_bb->dom_child = b;
} else if (b < idom_bb->dom_child) {
bb->dom_next_child = idom_bb->dom_child;
idom_bb->dom_child = b;
} else {
int child = idom_bb->dom_child;
ir_block *child_bb = &blocks[child];
while (child_bb->dom_next_child > 0 && b > child_bb->dom_next_child) {
child = child_bb->dom_next_child;
child_bb = &blocks[child];
}
bb->dom_next_child = child_bb->dom_next_child;
child_bb->dom_next_child = b;
}
}
}
return 1;
}
#else
/* A single pass modification of "A Simple, Fast Dominance Algorithm" by
* Cooper, Harvey and Kennedy, that relays on IR block ordering.
* It may fallback to the general slow fixed-point algorithm. */
static int ir_build_dominators_tree_iterative(ir_ctx *ctx);
int ir_build_dominators_tree(ir_ctx *ctx)
{
uint32_t blocks_count, b;
ir_block *blocks, *bb;
uint32_t *edges;
ir_list worklist;
ir_list_init(&worklist, ctx->cfg_blocks_count / 2);
ctx->flags2 |= IR_NO_LOOPS;
/* Find immediate dominators */
blocks = ctx->cfg_blocks;
edges = ctx->cfg_edges;
blocks_count = ctx->cfg_blocks_count;
blocks[1].idom = 1;
blocks[1].dom_depth = 0;
/* Iterating in Reverse Post Order */
for (b = 2, bb = &blocks[2]; b <= blocks_count; b++, bb++) {
IR_ASSERT(!(bb->flags & IR_BB_UNREACHABLE));
IR_ASSERT(bb->predecessors_count > 0);
uint32_t k = bb->predecessors_count;
uint32_t *p = edges + bb->predecessors;
uint32_t idom = *p;
ir_block *idom_bb;
if (UNEXPECTED(idom >= b)) {
/* In rare cases, LOOP_BEGIN.op1 may be a back-edge. Skip back-edges. */
ctx->flags2 &= ~IR_NO_LOOPS;
IR_ASSERT(k > 1 && "Wrong blocks order: BB is before its single predecessor");
ir_list_push(&worklist, idom);
while (1) {
k--;
p++;
idom = *p;
if (idom < b) {
break;
}
IR_ASSERT(k > 0);
ir_list_push(&worklist, idom);
}
}
IR_ASSERT(blocks[idom].idom > 0);
IR_ASSERT(k != 0);
while (--k > 0) {
uint32_t pred_b = *(++p);
if (pred_b < b) {
IR_ASSERT(blocks[pred_b].idom > 0);
while (idom != pred_b) {
while (pred_b > idom) {
pred_b = blocks[pred_b].idom;
}
while (idom > pred_b) {
idom = blocks[idom].idom;
}
}
} else {
ctx->flags2 &= ~IR_NO_LOOPS;
IR_ASSERT(bb->predecessors_count > 1);
ir_list_push(&worklist, pred_b);
}
}
bb->idom = idom;
idom_bb = &blocks[idom];
bb->dom_depth = idom_bb->dom_depth + 1;
/* Sort by block number to traverse children in pre-order */
if (idom_bb->dom_child == 0) {
idom_bb->dom_child = b;
} else if (b < idom_bb->dom_child) {
bb->dom_next_child = idom_bb->dom_child;
idom_bb->dom_child = b;
} else {
int child = idom_bb->dom_child;
ir_block *child_bb = &blocks[child];
while (child_bb->dom_next_child > 0 && b > child_bb->dom_next_child) {
child = child_bb->dom_next_child;
child_bb = &blocks[child];
}
bb->dom_next_child = child_bb->dom_next_child;
child_bb->dom_next_child = b;
}
}
blocks[1].idom = 0;
if (ir_list_len(&worklist) != 0) {
uint32_t dom_depth;
uint32_t succ_b;
bool complete = 1;
/* Check if all the back-edges lead to the loop headers */
do {
b = ir_list_pop(&worklist);
bb = &blocks[b];
succ_b = ctx->cfg_edges[bb->successors];
if (bb->successors_count != 1) {
/* LOOP_END/END may be linked with the following ENTRY by a fake edge */
IR_ASSERT(bb->successors_count == 2);
if (blocks[succ_b].flags & IR_BB_ENTRY) {
succ_b = ctx->cfg_edges[bb->successors + 1];
} else {
IR_ASSERT(blocks[ctx->cfg_edges[bb->successors + 1]].flags & IR_BB_ENTRY);
}
}
dom_depth = blocks[succ_b].dom_depth;;
while (bb->dom_depth > dom_depth) {
b = bb->dom_parent;
bb = &blocks[b];
}
if (UNEXPECTED(b != succ_b)) {
complete = 0;
break;
}
} while (ir_list_len(&worklist) != 0);
if (UNEXPECTED(!complete)) {
ir_list_free(&worklist);
return ir_build_dominators_tree_iterative(ctx);
}
}
ir_list_free(&worklist);
return 1;
}
static int ir_build_dominators_tree_iterative(ir_ctx *ctx)
{
bool changed;
uint32_t blocks_count, b;
ir_block *blocks, *bb;
uint32_t *edges;
/* Find immediate dominators */
blocks = ctx->cfg_blocks;
edges = ctx->cfg_edges;
blocks_count = ctx->cfg_blocks_count;
/* Clear the dominators tree, but keep already found dominators */
for (b = 0, bb = &blocks[0]; b <= blocks_count; b++, bb++) {
bb->dom_depth = 0;
bb->dom_child = 0;
bb->dom_next_child = 0;
}
/* Find immediate dominators by iterative fixed-point algorithm */
blocks[1].idom = 1;
do {
changed = 0;
for (b = 2, bb = &blocks[2]; b <= blocks_count; b++, bb++) {
IR_ASSERT(!(bb->flags & IR_BB_UNREACHABLE));
IR_ASSERT(bb->predecessors_count > 0);
uint32_t k = bb->predecessors_count;
uint32_t *p = edges + bb->predecessors;
uint32_t idom = *p;
if (blocks[idom].idom == 0) {
while (1) {
k--;
p++;
idom = *p;
if (blocks[idom].idom > 0) {
break;
}
IR_ASSERT(k > 0);
}
}
IR_ASSERT(k != 0);
while (--k > 0) {
uint32_t pred_b = *(++p);
if (blocks[pred_b].idom > 0) {
IR_ASSERT(blocks[pred_b].idom > 0);
while (idom != pred_b) {
while (pred_b > idom) {
pred_b = blocks[pred_b].idom;
}
while (idom > pred_b) {
idom = blocks[idom].idom;
}
}
}
}
if (bb->idom != idom) {
bb->idom = idom;
changed = 1;
}
}
} while (changed);
/* Build dominators tree */
blocks[1].idom = 0;
blocks[1].dom_depth = 0;
for (b = 2, bb = &blocks[2]; b <= blocks_count; b++, bb++) {
uint32_t idom = bb->idom;
ir_block *idom_bb = &blocks[idom];
bb->dom_depth = idom_bb->dom_depth + 1;
/* Sort by block number to traverse children in pre-order */
if (idom_bb->dom_child == 0) {
idom_bb->dom_child = b;
} else if (b < idom_bb->dom_child) {
bb->dom_next_child = idom_bb->dom_child;
idom_bb->dom_child = b;
} else {
int child = idom_bb->dom_child;
ir_block *child_bb = &blocks[child];
while (child_bb->dom_next_child > 0 && b > child_bb->dom_next_child) {
child = child_bb->dom_next_child;
child_bb = &blocks[child];
}
bb->dom_next_child = child_bb->dom_next_child;
child_bb->dom_next_child = b;
}
}
return 1;
}
#endif
static bool ir_dominates(const ir_block *blocks, uint32_t b1, uint32_t b2)
{
uint32_t b1_depth = blocks[b1].dom_depth;
const ir_block *bb2 = &blocks[b2];
while (bb2->dom_depth > b1_depth) {
b2 = bb2->dom_parent;
bb2 = &blocks[b2];
}
return b1 == b2;
}
int ir_find_loops(ir_ctx *ctx)
{
uint32_t i, j, n, count;
uint32_t *entry_times, *exit_times, *sorted_blocks, time = 1;
ir_block *blocks = ctx->cfg_blocks;
uint32_t *edges = ctx->cfg_edges;
ir_worklist work;
if (ctx->flags2 & IR_NO_LOOPS) {
return 1;
}
/* We don't materialize the DJ spanning tree explicitly, as we are only interested in ancestor
* queries. These are implemented by checking entry/exit times of the DFS search. */
ir_worklist_init(&work, ctx->cfg_blocks_count + 1);
entry_times = ir_mem_malloc((ctx->cfg_blocks_count + 1) * 3 * sizeof(uint32_t));
exit_times = entry_times + ctx->cfg_blocks_count + 1;
sorted_blocks = exit_times + ctx->cfg_blocks_count + 1;
memset(entry_times, 0, (ctx->cfg_blocks_count + 1) * sizeof(uint32_t));
ir_worklist_push(&work, 1);
while (ir_worklist_len(&work)) {
ir_block *bb;
int child;
next:
i = ir_worklist_peek(&work);
if (!entry_times[i]) {
entry_times[i] = time++;
}
/* Visit blocks immediately dominated by i. */
bb = &blocks[i];
for (child = bb->dom_child; child > 0; child = blocks[child].dom_next_child) {
if (ir_worklist_push(&work, child)) {
goto next;
}
}
/* Visit join edges. */
if (bb->successors_count) {
uint32_t *p = edges + bb->successors;
for (j = 0; j < bb->successors_count; j++,p++) {
uint32_t succ = *p;
if (blocks[succ].idom == i) {
continue;
} else if (ir_worklist_push(&work, succ)) {
goto next;
}
}
}
exit_times[i] = time++;
ir_worklist_pop(&work);
}
/* Sort blocks by level, which is the opposite order in which we want to process them */
sorted_blocks[1] = 1;
j = 1;
n = 2;
while (j != n) {
i = j;
j = n;
for (; i < j; i++) {
int child;
for (child = blocks[sorted_blocks[i]].dom_child; child > 0; child = blocks[child].dom_next_child) {
sorted_blocks[n++] = child;
}
}
}
count = n;
/* Identify loops. See Sreedhar et al, "Identifying Loops Using DJ Graphs". */
while (n > 1) {
i = sorted_blocks[--n];
ir_block *bb = &blocks[i];
if (bb->predecessors_count > 1) {
bool irreducible = 0;
uint32_t *p = &edges[bb->predecessors];
j = bb->predecessors_count;
do {
uint32_t pred = *p;
/* A join edge is one for which the predecessor does not
immediately dominate the successor. */
if (bb->idom != pred) {
/* In a loop back-edge (back-join edge), the successor dominates
the predecessor. */
if (ir_dominates(blocks, i, pred)) {
if (!ir_worklist_len(&work)) {
ir_bitset_clear(work.visited, ir_bitset_len(ir_worklist_capasity(&work)));
}
blocks[pred].loop_header = 0; /* support for merged loops */
ir_worklist_push(&work, pred);
} else {
/* Otherwise it's a cross-join edge. See if it's a branch
to an ancestor on the DJ spanning tree. */
if (entry_times[pred] > entry_times[i] && exit_times[pred] < exit_times[i]) {
irreducible = 1;
}
}
}
p++;
} while (--j);
if (UNEXPECTED(irreducible)) {
// TODO: Support for irreducible loops ???
bb->flags |= IR_BB_IRREDUCIBLE_LOOP;
ctx->flags2 |= IR_IRREDUCIBLE_CFG;
while (ir_worklist_len(&work)) {
ir_worklist_pop(&work);
}
} else if (ir_worklist_len(&work)) {
bb->flags |= IR_BB_LOOP_HEADER;
ctx->flags2 |= IR_CFG_HAS_LOOPS;
bb->loop_depth = 1;
while (ir_worklist_len(&work)) {
j = ir_worklist_pop(&work);
while (blocks[j].loop_header > 0) {
j = blocks[j].loop_header;
}