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nir/phi_builder: Don't recurse in value_get_block_def

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In some programs, we can have very deep dominance trees and the recursion
can cause us to risk stack overflows.  Instead, we replace the recursion
with a pair of loops, one at the start and one at the end.  This is
functionally equivalent to what we had before and it's actually a bit
easier to read in the new form without the recursion.

Signed-off-by: Jason Ekstrand <jason@jlekstrand.net>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=97225
Reviewed-by: Connor Abbott <cwabbott0@gmail.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>
This commit is contained in:
Jason Ekstrand
2016-08-24 21:49:10 -07:00
parent 3eddf5219e
commit 78715c7211
1 changed files with 36 additions and 29 deletions
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src/compiler/nir/nir_phi_builder.c
+36 -29
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@@ -172,31 +172,27 @@ nir_ssa_def *
nir_phi_builder_value_get_block_def(struct nir_phi_builder_value *val,
nir_block *block)
{
/* For each block, we have one of three types of values */
if (val->defs[block->index] == NULL) {
/* NULL indicates that we have no SSA def for this block. */
if (block->imm_dom) {
/* Grab it from our immediate dominator. We'll stash it here for
* easy access later.
*/
val->defs[block->index] =
nir_phi_builder_value_get_block_def(val, block->imm_dom);
return val->defs[block->index];
} else {
/* No immediate dominator means that this block is either the
* start block or unreachable. In either case, the value is
* undefined so we need an SSA undef.
*/
nir_ssa_undef_instr *undef =
nir_ssa_undef_instr_create(val->builder->shader,
val->num_components,
val->bit_size);
nir_instr_insert(nir_before_cf_list(&val->builder->impl->body),
&undef->instr);
val->defs[block->index] = &undef->def;
return &undef->def;
}
} else if (val->defs[block->index] == NEEDS_PHI) {
/* Crawl up the dominance tree and find the closest dominator for which we
* have a valid ssa_def, if any.
*/
nir_block *dom = block;
while (dom && val->defs[dom->index] == NULL)
dom = dom->imm_dom;
nir_ssa_def *def;
if (dom == NULL) {
/* No dominator means either that we crawled to the top without ever
* finding a definition or that this block is unreachable. In either
* case, the value is undefined so we need an SSA undef.
*/
nir_ssa_undef_instr *undef =
nir_ssa_undef_instr_create(val->builder->shader,
val->num_components,
val->bit_size);
nir_instr_insert(nir_before_cf_list(&val->builder->impl->body),
&undef->instr);
def = &undef->def;
} else if (val->defs[dom->index] == NEEDS_PHI) {
/* The magic value NEEDS_PHI indicates that the block needs a phi node
* but none has been created. We need to create one now so we can
* return it to the caller.
@@ -218,17 +214,28 @@ nir_phi_builder_value_get_block_def(struct nir_phi_builder_value *val,
nir_phi_instr *phi = nir_phi_instr_create(val->builder->shader);
nir_ssa_dest_init(&phi->instr, &phi->dest, val->num_components,
val->bit_size, NULL);
phi->instr.block = block;
phi->instr.block = dom;
exec_list_push_tail(&val->phis, &phi->instr.node);
val->defs[block->index] = &phi->dest.ssa;
return &phi->dest.ssa;
def = &phi->dest.ssa;
} else {
/* In this case, we have an actual SSA def. It's either the result of a
* phi node created by the case above or one passed to us through
* nir_phi_builder_value_set_block_def().
*/
return val->defs[block->index];
def = val->defs[dom->index];
}
/* Walk the chain and stash the def in all of the applicable blocks. We do
* this for two reasons:
*
* 1) To speed up lookup next time even if the next time is called from a
* block that is not dominated by this one.
* 2) To avoid unneeded recreation of phi nodes and undefs.
*/
for (dom = block; dom && val->defs[dom->index] == NULL; dom = dom->imm_dom)
val->defs[dom->index] = def;
return def;
}
static int