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nir: Make nir_deref_path_init skip trivial casts

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In a NIR generated using SPIR-V initializers to variables, copy
propagation can end up transforming

    vec1 32 ssa_33 = deref_var &@1 (shared mat2x4)
    vec1 32 ssa_35 = mov ssa_33
    vec1 32 ssa_7 = deref_cast (mat2x4 *)ssa_35 (shared mat2x4)  /* ptr_stride=0 */

into

    vec1 32 ssa_33 = deref_var &@1 (shared mat2x4)
    vec1 32 ssa_7 = deref_cast (mat2x4 *)ssa_33 (shared mat2x4)  /* ptr_stride=0 */

Before the optimization, the "head" of a path of deref that uses ssa_7
will be the cast.  After, it will be the variable in ssa_33.  Since
the types are the same, this is a trivial cast that would be picked up
by nir_opt_deref.

If we need to compare such deref-chain after optimization with another
deref-chain for the same variable, the compare function will get
confused by the cast in the middle.

One alternative would be to add nir_opt_deref to places that compare
derefs, but that might not scale well, so skip the trivial casts when
generating the paths instead.

Motivated by the discussion in
https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3047#note_383660.

Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Tested-by: Marge Bot <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3420>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3420>
This commit is contained in:
Caio Marcelo de Oliveira Filho 2020-01-15 11:51:58 -08:00 • committed by Marge Bot
parent db19e96c8c
commit 8548fe19f0
1 changed files with 19 additions and 14 deletions
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33
src/compiler/nir/nir_deref.c
View file

@ -26,6 +26,19 @@
#include "nir_deref.h"
#include "util/hash_table.h"
static bool
is_trivial_deref_cast(nir_deref_instr *cast)
{
nir_deref_instr *parent = nir_src_as_deref(cast->parent);
if (!parent)
return false;
return cast->mode == parent->mode &&
cast->type == parent->type &&
cast->dest.ssa.num_components == parent->dest.ssa.num_components &&
cast->dest.ssa.bit_size == parent->dest.ssa.bit_size;
}
void
nir_deref_path_init(nir_deref_path *path,
nir_deref_instr *deref, void *mem_ctx)
@ -44,6 +57,8 @@ nir_deref_path_init(nir_deref_path *path,
*tail = NULL;
for (nir_deref_instr *d = deref; d; d = nir_deref_instr_parent(d)) {
if (d->deref_type == nir_deref_type_cast && is_trivial_deref_cast(d))
continue;
count++;
if (count <= max_short_path_len)
*(--head) = d;
@ -64,8 +79,11 @@ nir_deref_path_init(nir_deref_path *path,
path->path = ralloc_array(mem_ctx, nir_deref_instr *, count + 1);
head = tail = path->path + count;
*tail = NULL;
for (nir_deref_instr *d = deref; d; d = nir_deref_instr_parent(d))
for (nir_deref_instr *d = deref; d; d = nir_deref_instr_parent(d)) {
if (d->deref_type == nir_deref_type_cast && is_trivial_deref_cast(d))
continue;
*(--head) = d;
}
done:
assert(head == path->path);
@ -735,19 +753,6 @@ nir_rematerialize_derefs_in_use_blocks_impl(nir_function_impl *impl)
return state.progress;
}
static bool
is_trivial_deref_cast(nir_deref_instr *cast)
{
nir_deref_instr *parent = nir_src_as_deref(cast->parent);
if (!parent)
return false;
return cast->mode == parent->mode &&
cast->type == parent->type &&
cast->dest.ssa.num_components == parent->dest.ssa.num_components &&
cast->dest.ssa.bit_size == parent->dest.ssa.bit_size;
}
static bool
is_trivial_array_deref_cast(nir_deref_instr *cast)
{