So, you've noticed that your method of handling phi's while cloning
doesn't handle phi's that point to other phi's in the same block.
Particularly, something like:
a = phi(b, ...)
b = phi(a, ...)
which is supposed to swap a and b each iteration. Here's a better
strategy which should be simpler than this and fixes that problem.
Create a new remap_table for each iteration of the loop. On the first
iteration, make all the phi nodes remap to their pre-loop sources
before cloning the body. On each successive iteration, make each phi
node map to what the *old* remap table (from the previous iteration)
says that it's source from the previous iteration remaps to. In
pseudocode:
nir_cf_list loop_body;
extract loop body into loop_body
move loop header instructions (minus phi nodes) into loop_body
struct hash_table *old_remap_table = NULL, *remap_table;
for each iteration:
remap_table = new dictionary;
for each phi in original loop:
if old_remap_table:
remap_table[phi] = old_remap_table[phi source pointing to
end of loop]
else:
remap_table[phi] = phi source pointing to block before loop
nir_cf_list cloned_body;
clone loop_body to cloned_body using remap_table
insert cloned_body before loop
delete loop_body
delete loop
This should eliminate the need to expose nir_cf_list_cleanup(),
stitch_blocks(), etc. publicly as well as the previous patch, and it
should handle the phi swapping case correctly.
On Mon, Aug 29, 2016 at 12:59 AM, Timothy Arceri
<timothy.arc...@collabora.com> wrote:
> ---
> src/compiler/nir/nir.h | 3 +++
> src/compiler/nir/nir_clone.c | 64
> +++++++++++++++++++++++++++++++++++++++-----
> 2 files changed, 60 insertions(+), 7 deletions(-)
>
> diff --git a/src/compiler/nir/nir.h b/src/compiler/nir/nir.h
> index 0ab3ebc..9083bd0 100644
> --- a/src/compiler/nir/nir.h
> +++ b/src/compiler/nir/nir.h
> @@ -2372,6 +2372,9 @@ void nir_print_instr(const nir_instr *instr, FILE *fp);
>
> nir_shader *nir_shader_clone(void *mem_ctx, const nir_shader *s);
> nir_function_impl *nir_function_impl_clone(const nir_function_impl *fi);
> +void nir_clone_loop_list(struct exec_list *dst, const struct exec_list *list,
> + struct hash_table *remap_table,
> + struct hash_table *phi_remap, nir_shader *ns);
> nir_constant *nir_constant_clone(const nir_constant *c, nir_variable *var);
> nir_variable *nir_variable_clone(const nir_variable *c, nir_shader *shader);
>
> diff --git a/src/compiler/nir/nir_clone.c b/src/compiler/nir/nir_clone.c
> index 8808333..071afc9 100644
> --- a/src/compiler/nir/nir_clone.c
> +++ b/src/compiler/nir/nir_clone.c
> @@ -35,9 +35,17 @@ typedef struct {
> /* True if we are cloning an entire shader. */
> bool global_clone;
>
> + /* This allows us to clone a loop body without having to add srcs from
> + * outside the loop to the remap table. This is useful for loop unrolling.
> + */
> + bool allow_remap_fallback;
> +
> /* maps orig ptr -> cloned ptr: */
> struct hash_table *remap_table;
>
> + /* used for remaping when cloning loop body for loop unrolling */
> + struct hash_table *phi_remap_table;
> +
> /* List of phi sources. */
> struct list_head phi_srcs;
>
> @@ -46,11 +54,20 @@ typedef struct {
> } clone_state;
>
> static void
> -init_clone_state(clone_state *state, bool global)
> +init_clone_state(clone_state *state, struct hash_table *remap_table,
> + bool global, bool allow_remap_fallback)
> {
> state->global_clone = global;
> - state->remap_table = _mesa_hash_table_create(NULL, _mesa_hash_pointer,
> - _mesa_key_pointer_equal);
> + state->allow_remap_fallback = allow_remap_fallback;
> +
> + state->phi_remap_table = NULL;
> + if (remap_table) {
> + state->remap_table = remap_table;
> + } else {
> + state->remap_table = _mesa_hash_table_create(NULL, _mesa_hash_pointer,
> + _mesa_key_pointer_equal);
> + }
> +
> list_inithead(&state->phi_srcs);
> }
>
> @@ -72,16 +89,32 @@ _lookup_ptr(clone_state *state, const void *ptr, bool
> global)
> return (void *)ptr;
>
> entry = _mesa_hash_table_search(state->remap_table, ptr);
> - assert(entry && "Failed to find pointer!");
> if (!entry)
> - return NULL;
> + return state->allow_remap_fallback ? (void *)ptr : NULL;
>
> return entry->data;
> }
>
> +/**
> + * Updates a phi remap table used for unrolling loops.
> + */
> +static void
> +update_phi_remap_table(clone_state *state, const void *ptr, void *nptr)
> +{
> + if (state->phi_remap_table == NULL)
> + return;
> +
> + struct hash_entry *hte;
> + hash_table_foreach(state->phi_remap_table, hte) {
> + if (hte->data == ptr)
> + hte->data = nptr;
> + }
> +}
> +
> static void
> add_remap(clone_state *state, void *nptr, const void *ptr)
> {
> + update_phi_remap_table(state, ptr, nptr);
> _mesa_hash_table_insert(state->remap_table, ptr, nptr);
> }
>
> @@ -613,6 +646,23 @@ fixup_phi_srcs(clone_state *state)
> assert(list_empty(&state->phi_srcs));
> }
>
> +void
> +nir_clone_loop_list(struct exec_list *dst, const struct exec_list *list,
> + struct hash_table *remap_table,
> + struct hash_table *phi_remap, nir_shader *ns)
> +{
> + clone_state state;
> + init_clone_state(&state, remap_table, false, true);
> +
> + /* We use the same shader */
> + state.ns = ns;
> + state.phi_remap_table = phi_remap;
> +
> + clone_cf_list(&state, dst, list);
> +
> + fixup_phi_srcs(&state);
> +}
> +
> static nir_function_impl *
> clone_function_impl(clone_state *state, const nir_function_impl *fi)
> {
> @@ -646,7 +696,7 @@ nir_function_impl *
> nir_function_impl_clone(const nir_function_impl *fi)
> {
> clone_state state;
> - init_clone_state(&state, false);
> + init_clone_state(&state, NULL, false, false);
>
> /* We use the same shader */
> state.ns = fi->function->shader;
> @@ -686,7 +736,7 @@ nir_shader *
> nir_shader_clone(void *mem_ctx, const nir_shader *s)
> {
> clone_state state;
> - init_clone_state(&state, true);
> + init_clone_state(&state, NULL, true, false);
>
> nir_shader *ns = nir_shader_create(mem_ctx, s->stage, s->options);
> state.ns = ns;
> --
> 2.7.4
>
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> mesa-dev@lists.freedesktop.org
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