[Mesa-dev] [PATCH 02/12] nir: limit copy propagation inside loops
Timothy Arceri
timothy.arceri at collabora.com
Sat Aug 27 06:03:24 UTC 2016
Don't do copy propagation inside loops until after we try
unrolling them.
This helps avoid propagating everything to the phis which
makes loop unrolling more difficult.
For example without this:
loop {
block block_1:
/* preds: block_0 block_4 */
vec1 32 ssa_10 = phi block_0: ssa_5, block_4: ssa_15
vec1 32 ssa_11 = phi block_0: ssa_6, block_4: ssa_17
vec1 32 ssa_12 = phi block_0: ssa_7, block_4: ssa_18
vec1 32 ssa_13 = phi block_0: ssa_8, block_4: ssa_19
vec1 32 ssa_14 = phi block_0: ssa_9, block_4: ssa_20
vec1 32 ssa_15 = iadd ssa_10, ssa_2
vec1 32 ssa_16 = ige ssa_15, ssa_1
/* succs: block_2 block_3 */
if ssa_16 {
block block_2:
/* preds: block_1 */
break
/* succs: block_5 */
} else {
block block_3:
/* preds: block_1 */
/* succs: block_4 */
}
block block_4:
/* preds: block_3 */
vec1 32 ssa_17 = imov ssa_12
vec1 32 ssa_18 = imov ssa_13
vec1 32 ssa_19 = imov ssa_14
vec1 32 ssa_20 = imov ssa_11
/* succs: block_1 */
}
Will end up as:
loop {
/* preds: block_0 block_4 */
block block_1:
vec1 32 ssa_10 = phi block_0: ssa_5, block_4: ssa_15
vec1 32 ssa_11 = phi block_0: ssa_6, block_4: ssa_12
vec1 32 ssa_12 = phi block_0: ssa_7, block_4: ssa_13
vec1 32 ssa_13 = phi block_0: ssa_8, block_4: ssa_14
vec1 32 ssa_14 = phi block_0: ssa_9, block_4: ssa_11
vec1 32 ssa_15 = iadd ssa_10, ssa_2
vec1 32 ssa_16 = ige ssa_15, ssa_1
/* succs: block_2 block_3 */
if ssa_16 {
block block_2:
/* preds: block_1 */
break
/* succs: block_5 */
} else {
block block_3:
/* preds: block_1 */
/* succs: block_4 */
}
block block_4:
/* preds: block_3 */
/* succs: block_1 */
}
---
src/compiler/nir/nir.h | 2 +-
src/compiler/nir/nir_opt_copy_propagate.c | 47 ++++++++++++++++++++-----------
src/mesa/drivers/dri/i965/brw_nir.c | 6 ++--
3 files changed, 35 insertions(+), 20 deletions(-)
diff --git a/src/compiler/nir/nir.h b/src/compiler/nir/nir.h
index 5e527d8..e3e06b1 100644
--- a/src/compiler/nir/nir.h
+++ b/src/compiler/nir/nir.h
@@ -2562,7 +2562,7 @@ bool nir_opt_constant_folding(nir_shader *shader);
bool nir_opt_global_to_local(nir_shader *shader);
-bool nir_copy_prop(nir_shader *shader);
+bool nir_copy_prop(nir_shader *shader, bool prop_loops);
bool nir_opt_cse(nir_shader *shader);
diff --git a/src/compiler/nir/nir_opt_copy_propagate.c b/src/compiler/nir/nir_opt_copy_propagate.c
index c26e07f..12daeb6 100644
--- a/src/compiler/nir/nir_opt_copy_propagate.c
+++ b/src/compiler/nir/nir_opt_copy_propagate.c
@@ -99,11 +99,14 @@ is_swizzleless_move(nir_alu_instr *instr)
}
static bool
-copy_prop_src(nir_src *src, nir_instr *parent_instr, nir_if *parent_if)
+copy_prop_src(nir_src *src, nir_instr *parent_instr, nir_if *parent_if,
+ bool prop_loops)
{
if (!src->is_ssa) {
- if (src->reg.indirect)
- return copy_prop_src(src->reg.indirect, parent_instr, parent_if);
+ if (src->reg.indirect) {
+ return copy_prop_src(src->reg.indirect, parent_instr, parent_if,
+ prop_loops);
+ }
return false;
}
@@ -125,6 +128,14 @@ copy_prop_src(nir_src *src, nir_instr *parent_instr, nir_if *parent_if)
if (phi->dest.ssa.num_components !=
alu_instr->src[0].src.ssa->num_components)
return false;
+
+ /* Avoid propagating moves inside a loop into phis which makes
+ * unrolling difficult.
+ */
+ if (!prop_loops) {
+ if (phi->instr.block->cf_node.parent->type == nir_cf_node_loop)
+ return false;
+ }
}
if (parent_instr) {
@@ -140,13 +151,14 @@ copy_prop_src(nir_src *src, nir_instr *parent_instr, nir_if *parent_if)
}
static bool
-copy_prop_alu_src(nir_alu_instr *parent_alu_instr, unsigned index)
+copy_prop_alu_src(nir_alu_instr *parent_alu_instr, unsigned index,
+ bool prop_loops)
{
nir_alu_src *src = &parent_alu_instr->src[index];
if (!src->src.is_ssa) {
if (src->src.reg.indirect)
return copy_prop_src(src->src.reg.indirect, &parent_alu_instr->instr,
- NULL);
+ NULL, prop_loops);
return false;
}
@@ -195,6 +207,7 @@ copy_prop_alu_src(nir_alu_instr *parent_alu_instr, unsigned index)
typedef struct {
nir_instr *parent_instr;
+ bool prop_loops;
bool progress;
} copy_prop_state;
@@ -202,25 +215,26 @@ static bool
copy_prop_src_cb(nir_src *src, void *_state)
{
copy_prop_state *state = (copy_prop_state *) _state;
- while (copy_prop_src(src, state->parent_instr, NULL))
+ while (copy_prop_src(src, state->parent_instr, NULL, state->prop_loops))
state->progress = true;
return true;
}
static bool
-copy_prop_instr(nir_instr *instr)
+copy_prop_instr(nir_instr *instr, bool prop_loops)
{
if (instr->type == nir_instr_type_alu) {
nir_alu_instr *alu_instr = nir_instr_as_alu(instr);
bool progress = false;
for (unsigned i = 0; i < nir_op_infos[alu_instr->op].num_inputs; i++)
- while (copy_prop_alu_src(alu_instr, i))
+ while (copy_prop_alu_src(alu_instr, i, prop_loops))
progress = true;
if (!alu_instr->dest.dest.is_ssa && alu_instr->dest.dest.reg.indirect)
- while (copy_prop_src(alu_instr->dest.dest.reg.indirect, instr, NULL))
+ while (copy_prop_src(alu_instr->dest.dest.reg.indirect, instr, NULL,
+ prop_loops))
progress = true;
return progress;
@@ -229,30 +243,31 @@ copy_prop_instr(nir_instr *instr)
copy_prop_state state;
state.parent_instr = instr;
state.progress = false;
+ state.prop_loops = prop_loops;
nir_foreach_src(instr, copy_prop_src_cb, &state);
return state.progress;
}
static bool
-copy_prop_if(nir_if *if_stmt)
+copy_prop_if(nir_if *if_stmt, bool prop_loops)
{
- return copy_prop_src(&if_stmt->condition, NULL, if_stmt);
+ return copy_prop_src(&if_stmt->condition, NULL, if_stmt, prop_loops);
}
static bool
-nir_copy_prop_impl(nir_function_impl *impl)
+nir_copy_prop_impl(nir_function_impl *impl, bool prop_loops)
{
bool progress = false;
nir_foreach_block(block, impl) {
nir_foreach_instr(instr, block) {
- if (copy_prop_instr(instr))
+ if (copy_prop_instr(instr, prop_loops))
progress = true;
}
nir_if *if_stmt = nir_block_get_following_if(block);
- if (if_stmt && copy_prop_if(if_stmt))
+ if (if_stmt && copy_prop_if(if_stmt, prop_loops))
progress = true;
}
@@ -265,12 +280,12 @@ nir_copy_prop_impl(nir_function_impl *impl)
}
bool
-nir_copy_prop(nir_shader *shader)
+nir_copy_prop(nir_shader *shader, bool prop_loops)
{
bool progress = false;
nir_foreach_function(function, shader) {
- if (function->impl && nir_copy_prop_impl(function->impl))
+ if (function->impl && nir_copy_prop_impl(function->impl, prop_loops))
progress = true;
}
diff --git a/src/mesa/drivers/dri/i965/brw_nir.c b/src/mesa/drivers/dri/i965/brw_nir.c
index 8aec0d3..6122c2a 100644
--- a/src/mesa/drivers/dri/i965/brw_nir.c
+++ b/src/mesa/drivers/dri/i965/brw_nir.c
@@ -374,13 +374,13 @@ nir_optimize(nir_shader *nir, bool is_scalar)
OPT_V(nir_lower_alu_to_scalar);
}
- OPT(nir_copy_prop);
+ OPT(nir_copy_prop, false);
if (is_scalar) {
OPT_V(nir_lower_phis_to_scalar);
}
- OPT(nir_copy_prop);
+ OPT(nir_copy_prop, false);
OPT(nir_opt_dce);
OPT(nir_opt_cse);
OPT(nir_opt_peephole_select);
@@ -495,7 +495,7 @@ brw_postprocess_nir(nir_shader *nir,
OPT(nir_lower_locals_to_regs);
OPT_V(nir_lower_to_source_mods);
- OPT(nir_copy_prop);
+ OPT(nir_copy_prop, true);
OPT(nir_opt_dce);
if (unlikely(debug_enabled)) {
--
2.7.4
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