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nir/loop_analyze: Fix phi-of-identical-alu detection

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One issue was that the original version didn't check that swizzles
matched when comparing ALU instructions so it could end up matching
very different instructions.  Using the nir_instrs_equal function from
nir_instr_set.c which we use for CSE should be much more reliable.
Another was that the loop assumes it will only run two iterations which
may not be true.  If there's something which guarantees that this case
only happens for phis after ifs, it wasn't documented.

Fixes: 9e6b39e1d5 "nir: detect more induction variables"
Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>
This commit is contained in:
Jason Ekstrand 2019-06-20 16:13:39 -05:00
parent 6e984bcb92
commit 9f7ffe41dd
1 changed files with 29 additions and 26 deletions
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55
src/compiler/nir/nir_loop_analyze.c
View file

@ -274,6 +274,31 @@ compute_invariance_information(loop_info_state *state)
}
}
/* If all of the instruction sources point to identical ALU instructions (as
* per nir_instrs_equal), return one of the ALU instructions. Otherwise,
* return NULL.
*/
static nir_alu_instr *
phi_instr_as_alu(nir_phi_instr *phi)
{
nir_alu_instr *first = NULL;
nir_foreach_phi_src(src, phi) {
assert(src->src.is_ssa);
if (src->src.ssa->parent_instr->type != nir_instr_type_alu)
return NULL;
nir_alu_instr *alu = nir_instr_as_alu(src->src.ssa->parent_instr);
if (first == NULL) {
first = alu;
} else {
if (!nir_instrs_equal(&first->instr, &alu->instr))
return NULL;
}
}
return first;
}
static bool
compute_induction_information(loop_info_state *state)
{
@ -313,33 +338,11 @@ compute_induction_information(loop_info_state *state)
if (is_var_phi(src_var)) {
nir_phi_instr *src_phi =
nir_instr_as_phi(src_var->def->parent_instr);
nir_op alu_op = nir_num_opcodes; /* avoid uninitialized warning */
nir_ssa_def *alu_srcs[2] = {0};
nir_foreach_phi_src(src2, src_phi) {
nir_loop_variable *src_var2 =
get_loop_var(src2->src.ssa, state);
if (!src_var2->in_if_branch || !is_var_alu(src_var2))
nir_alu_instr *src_phi_alu = phi_instr_as_alu(src_phi);
if (src_phi_alu) {
src_var = get_loop_var(&src_phi_alu->dest.dest.ssa, state);
if (!src_var->in_if_branch)
break;
nir_alu_instr *alu =
nir_instr_as_alu(src_var2->def->parent_instr);
if (nir_op_infos[alu->op].num_inputs != 2)
break;
if (alu->src[0].src.ssa == alu_srcs[0] &&
alu->src[1].src.ssa == alu_srcs[1] &&
alu->op == alu_op) {
/* Both branches perform the same calculation so we can use
* one of them to find the induction variable.
*/
src_var = src_var2;
} else {
alu_srcs[0] = alu->src[0].src.ssa;
alu_srcs[1] = alu->src[1].src.ssa;
alu_op = alu->op;
}
}
}