Mesa (main): nir: Do peephole select on other instructions if the limit is ~0.

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Module: Mesa
Branch: main
Commit: 47804f53f991c3467671e05421df437b0f34eb22
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=47804f53f991c3467671e05421df437b0f34eb22

Author: Eric Anholt <eric at anholt.net>
Date:   Wed Aug 12 11:17:28 2020 -0700

nir: Do peephole select on other instructions if the limit is ~0.

limit==0 is the signal for "don't peephole anything but a move that will
be optimized aways."  limit > 0 is "up to N alu instructions may be moved
out."  nir-to-tgsi uses ~0 as the indicator of "No, we really need to
eliminate all if instructions" on hardware like i915 that doesn't have
control flow.

Reviewed-by: Jason Ekstrand <jason at jlekstrand.net>
Reviewed-by: Adam Jackson <ajax at redhat.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/11329>

---

 src/compiler/nir/nir_opt_peephole_select.c | 34 +++++++++++++++++++++++++++---
 1 file changed, 31 insertions(+), 3 deletions(-)

diff --git a/src/compiler/nir/nir_opt_peephole_select.c b/src/compiler/nir/nir_opt_peephole_select.c
index 62530ddd793..dec36670cbc 100644
--- a/src/compiler/nir/nir_opt_peephole_select.c
+++ b/src/compiler/nir/nir_opt_peephole_select.c
@@ -61,9 +61,37 @@
 
 static bool
 block_check_for_allowed_instrs(nir_block *block, unsigned *count,
-                               bool alu_ok, bool indirect_load_ok,
+                               unsigned limit, bool indirect_load_ok,
                                bool expensive_alu_ok)
 {
+   bool alu_ok = limit != 0;
+
+   /* Used on non-control-flow HW to flatten all IFs. */
+   if (limit == ~0) {
+      nir_foreach_instr(instr, block) {
+         switch (instr->type) {
+         case nir_instr_type_alu:
+         case nir_instr_type_deref:
+         case nir_instr_type_load_const:
+         case nir_instr_type_phi:
+         case nir_instr_type_ssa_undef:
+         case nir_instr_type_tex:
+            break;
+
+         case nir_instr_type_intrinsic:
+            if (!nir_intrinsic_can_reorder(nir_instr_as_intrinsic(instr)))
+               return false;
+            break;
+
+         case nir_instr_type_call:
+         case nir_instr_type_jump:
+         case nir_instr_type_parallel_copy:
+            return false;
+         }
+      }
+      return true;
+   }
+
    nir_foreach_instr(instr, block) {
       switch (instr->type) {
       case nir_instr_type_intrinsic: {
@@ -379,9 +407,9 @@ nir_opt_peephole_select_block(nir_block *block, nir_shader *shader,
 
    /* ... and those blocks must only contain "allowed" instructions. */
    unsigned count = 0;
-   if (!block_check_for_allowed_instrs(then_block, &count, limit != 0,
+   if (!block_check_for_allowed_instrs(then_block, &count, limit,
                                        indirect_load_ok, expensive_alu_ok) ||
-       !block_check_for_allowed_instrs(else_block, &count, limit != 0,
+       !block_check_for_allowed_instrs(else_block, &count, limit,
                                        indirect_load_ok, expensive_alu_ok))
       return false;