[Mesa-dev] [PATCH 07/31] nir/opt_if: Rework condition propagation

[Jason Ekstrand]

Instead of doing our own constant folding, we just emit instructions and
let constant folding happen.  This is substantially simpler and lets us
use the nir_imm_bool helper instead of dealing with the const_value's
ourselves.
---
 src/compiler/nir/nir_opt_if.c | 91 ++++++++++++-----------------------
 1 file changed, 30 insertions(+), 61 deletions(-)

diff --git a/src/compiler/nir/nir_opt_if.c b/src/compiler/nir/nir_opt_if.c
index 0c94aa170b5..60368a0259e 100644
--- a/src/compiler/nir/nir_opt_if.c
+++ b/src/compiler/nir/nir_opt_if.c
@@ -377,31 +377,15 @@ opt_if_loop_terminator(nir_if *nif)
    return true;
 }
 
-static void
-replace_if_condition_use_with_const(nir_builder *b, nir_src *use,
-                                    nir_const_value nir_boolean,
-                                    bool if_condition)
-{
-   /* Create const */
-   nir_ssa_def *const_def = nir_build_imm(b, 1, 32, nir_boolean);
-
-   /* Rewrite use to use const */
-   nir_src new_src = nir_src_for_ssa(const_def);
-   if (if_condition)
-      nir_if_rewrite_condition(use->parent_if, new_src);
-   else
-      nir_instr_rewrite_src(use->parent_instr, use, new_src);
-}
-
 static bool
-evaluate_if_condition(nir_if *nif, nir_cursor cursor, uint32_t *value)
+evaluate_if_condition(nir_if *nif, nir_cursor cursor, bool *value)
 {
    nir_block *use_block = nir_cursor_current_block(cursor);
    if (nir_block_dominates(nir_if_first_then_block(nif), use_block)) {
-      *value = NIR_TRUE;
+      *value = true;
       return true;
    } else if (nir_block_dominates(nir_if_first_else_block(nif), use_block)) {
-      *value = NIR_FALSE;
+      *value = false;
       return true;
    } else {
       return false;
@@ -460,52 +444,31 @@ propagate_condition_eval(nir_builder *b, nir_if *nif, nir_src *use_src,
                          nir_src *alu_use, nir_alu_instr *alu,
                          bool is_if_condition)
 {
-   bool progress = false;
+   bool bool_value;
+   if (!evaluate_if_condition(nif, b->cursor, &bool_value))
+      return false;
 
-   nir_const_value bool_value;
    b->cursor = nir_before_src(alu_use, is_if_condition);
-   if (nir_op_infos[alu->op].num_inputs == 1) {
-      assert(alu->op == nir_op_inot || alu->op == nir_op_b2i);
-
-      if (evaluate_if_condition(nif, b->cursor, &bool_value.u32[0])) {
-         assert(nir_src_bit_size(alu->src[0].src) == 32);
-
-         nir_const_value result =
-            nir_eval_const_opcode(alu->op, 1, 32, &bool_value);
 
-         replace_if_condition_use_with_const(b, alu_use, result,
-                                             is_if_condition);
-         progress = true;
+   nir_ssa_def *def[2] = { };
+   for (unsigned i = 0; i < nir_op_infos[alu->op].num_inputs; i++) {
+      if (alu->src[i].src.ssa == use_src->ssa) {
+         def[i] = nir_imm_bool(b, bool_value);
+      } else {
+         def[i] = alu->src[i].src.ssa;
       }
-   } else {
-      assert(alu->op == nir_op_ior || alu->op == nir_op_iand);
-
-      if (evaluate_if_condition(nif, b->cursor, &bool_value.u32[0])) {
-         nir_ssa_def *def[2];
-         for (unsigned i = 0; i < 2; i++) {
-            if (alu->src[i].src.ssa == use_src->ssa) {
-               def[i] = nir_build_imm(b, 1, 32, bool_value);
-            } else {
-               def[i] = alu->src[i].src.ssa;
-            }
-         }
-
-         nir_ssa_def *nalu =
-            nir_build_alu(b, alu->op, def[0], def[1], NULL, NULL);
-
-         /* Rewrite use to use new alu instruction */
-         nir_src new_src = nir_src_for_ssa(nalu);
+   }
+   nir_ssa_def *nalu = nir_build_alu(b, alu->op, def[0], def[1], NULL, NULL);
 
-         if (is_if_condition)
-            nir_if_rewrite_condition(alu_use->parent_if, new_src);
-         else
-            nir_instr_rewrite_src(alu_use->parent_instr, alu_use, new_src);
+   /* Rewrite use to use new alu instruction */
+   nir_src new_src = nir_src_for_ssa(nalu);
 
-         progress = true;
-      }
-   }
+   if (is_if_condition)
+      nir_if_rewrite_condition(alu_use->parent_if, new_src);
+   else
+      nir_instr_rewrite_src(alu_use->parent_instr, alu_use, new_src);
 
-   return progress;
+   return true;
 }
 
 static bool
@@ -527,11 +490,17 @@ evaluate_condition_use(nir_builder *b, nir_if *nif, nir_src *use_src,
 {
    bool progress = false;
 
-   nir_const_value value;
    b->cursor = nir_before_src(use_src, is_if_condition);
 
-   if (evaluate_if_condition(nif, b->cursor, &value.u32[0])) {
-      replace_if_condition_use_with_const(b, use_src, value, is_if_condition);
+   bool bool_value;
+   if (evaluate_if_condition(nif, b->cursor, &bool_value)) {
+      /* Rewrite use to use const */
+      nir_src imm_src = nir_src_for_ssa(nir_imm_bool(b, bool_value));
+      if (is_if_condition)
+         nir_if_rewrite_condition(use_src->parent_if, imm_src);
+      else
+         nir_instr_rewrite_src(use_src->parent_instr, use_src, imm_src);
+
       progress = true;
    }
 
-- 
2.19.1