From a3b6d05a3b3cd412541c9de2488486b1aa00aede Mon Sep 17 00:00:00 2001
From: Ian Romanick <ian.d.romanick@intel.com>
Date: Wed, 22 Oct 2025 11:32:12 -0700
Subject: [PATCH] nir/opt_if: Specify which branches are valid for
 evaluate_if_condition

Reviewed-by: Rhys Perry <pendingchaos02@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/38321>
---
 src/compiler/nir/nir_opt_if.c | 30 ++++++++++++++++++++++--------
 1 file changed, 22 insertions(+), 8 deletions(-)

diff --git a/src/compiler/nir/nir_opt_if.c b/src/compiler/nir/nir_opt_if.c
index f2b0e7e9e88..c2df6876439 100644
--- a/src/compiler/nir/nir_opt_if.c
+++ b/src/compiler/nir/nir_opt_if.c
@@ -834,14 +834,27 @@ opt_if_phi_is_condition(nir_builder *b, nir_if *nif)
    return progress;
 }
 
+enum branch_to_eval {
+   either_branch,
+   then_branch,
+   else_branch
+};
+
 static bool
-evaluate_if_condition(nir_if *nif, nir_cursor cursor, bool *value, bool invert)
+evaluate_if_condition(nir_if *nif, nir_cursor cursor, bool *value, bool invert,
+                      enum branch_to_eval branch)
 {
    nir_block *use_block = nir_cursor_current_block(cursor);
    if (nir_block_dominates(nir_if_first_then_block(nif), use_block)) {
+      if (branch == else_branch)
+         return false;
+
       *value = !invert;
       return true;
    } else if (nir_block_dominates(nir_if_first_else_block(nif), use_block)) {
+      if (branch == then_branch)
+         return false;
+
       *value = invert;
       return true;
    } else {
@@ -922,11 +935,12 @@ clone_alu_and_replace_src_defs(nir_builder *b, const nir_alu_instr *alu,
  */
 static bool
 propagate_condition_eval(nir_builder *b, nir_if *nif, nir_src *use_src,
-                         nir_src *alu_use, nir_alu_instr *alu, bool invert)
+                         nir_src *alu_use, nir_alu_instr *alu, bool invert,
+                         enum branch_to_eval branch)
 {
    bool bool_value;
    b->cursor = nir_before_src(alu_use);
-   if (!evaluate_if_condition(nif, b->cursor, &bool_value, invert))
+   if (!evaluate_if_condition(nif, b->cursor, &bool_value, invert, branch))
       return false;
 
    nir_def *def[NIR_MAX_VEC_COMPONENTS] = { 0 };
@@ -966,14 +980,14 @@ can_propagate_through_alu(nir_src *src)
 
 static bool
 evaluate_condition_use(nir_builder *b, nir_if *nif, nir_src *use_src,
-                       bool invert)
+                       bool invert, enum branch_to_eval branch)
 {
    bool progress = false;
 
    b->cursor = nir_before_src(use_src);
 
    bool bool_value;
-   if (evaluate_if_condition(nif, b->cursor, &bool_value, invert)) {
+   if (evaluate_if_condition(nif, b->cursor, &bool_value, invert, branch)) {
       /* Rewrite use to use const */
       nir_src_rewrite(use_src, nir_imm_bool(b, bool_value));
       progress = true;
@@ -984,7 +998,7 @@ evaluate_condition_use(nir_builder *b, nir_if *nif, nir_src *use_src,
 
       nir_foreach_use_including_if_safe(alu_use, &alu->def) {
          progress |= propagate_condition_eval(b, nif, use_src, alu_use, alu,
-                                              invert);
+                                              invert, branch);
       }
    }
 
@@ -999,7 +1013,7 @@ opt_if_evaluate_condition_use(nir_builder *b, nir_if *nif)
    /* Evaluate any uses of the if condition inside the if branches */
    nir_foreach_use_including_if_safe(use_src, nif->condition.ssa) {
       if (!(nir_src_is_if(use_src) && nir_src_parent_if(use_src) == nif))
-         progress |= evaluate_condition_use(b, nif, use_src, false);
+         progress |= evaluate_condition_use(b, nif, use_src, false, either_branch);
    }
 
    nir_alu_instr *alu = nir_src_as_alu_instr(nif->condition);
@@ -1019,7 +1033,7 @@ opt_if_evaluate_condition_use(nir_builder *b, nir_if *nif)
        */
       nir_foreach_use_including_if_safe(use_src, alu->src[0].src.ssa) {
          if (nir_src_is_if(use_src) || nir_src_parent_instr(use_src) != &alu->instr)
-            progress |= evaluate_condition_use(b, nif, use_src, true);
+            progress |= evaluate_condition_use(b, nif, use_src, true, either_branch);
       }
    }