glsl: Add flag to disable part of do_vec_index_to_cond_assign

As of ca63a5ed3e ("glsl: fix interpolateAtXxx(some_vec[idx], ...)  with
dynamic idx"), this lowering pass does two things.  It converts
ir_binop_vector_extract to an if-ladder to select the dynamically
indexed component, and it extracts a ir_binop_vector_extract from the
source of an interpolateAt function and applies to the result instead.

This change adds a flag to disable the former behavior.  The latter is
still useful, but NIR has better (and soon even better) ways of doing
the former.

Reviewed-by: Matt Turner <mattst88@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/16440>

src/compiler/glsl/ir_optimization.h

@@ -116,7 +116,7 @@ bool do_minmax_prune(exec_list *instructions);
 bool do_structure_splitting(exec_list *instructions);
 bool optimize_swizzles(exec_list *instructions);
 bool do_tree_grafting(exec_list *instructions);
-bool do_vec_index_to_cond_assign(exec_list *instructions);
+bool do_vec_index_to_cond_assign(exec_list *instructions, bool lower_extracts);
 bool do_vec_index_to_swizzle(exec_list *instructions);
 bool lower_discard(exec_list *instructions);
 void lower_discard_flow(exec_list *instructions);

src/compiler/glsl/lower_vec_index_to_cond_assign.cpp

@@ -53,8 +53,8 @@ namespace {
 
 class ir_vec_index_to_cond_assign_visitor : public ir_hierarchical_visitor {
 public:
-   ir_vec_index_to_cond_assign_visitor()
-      : progress(false)
+   ir_vec_index_to_cond_assign_visitor(bool _lower_extracts)
+      : lower_extracts(_lower_extracts), progress(false)
    {
       /* empty */
    }
@@ -73,6 +73,7 @@ public:
    virtual ir_visitor_status visit_enter(ir_call *);
    virtual ir_visitor_status visit_enter(ir_if *);
 
+   bool lower_extracts;
    bool progress;
 };
 
@@ -191,13 +192,20 @@ ir_vec_index_to_cond_assign_visitor::convert_vector_extract_to_cond_assign(ir_rv
          new(base_ir) ir_expression(expr->operation, vec_input->type,
                                     vec_input, expr->operands[1]);
 
+      if (lower_extracts) {
          return convert_vec_index_to_cond_assign(ralloc_parent(ir),
                                                  vec_interpolate,
                                                  interpolant->operands[1],
                                                  ir->type);
+      } else {
+         this->progress = true;
+         return new(base_ir) ir_expression(ir_binop_vector_extract, ir->type,
+                                           vec_interpolate,
+                                           interpolant->operands[1]);
+      }
    }
 
-   if (expr->operation != ir_binop_vector_extract)
+   if (!lower_extracts || expr->operation != ir_binop_vector_extract)
       return ir;
 
    return convert_vec_index_to_cond_assign(ralloc_parent(ir),
@@ -267,9 +275,9 @@ ir_vec_index_to_cond_assign_visitor::visit_enter(ir_if *ir)
 }
 
 bool
-do_vec_index_to_cond_assign(exec_list *instructions)
+do_vec_index_to_cond_assign(exec_list *instructions, bool lower_extracts)
 {
-   ir_vec_index_to_cond_assign_visitor v;
+   ir_vec_index_to_cond_assign_visitor v(lower_extracts);
 
    visit_list_elements(&v, instructions);
 

src/compiler/glsl/test_optpass.cpp

@@ -102,7 +102,7 @@ do_optimization(struct exec_list *ir, const char *optimization,
    } else if (strcmp(optimization, "do_tree_grafting") == 0) {
       return do_tree_grafting(ir);
    } else if (strcmp(optimization, "do_vec_index_to_cond_assign") == 0) {
-      return do_vec_index_to_cond_assign(ir);
+      return do_vec_index_to_cond_assign(ir, true);
    } else if (strcmp(optimization, "do_vec_index_to_swizzle") == 0) {
       return do_vec_index_to_swizzle(ir);
    } else if (strcmp(optimization, "lower_discard") == 0) {

src/mesa/state_tracker/st_glsl_to_ir.cpp

@@ -130,7 +130,7 @@ link_shader(struct gl_context *ctx, struct gl_shader_program *prog)
                             IMUL_HIGH_TO_MUL
                           : 0));
 
-      do_vec_index_to_cond_assign(ir);
+      do_vec_index_to_cond_assign(ir, true);
       lower_vector_insert(ir, true);
       if (options->MaxIfDepth == 0) {
          lower_discard(ir);