nir: Add an optional expression controlling nir_algebraic xforms.

This will be used so that we can customize the transforms for the target
GPU, so we don't un-lower expressions that had already been lowered (or
introduce new lowering transformations that not all GPUs want)

v2: Drop the complication of having the condition->index dictionary, since
    we don't actually expect there to be many different conditions (change
    by Kenneth).

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

src/glsl/nir/nir_algebraic.py

@@ -147,10 +147,23 @@ class Expression(Value):
 
 _optimization_ids = itertools.count()
 
+condition_list = ['true']
+
 class SearchAndReplace(object):
-   def __init__(self, search, replace):
+   def __init__(self, transform):
       self.id = _optimization_ids.next()
 
+      search = transform[0]
+      replace = transform[1]
+      if len(transform) > 2:
+         self.condition = transform[2]
+      else:
+         self.condition = 'true'
+
+      if self.condition not in condition_list:
+         condition_list.append(self.condition)
+      self.condition_index = condition_list.index(self.condition)
+
       varset = VarSet()
       if isinstance(search, Expression):
          self.search = search
@@ -171,6 +184,7 @@ _algebraic_pass_template = mako.template.Template("""
 struct transform {
    const nir_search_expression *search;
    const nir_search_value *replace;
+   unsigned condition_offset;
 };
 
 % for (opcode, xform_list) in xform_dict.iteritems():
@@ -181,7 +195,7 @@ struct transform {
 
 static const struct transform ${pass_name}_${opcode}_xforms[] = {
 % for xform in xform_list:
-   { &${xform.search.name}, ${xform.replace.c_ptr} },
+   { &${xform.search.name}, ${xform.replace.c_ptr}, ${xform.condition_index} },
 % endfor
 };
 % endfor
@@ -189,6 +203,7 @@ static const struct transform ${pass_name}_${opcode}_xforms[] = {
 struct opt_state {
    void *mem_ctx;
    bool progress;
+   const bool *condition_flags;
 };
 
 static bool
@@ -209,7 +224,8 @@ ${pass_name}_block(nir_block *block, void *void_state)
       case nir_op_${opcode}:
          for (unsigned i = 0; i < ARRAY_SIZE(${pass_name}_${opcode}_xforms); i++) {
             const struct transform *xform = &${pass_name}_${opcode}_xforms[i];
-            if (nir_replace_instr(alu, xform->search, xform->replace,
+            if (state->condition_flags[xform->condition_offset] &&
+                nir_replace_instr(alu, xform->search, xform->replace,
                                   state->mem_ctx)) {
                state->progress = true;
                break;
@@ -226,12 +242,13 @@ ${pass_name}_block(nir_block *block, void *void_state)
 }
 
 static bool
-${pass_name}_impl(nir_function_impl *impl)
+${pass_name}_impl(nir_function_impl *impl, const bool *condition_flags)
 {
    struct opt_state state;
 
    state.mem_ctx = ralloc_parent(impl);
    state.progress = false;
+   state.condition_flags = condition_flags;
 
    nir_foreach_block(impl, ${pass_name}_block, &state);
 
@@ -242,14 +259,21 @@ ${pass_name}_impl(nir_function_impl *impl)
    return state.progress;
 }
 
+
 bool
 ${pass_name}(nir_shader *shader)
 {
    bool progress = false;
+   bool condition_flags[${len(condition_list)}];
+   const nir_shader_compiler_options *options = shader->options;
+
+   % for index, condition in enumerate(condition_list):
+   condition_flags[${index}] = ${condition};
+   % endfor
 
    nir_foreach_overload(shader, overload) {
       if (overload->impl)
-         progress |= ${pass_name}_impl(overload->impl);
+         progress |= ${pass_name}_impl(overload->impl, condition_flags);
    }
 
    return progress;
@@ -263,7 +287,7 @@ class AlgebraicPass(object):
 
       for xform in transforms:
          if not isinstance(xform, SearchAndReplace):
-            xform = SearchAndReplace(*xform)
+            xform = SearchAndReplace(xform)
 
          if xform.search.opcode not in self.xform_dict:
             self.xform_dict[xform.search.opcode] = []
@@ -272,4 +296,5 @@ class AlgebraicPass(object):
 
    def render(self):
       return _algebraic_pass_template.render(pass_name=self.pass_name,
-                                             xform_dict=self.xform_dict)
+                                             xform_dict=self.xform_dict,
+                                             condition_list=condition_list)