glsl: add is_lhs bool on ast_expression

Useful to know if a expression is the recipient of an assignment
or not, that would be used to (for example) raise warnings of
"use of uninitialized variable" without getting a false positive
when assigning first a variable.

By default the value is false, and it is assigned to true on
the following cases:
 * The lhs assignments subexpression
 * At ast_array_index, on the array itself.
 * While handling the method on an array, to avoid the warning
   calling array.length
 * When computed the cached test expression at test_to_hir, to
   avoid a duplicate warning on the test expression of a switch.

set_is_lhs setter is added, because in some cases (like ast_field_selection)
the value need to be propagated on the expression tree. To avoid doing the
propatagion if not needed, it skips if no primary_expression.identifier is
available.

v2: use a new bool on ast_expression, instead of a new parameter
    on ast_expression::hir (Timothy Arceri)

v3: fix style and some typos on comments, initialize is_lhs default value
    on constructor, to avoid a c++11 feature (Ian Romanick)

v4: some tweaks on comments (Timothy Arceri)

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=94129

Reviewed-by: Timothy Arceri <timothy.arceri@collabora.com>

src/compiler/glsl/ast.h

@@ -214,6 +214,7 @@ public:
       subexpressions[2] = NULL;
       primary_expression.identifier = identifier;
       this->non_lvalue_description = NULL;
+      this->is_lhs = false;
    }
 
    static const char *operator_string(enum ast_operators op);
@@ -263,6 +264,11 @@ public:
     * This pointer may be \c NULL.
     */
    const char *non_lvalue_description;
+
+   void set_is_lhs(bool new_value);
+
+private:
+   bool is_lhs;
 };
 
 class ast_expression_bin : public ast_expression {

src/compiler/glsl/ast_function.cpp

@@ -1727,6 +1727,10 @@ ast_function_expression::handle_method(exec_list *instructions,
    const char *method;
    method = field->primary_expression.identifier;
 
+   /* This would prevent to raise "uninitialized variable" warnings when
+    * calling array.length.
+    */
+   field->subexpressions[0]->set_is_lhs(true);
    op = field->subexpressions[0]->hir(instructions, state);
    if (strcmp(method, "length") == 0) {
       if (!this->expressions.is_empty()) {

src/compiler/glsl/ast_to_hir.cpp

@@ -1248,6 +1248,24 @@ ast_expression::hir_no_rvalue(exec_list *instructions,
    do_hir(instructions, state, false);
 }
 
+void
+ast_expression::set_is_lhs(bool new_value)
+{
+   /* is_lhs is tracked only to print "variable used uninitialized" warnings,
+    * if we lack a identifier we can just skip it.
+    */
+   if (this->primary_expression.identifier == NULL)
+      return;
+
+   this->is_lhs = new_value;
+
+   /* We need to go through the subexpressions tree to cover cases like
+    * ast_field_selection
+    */
+   if (this->subexpressions[0] != NULL)
+      this->subexpressions[0]->set_is_lhs(new_value);
+}
+
 ir_rvalue *
 ast_expression::do_hir(exec_list *instructions,
                        struct _mesa_glsl_parse_state *state,
@@ -1323,6 +1341,7 @@ ast_expression::do_hir(exec_list *instructions,
       break;
 
    case ast_assign: {
+      this->subexpressions[0]->set_is_lhs(true);
       op[0] = this->subexpressions[0]->hir(instructions, state);
       op[1] = this->subexpressions[1]->hir(instructions, state);
 
@@ -1592,6 +1611,7 @@ ast_expression::do_hir(exec_list *instructions,
    case ast_div_assign:
    case ast_add_assign:
    case ast_sub_assign: {
+      this->subexpressions[0]->set_is_lhs(true);
       op[0] = this->subexpressions[0]->hir(instructions, state);
       op[1] = this->subexpressions[1]->hir(instructions, state);
 
@@ -1618,6 +1638,7 @@ ast_expression::do_hir(exec_list *instructions,
    }
 
    case ast_mod_assign: {
+      this->subexpressions[0]->set_is_lhs(true);
       op[0] = this->subexpressions[0]->hir(instructions, state);
       op[1] = this->subexpressions[1]->hir(instructions, state);
 
@@ -1640,6 +1661,7 @@ ast_expression::do_hir(exec_list *instructions,
 
    case ast_ls_assign:
    case ast_rs_assign: {
+      this->subexpressions[0]->set_is_lhs(true);
       op[0] = this->subexpressions[0]->hir(instructions, state);
       op[1] = this->subexpressions[1]->hir(instructions, state);
       type = shift_result_type(op[0]->type, op[1]->type, this->oper, state,
@@ -1658,6 +1680,7 @@ ast_expression::do_hir(exec_list *instructions,
    case ast_and_assign:
    case ast_xor_assign:
    case ast_or_assign: {
+      this->subexpressions[0]->set_is_lhs(true);
       op[0] = this->subexpressions[0]->hir(instructions, state);
       op[1] = this->subexpressions[1]->hir(instructions, state);
       type = bit_logic_result_type(op[0], op[1], this->oper, state, &loc);
@@ -1839,6 +1862,11 @@ ast_expression::do_hir(exec_list *instructions,
    case ast_array_index: {
       YYLTYPE index_loc = subexpressions[1]->get_location();
 
+      /* Getting if an array is being used uninitialized is beyond what we get
+       * from ir_value.data.assigned. Setting is_lhs as true would force to
+       * not raise a uninitialized warning when using an array
+       */
+      subexpressions[0]->set_is_lhs(true);
       op[0] = subexpressions[0]->hir(instructions, state);
       op[1] = subexpressions[1]->hir(instructions, state);
 
@@ -5746,6 +5774,11 @@ ast_switch_statement::test_to_hir(exec_list *instructions,
 {
    void *ctx = state;
 
+   /* set to true to avoid a duplicate "use of uninitialized variable" warning
+    * on the switch test case. The first one would be already raised when
+    * getting the test_expression at ast_switch_statement::hir
+    */
+   test_expression->set_is_lhs(true);
    /* Cache value of test expression. */
    ir_rvalue *const test_val =
       test_expression->hir(instructions,

src/compiler/glsl/glsl_parser_extras.cpp

@@ -1206,6 +1206,7 @@ ast_expression::ast_expression(int oper,
    this->subexpressions[1] = ex1;
    this->subexpressions[2] = ex2;
    this->non_lvalue_description = NULL;
+   this->is_lhs = false;
 }