diff options
| -rw-r--r-- | src/glsl/ast_to_hir.cpp | 36 |
1 files changed, 35 insertions, 1 deletions
diff --git a/src/glsl/ast_to_hir.cpp b/src/glsl/ast_to_hir.cpp index a11bfbab887..18e66db2e2a 100644 --- a/src/glsl/ast_to_hir.cpp +++ b/src/glsl/ast_to_hir.cpp @@ -1664,8 +1664,42 @@ ast_expression::hir(exec_list *instructions, * therefore add instructions to the instruction list), they get dropped * on the floor. */ - foreach_list_typed (ast_node, ast, link, &this->expressions) + exec_node *previous_tail_pred = NULL; + YYLTYPE previous_operand_loc = loc; + + foreach_list_typed (ast_node, ast, link, &this->expressions) { + /* If one of the operands of comma operator does not generate any + * code, we want to emit a warning. At each pass through the loop + * previous_tail_pred will point to the last instruction in the + * stream *before* processing the previous operand. Naturally, + * instructions->tail_pred will point to the last instruction in the + * stream *after* processing the previous operand. If the two + * pointers match, then the previous operand had no effect. + * + * The warning behavior here differs slightly from GCC. GCC will + * only emit a warning if none of the left-hand operands have an + * effect. However, it will emit a warning for each. I believe that + * there are some cases in C (especially with GCC extensions) where + * it is useful to have an intermediate step in a sequence have no + * effect, but I don't think these cases exist in GLSL. Either way, + * it would be a giant hassle to replicate that behavior. + */ + if (previous_tail_pred == instructions->tail_pred) { + _mesa_glsl_warning(&previous_operand_loc, state, + "left-hand operand of comma expression has " + "no effect"); + } + + /* tail_pred is directly accessed instead of using the get_tail() + * method for performance reasons. get_tail() has extra code to + * return NULL when the list is empty. We don't care about that + * here, so using tail_pred directly is fine. + */ + previous_tail_pred = instructions->tail_pred; + previous_operand_loc = ast->get_location(); + result = ast->hir(instructions, state); + } type = result->type; |