From 2731a739d047e4aadc1cab4bcf8c01c1cf8e86db Mon Sep 17 00:00:00 2001 From: Eric Anholt Date: Wed, 23 Jun 2010 14:51:14 -0700 Subject: [PATCH] Avoid using the RHS of an assignment twice. This would fix double-evaluation of assignment RHS expressions, including possible side effects. --- ast_to_hir.cpp | 22 +++++++++++++++++++--- 1 file changed, 19 insertions(+), 3 deletions(-) diff --git a/ast_to_hir.cpp b/ast_to_hir.cpp index c059abbff6a..61e0d01a900 100644 --- a/ast_to_hir.cpp +++ b/ast_to_hir.cpp @@ -509,10 +509,26 @@ do_assignment(exec_list *instructions, struct _mesa_glsl_parse_state *state, } } - ir_instruction *tmp = new ir_assignment(lhs, rhs, NULL); - instructions->push_tail(tmp); + /* Most callers of do_assignment (assign, add_assign, pre_inc/dec, + * but not post_inc) need the converted assigned value as an rvalue + * to handle things like: + * + * i = j += 1; + * + * So we always just store the computed value being assigned to a + * temporary and return a deref of that temporary. If the rvalue + * ends up not being used, the temp will get copy-propagated out. + */ + ir_variable *var = new ir_variable(rhs->type, "assignment_tmp"); + instructions->push_tail(new ir_assignment(new ir_dereference_variable(var), + rhs, + NULL)); + + instructions->push_tail(new ir_assignment(lhs, + new ir_dereference_variable(var), + NULL)); - return rhs; + return new ir_dereference_variable(var); } -- 2.30.2