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      1 /*
      2  * Copyright  2013 Intel Corporation
      3  *
      4  * Permission is hereby granted, free of charge, to any person obtaining a
      5  * copy of this software and associated documentation files (the "Software"),
      6  * to deal in the Software without restriction, including without limitation
      7  * the rights to use, copy, modify, merge, publish, distribute, sublicense,
      8  * and/or sell copies of the Software, and to permit persons to whom the
      9  * Software is furnished to do so, subject to the following conditions:
     10  *
     11  * The above copyright notice and this permission notice (including the next
     12  * paragraph) shall be included in all copies or substantial portions of the
     13  * Software.
     14  *
     15  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
     16  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
     17  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
     18  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
     19  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
     20  * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
     21  * DEALINGS IN THE SOFTWARE.
     22  */
     23 
     24 /**
     25  * \file opt_flatten_nested_if_blocks.cpp
     26  *
     27  * Flattens nested if blocks such as:
     28  *
     29  * if (x) {
     30  *    if (y) {
     31  *       ...
     32  *    }
     33  * }
     34  *
     35  * into a single if block with a combined condition:
     36  *
     37  * if (x && y) {
     38  *    ...
     39  * }
     40  */
     41 
     42 #include "ir.h"
     43 #include "ir_builder.h"
     44 
     45 using namespace ir_builder;
     46 
     47 namespace {
     48 
     49 class nested_if_flattener : public ir_hierarchical_visitor {
     50 public:
     51    nested_if_flattener()
     52    {
     53       progress = false;
     54    }
     55 
     56    ir_visitor_status visit_leave(ir_if *);
     57    ir_visitor_status visit_enter(ir_assignment *);
     58 
     59    bool progress;
     60 };
     61 
     62 } /* unnamed namespace */
     63 
     64 /* We only care about the top level "if" instructions, so don't
     65  * descend into expressions.
     66  */
     67 ir_visitor_status
     68 nested_if_flattener::visit_enter(ir_assignment *ir)
     69 {
     70    (void) ir;
     71    return visit_continue_with_parent;
     72 }
     73 
     74 bool
     75 opt_flatten_nested_if_blocks(exec_list *instructions)
     76 {
     77    nested_if_flattener v;
     78 
     79    v.run(instructions);
     80    return v.progress;
     81 }
     82 
     83 
     84 ir_visitor_status
     85 nested_if_flattener::visit_leave(ir_if *ir)
     86 {
     87    /* Only handle a single ir_if within the then clause of an ir_if.  No extra
     88     * instructions, no else clauses, nothing.
     89     */
     90    if (ir->then_instructions.is_empty() || !ir->else_instructions.is_empty())
     91       return visit_continue;
     92 
     93    ir_if *inner = ((ir_instruction *) ir->then_instructions.get_head_raw())->as_if();
     94    if (!inner || !inner->next->is_tail_sentinel() ||
     95        !inner->else_instructions.is_empty())
     96       return visit_continue;
     97 
     98    ir->condition = logic_and(ir->condition, inner->condition);
     99    inner->then_instructions.move_nodes_to(&ir->then_instructions);
    100 
    101    progress = true;
    102    return visit_continue;
    103 }
    104