GCC Middle and Back End API Reference
phiprop_d Struct Reference

Data Fields

tree value
tree vuse

Detailed Description


Backward propagation of indirect loads through PHIs. Copyright (C) 2007-2013 Free Software Foundation, Inc. Contributed by Richard Guenther rguen.nosp@m.ther.nosp@m.@suse.nosp@m..de

This file is part of GCC.

GCC is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 3, or (at your option) any later version.

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   This pass propagates indirect loads through the PHI node for its
   address to make the load source possibly non-addressable and to
   allow for PHI optimization to trigger.

   For example the pass changes

     # addr_1 = PHI <&a, &b>
     tmp_1 = *addr_1;


     # tmp_1 = PHI <a, b>

   but also handles more complex scenarios like

     D.2077_2 = &this_1(D)->a1;

     # b_12 = PHI <&c(2), D.2077_2(3)>
     D.2114_13 = *b_12;

     # b_15 = PHI <b_12(4), &b(5)>
     D.2080_5 = &this_1(D)->a0;

     # b_18 = PHI <D.2080_5(6), &c(7)>

     # b_21 = PHI <b_15(8), b_18(9)>
     D.2076_8 = *b_21;

   where the addresses loaded are defined by PHIs itself.
   The above happens for

     std::max(std::min(a0, c), std::min(std::max(a1, c), b))

   where this pass transforms it to a form later PHI optimization
   recognizes and transforms it to the simple

     D.2109_10 = this_1(D)->a1;
     D.2110_11 = c;
     D.2114_31 = MAX_EXPR <D.2109_10, D.2110_11>;
     D.2115_14 = b;
     D.2125_17 = MIN_EXPR <D.2115_14, D.2114_31>;
     D.2119_16 = this_1(D)->a0;
     D.2124_32 = MIN_EXPR <D.2110_11, D.2119_16>;
     D.2076_33 = MAX_EXPR <D.2125_17, D.2124_32>;

   The pass does a dominator walk processing loads using a basic-block
   local analysis and stores the result for use by transformations on
   dominated basic-blocks.  
   Structure to keep track of the value of a dereferenced PHI result
   and the virtual operand used for that dereference.  

Field Documentation

tree phiprop_d::value
tree phiprop_d::vuse

The documentation for this struct was generated from the following file: