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) 2007-2024 Free Software Foundation, Inc.
   Contributed by Richard Guenther <rguenther@suse.de>

This file is part of GCC.

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it under the terms of the GNU General Public License as published by
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GCC is distributed in the hope that it will be useful,
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You should have received a copy of the GNU General Public License
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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

◆ value

tree phiprop_d::value

◆ vuse

tree phiprop_d::vuse

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