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path oracle: Do not look at root oracle for killed defs.

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The problem here is that we are incorrectly threading 41->20->21 here:

  <bb 35> [local count: 56063504182]:
  _134 = M.10_120 + 1;
  if (_71 <= _134)
    goto <bb 19>; [11.00%]
  else
    goto <bb 41>; [89.00%]
...
...
...
  <bb 41> [local count: 49896518755]:

  <bb 20> [local count: 56063503181]:
  # lb_75 = PHI <_134(41), 1(18)>
  _117 = mstep_49 + lb_75;
  _118 = _117 + -1;
  _119 = mstep_49 + _118;
  M.10_120 = MIN_EXPR <_119, _71>;
  if (lb_75 > M.10_120)
    goto <bb 21>; [11.00%]
  else
    goto <bb 22>; [89.00%]

First, lb_17 == _134 because of the PHI.
Second, _134 > M.10_120 because of _134 = M.10_120 + 1.

We then assume that lb_75 > M.10_120, but this is incorrect because
M.10_120 was killed along the path.

This incorrect thread causes the miscompilation in 527.cam4_r.

Tested on x86-64 and ppc64le Linux.

gcc/ChangeLog:

	PR tree-optimization/103061
	* value-relation.cc (path_oracle::path_oracle): Initialize
	m_killed_defs.
	(path_oracle::killing_def): Set m_killed_defs.
	(path_oracle::query_relation): Do not look at the root oracle for
	killed defs.
	* value-relation.h (class path_oracle): Add m_killed_defs.
This commit is contained in:
Aldy Hernandez 2021-11-05 22:25:19 +01:00
parent b3a38d1835
commit 4856699eeb
2 changed files with 10 additions and 0 deletions
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9
gcc/value-relation.cc
View file

@ -1235,6 +1235,7 @@ path_oracle::path_oracle (relation_oracle *oracle)
m_equiv.m_next = NULL;
m_relations.m_names = BITMAP_ALLOC (&m_bitmaps);
m_relations.m_head = NULL;
m_killed_defs = BITMAP_ALLOC (&m_bitmaps);
}
path_oracle::~path_oracle ()
@ -1305,6 +1306,8 @@ path_oracle::killing_def (tree ssa)
unsigned v = SSA_NAME_VERSION (ssa);
bitmap_set_bit (m_killed_defs, v);
// Walk the equivalency list and remove SSA from any equivalencies.
if (bitmap_bit_p (m_equiv.m_names, v))
{
@ -1389,6 +1392,12 @@ path_oracle::query_relation (basic_block bb, const_bitmap b1, const_bitmap b2)
relation_kind k = m_relations.find_relation (b1, b2);
// Do not look at the root oracle for names that have been killed
// along the path.
if (bitmap_intersect_p (m_killed_defs, b1)
|| bitmap_intersect_p (m_killed_defs, b2))
return k;
if (k == VREL_NONE && m_root)
k = m_root->query_relation (bb, b1, b2);

1
gcc/value-relation.h
View file

@ -233,6 +233,7 @@ private:
equiv_chain m_equiv;
relation_chain_head m_relations;
relation_oracle *m_root;
bitmap m_killed_defs;
bitmap_obstack m_bitmaps;
struct obstack m_chain_obstack;