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sccvn: Fix visit_reference_op_call value numbering of vdefs [PR104601]

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The following testcase is miscompiled, because -fipa-pure-const discovers
that bar is const, but when sccvn during fre3 sees
  # .MEM_140 = VDEF <.MEM_96>
  *__pred$__d_43 = _50 (_49);
where _50 value numbers to &bar, it value numbers .MEM_140 to
vuse_ssa_val (gimple_vuse (stmt)).  For const/pure calls that return
a SSA_NAME (or don't have lhs) that is fine, those calls don't store
anything, but if the lhs is present and not an SSA_NAME, value numbering
the vdef to anything but itself means that e.g. walk_non_aliased_vuses
won't consider the call, but the call acts as a store to its lhs.
When it is ignored, sccvn will return whatever has been stored to the
lhs earlier.

I've bootstrapped/regtested an earlier version of this patch, which did the
if (!lhs && gimple_call_lhs (stmt))
  changed |= set_ssa_val_to (vdef, vdef);
part before else if (vnresult->result_vdef), and that regressed
+FAIL: gcc.dg/pr51879-16.c scan-tree-dump-times pre "foo \\\\(" 1
+FAIL: gcc.dg/pr51879-16.c scan-tree-dump-times pre "foo2 \\\\(" 1
so this updated patch uses result_vdef there as before and only otherwise
(which I think must be the const/pure case) decides based on whether the
lhs is non-SSA_NAME.

2022-02-24  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/104601
	* tree-ssa-sccvn.cc (visit_reference_op_call): For calls with
	non-SSA_NAME lhs value number vdef to itself instead of e.g. the
	vuse value number.

	* g++.dg/torture/pr104601.C: New test.
This commit is contained in:
Jakub Jelinek 2022-02-24 15:29:02 +01:00
parent 59b8ade887
commit 9251b457eb
2 changed files with 51 additions and 7 deletions
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32
gcc/testsuite/g++.dg/torture/pr104601.C Normal file
View file

@ -0,0 +1,32 @@
// PR tree-optimization/104601
// { dg-do run }
// { dg-options "-std=c++17" }
#include <algorithm>
#include <optional>
inline std::optional<int>
foo (std::vector<int>::iterator b, std::vector<int>::iterator c,
std::optional<int> h (int))
{
std::optional<int> d;
find_if (b, c, [&](auto e) { d = h(e); return d; });
return d;
}
std::optional<int>
bar (int)
{
return 1;
}
int
main ()
{
std::vector<int> g(10);
auto b = g.begin ();
auto c = g.end ();
auto e = foo (b, c, bar);
if (!e)
__builtin_abort ();
}

26
gcc/tree-ssa-sccvn.cc
View file

@ -5218,12 +5218,20 @@ visit_reference_op_call (tree lhs, gcall *stmt)
if (vnresult)
{
if (vnresult->result_vdef && vdef)
changed |= set_ssa_val_to (vdef, vnresult->result_vdef);
else if (vdef)
/* If the call was discovered to be pure or const reflect
that as far as possible. */
changed |= set_ssa_val_to (vdef, vuse_ssa_val (gimple_vuse (stmt)));
if (vdef)
{
if (vnresult->result_vdef)
changed |= set_ssa_val_to (vdef, vnresult->result_vdef);
else if (!lhs && gimple_call_lhs (stmt))
/* If stmt has non-SSA_NAME lhs, value number the vdef to itself,
as the call still acts as a lhs store. */
changed |= set_ssa_val_to (vdef, vdef);
else
/* If the call was discovered to be pure or const reflect
that as far as possible. */
changed |= set_ssa_val_to (vdef,
vuse_ssa_val (gimple_vuse (stmt)));
}
if (!vnresult->result && lhs)
vnresult->result = lhs;
@ -5248,7 +5256,11 @@ visit_reference_op_call (tree lhs, gcall *stmt)
if (TREE_CODE (fn) == ADDR_EXPR
&& TREE_CODE (TREE_OPERAND (fn, 0)) == FUNCTION_DECL
&& (flags_from_decl_or_type (TREE_OPERAND (fn, 0))
& (ECF_CONST | ECF_PURE)))
& (ECF_CONST | ECF_PURE))
/* If stmt has non-SSA_NAME lhs, value number the
vdef to itself, as the call still acts as a lhs
store. */
&& (lhs || gimple_call_lhs (stmt) == NULL_TREE))
vdef_val = vuse_ssa_val (gimple_vuse (stmt));
}
changed |= set_ssa_val_to (vdef, vdef_val);