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reassoc: Fix up (ab) handling in eliminate_redundant_comparison [PR108783]

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The following testcase ICEs because eliminate_redundant_comparison sees
redundant comparisons in &&/|| where the comparison has (ab) SSA_NAME,
maybe_fold_{and,or}_comparisons optimizes them into a single comparison
and build_and_add_sum emits a new comparison close to the definition
operands, which in this case is before a returns_twice call (which is
invalid).  Generally reassoc just punts on (ab) SSA_NAMEs, declares them
non-reassociable etc., so the second half of this patch does that.

Though we can do better in this case; the function has special code
when maybe_fold_{and,or}_comparisons returns INTEGER_CST (false/true)
or when what it returns is the same as curr->op (the first of the
comparisons we are considering) - in that case we just remove the
second one and keep the first one.  The reason it doesn't match is that
curr->op is a SSA_NAME whose SSA_NAME_DEF_STMT is checked to be a
comparison, in this case _42 = a_1(ab) != 0 and the other comparison
is also like that.  maybe_fold_{and,or}_comparisons looks through the
definitions though and so returns a_1(ab) != 0 as tree.
So the first part of the patch checks whether that returned comparison
isn't the same as the curr->op comparison and if yes, it just overrides
t back to curr->op so that its SSA_NAME is reused.  In that case we can
handle even (ab) in {,new}op{1,2} because we don't create a new comparison
of that, just keep using the existing one.  And t can't be (ab) because
otherwise it wouldn't be considered a reassociable operand.

The (ab) checks are needed say when we have a_1(ab) == 42 || a_1(ab) > 42
kind of comparisons where maybe_fold_{and,or}_comparisons returns a new
comparison not existing in the IL yet.

2023-02-16  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/108783
	* tree-ssa-reassoc.cc (eliminate_redundant_comparison): If lcode
	is equal to TREE_CODE (t), op1 to newop1 and op2 to newop2, set
	t to curr->op.  Otherwise, punt if either newop1 or newop2 are
	SSA_NAME_OCCURS_IN_ABNORMAL_PHI SSA_NAMEs.

	* gcc.c-torture/compile/pr108783.c: New test.
This commit is contained in:
Jakub Jelinek 2023-02-16 10:41:18 +01:00
parent 441c466fd4
commit 55db240d28
2 changed files with 51 additions and 0 deletions
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42
gcc/testsuite/gcc.c-torture/compile/pr108783.c Normal file
View file

@ -0,0 +1,42 @@
/* PR tree-optimization/108783 */
__attribute__((returns_twice)) int baz (int, int);
int
bar (int x)
{
return x;
}
int
foo (int x, int y)
{
int a;
a = bar (x);
baz (x, y);
return y && a && a;
}
int
qux (int x, int y)
{
int a;
a = bar (x);
baz (x, y);
return y && a != 42 && a >= 42;
}
int
corge (int x, int y)
{
int a;
a = bar (x);
baz (x, y);
return y || a == 42 || a > 42;
}

9
gcc/tree-ssa-reassoc.cc
View file

@ -2272,6 +2272,15 @@ eliminate_redundant_comparison (enum tree_code opcode,
STRIP_USELESS_TYPE_CONVERSION (newop2);
if (!is_gimple_val (newop1) || !is_gimple_val (newop2))
continue;
if (lcode == TREE_CODE (t)
&& operand_equal_p (op1, newop1, 0)
&& operand_equal_p (op2, newop2, 0))
t = curr->op;
else if ((TREE_CODE (newop1) == SSA_NAME
&& SSA_NAME_OCCURS_IN_ABNORMAL_PHI (newop1))
|| (TREE_CODE (newop2) == SSA_NAME
&& SSA_NAME_OCCURS_IN_ABNORMAL_PHI (newop2)))
continue;
}
if (dump_file && (dump_flags & TDF_DETAILS))