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ifcvt: Don't introduce trapping or faulting reads in noce_try_sign_mask [PR106032]

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noce_try_sign_mask as documented will optimize
  if (c < 0)
    x = t;
  else
    x = 0;
into x = (c >> bitsm1) & t;
The optimization is done if either t is unconditional
(e.g. for
  x = t;
  if (c >= 0)
    x = 0;
) or if it is cheap.  We already check that t doesn't have side-effects,
but if t is conditional, we need to punt also if it may trap or fault,
as we make it unconditional.

I've briefly skimmed other noce_try* optimizations and didn't find one that
would suffer from the same problem.

2022-06-21  Jakub Jelinek  <jakub@redhat.com>

	PR rtl-optimization/106032
	* ifcvt.cc (noce_try_sign_mask): Punt if !t_unconditional, and
	t may_trap_or_fault_p, even if it is cheap.

	* gcc.c-torture/execute/pr106032.c: New test.
This commit is contained in:
Jakub Jelinek 2022-06-21 11:40:16 +02:00
parent 2df1df945f
commit a0c30fe3b8
2 changed files with 29 additions and 7 deletions
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15
gcc/ifcvt.cc
View File

@ -2833,18 +2833,19 @@ noce_try_sign_mask (struct noce_if_info *if_info)
return FALSE;
/* This is only profitable if T is unconditionally executed/evaluated in the
original insn sequence or T is cheap. The former happens if B is the
non-zero (T) value and if INSN_B was taken from TEST_BB, or there was no
INSN_B which can happen for e.g. conditional stores to memory. For the
cost computation use the block TEST_BB where the evaluation will end up
after the transformation. */
original insn sequence or T is cheap and can't trap or fault. The former
happens if B is the non-zero (T) value and if INSN_B was taken from
TEST_BB, or there was no INSN_B which can happen for e.g. conditional
stores to memory. For the cost computation use the block TEST_BB where
the evaluation will end up after the transformation. */
t_unconditional
= (t == if_info->b
&& (if_info->insn_b == NULL_RTX
|| BLOCK_FOR_INSN (if_info->insn_b) == if_info->test_bb));
if (!(t_unconditional
|| (set_src_cost (t, mode, if_info->speed_p)
< COSTS_N_INSNS (2))))
|| ((set_src_cost (t, mode, if_info->speed_p)
< COSTS_N_INSNS (2))
&& !may_trap_or_fault_p (t))))
return FALSE;
if (!noce_can_force_operand (t))

21
gcc/testsuite/gcc.c-torture/execute/pr106032.c Normal file
View File

@ -0,0 +1,21 @@
/* PR rtl-optimization/106032 */
__attribute__((noipa)) int
foo (int x, int *y)
{
int a = 0;
if (x < 0)
a = *y;
return a;
}
int
main ()
{
int a = 42;
if (foo (0, 0) != 0 || foo (1, 0) != 0)
__builtin_abort ();
if (foo (-1, &a) != 42 || foo (-42, &a) != 42)
__builtin_abort ();
return 0;
}