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irange: keep better track of powers of 2.

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When setting the nonzero bits to a mask containing only one bit, set
the range immediately, as it can be devined from the mask.  This helps
us keep better track of powers of two.

For example, with this patch a nonzero mask of 0x8000 is set to a
range of [0,0][0x8000,0x8000] with a nonzero mask of 0x8000.

gcc/ChangeLog:

	* value-range.cc (irange::set_nonzero_bits): Set range when known.

gcc/testsuite/ChangeLog:

	* gcc.dg/tree-ssa/popcount6.c: New test.
This commit is contained in:
Aldy Hernandez 2022-09-27 08:05:30 +02:00
parent 1db05e1a1c
commit be4a6551ed
2 changed files with 25 additions and 0 deletions
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12
gcc/testsuite/gcc.dg/tree-ssa/popcount6.c Normal file
View file

@ -0,0 +1,12 @@
// { dg-do compile }
// { dg-options "-O2 -fdump-tree-evrp" }
int g(int n)
{
n &= 0x8000;
if (n == 0)
return 1;
return __builtin_popcount(n);
}
// { dg-final { scan-tree-dump "return 1;" "evrp" } }

13
gcc/value-range.cc
View file

@ -2930,6 +2930,19 @@ irange::set_nonzero_bits (const wide_int_ref &bits)
set_nonzero_bits (NULL);
return;
}
// If we have only one bit set in the mask, we can figure out the
// range immediately.
if (wi::popcount (bits) == 1)
{
bool has_zero = contains_p (build_zero_cst (type ()));
set (type (), bits, bits);
if (has_zero)
{
int_range<2> zero;
zero.set_zero (type ());
union_ (zero);
}
}
set_nonzero_bits (wide_int_to_tree (type (), bits));
}