On Thu, Jul 06, 2023 at 03:00:28PM +0200, Richard Biener via Gcc-patches wrote:
> On Wed, Jul 5, 2023 at 3:42 PM Drew Ross via Gcc-patches
> <gcc-patches@gcc.gnu.org> wrote:
> >
> > Adds a simplification for (~X | Y) ^ X to be folded into ~(X & Y).
> > Tested successfully on x86_64 and x86 targets.
> >
> > PR middle-end/109986
> >
> > gcc/ChangeLog:
> >
> > * match.pd ((~X | Y) ^ X -> ~(X & Y)): New simplification.
> >
> > gcc/testsuite/ChangeLog:
> >
> > * gcc.c-torture/execute/pr109986.c: New test.
> > * gcc.dg/tree-ssa/pr109986.c: New test.
> > ---
> > gcc/match.pd | 11 ++
> > .../gcc.c-torture/execute/pr109986.c | 41 ++++
> > gcc/testsuite/gcc.dg/tree-ssa/pr109986.c | 177 ++++++++++++++++++
> > 3 files changed, 229 insertions(+)
> > create mode 100644 gcc/testsuite/gcc.c-torture/execute/pr109986.c
> > create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/pr109986.c
> >
> > diff --git a/gcc/match.pd b/gcc/match.pd
> > index a17d6838c14..d9d7d932881 100644
> > --- a/gcc/match.pd
> > +++ b/gcc/match.pd
> > @@ -1627,6 +1627,17 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
> > (if (tree_nop_conversion_p (type, TREE_TYPE (@0)))
> > (convert (bit_and @1 (bit_not @0)))))
> >
> > +/* (~X | Y) ^ X -> ~(X & Y). */
> > +(simplify
> > + (bit_xor:c (nop_convert1?
> > + (bit_ior:c (nop_convert2? (bit_not (nop_convert3? @0)))
> > + @1)) (nop_convert4? @0))
>
> you want to reduce the number of nop_convert? - for example
> I wonder if we can canonicalize
>
> (T)~X and ~(T)X
>
> for nop-conversions. The same might apply to binary bitwise operations
> where we should push those to a direction where they are likely eliminated.
> Usually we'd push them outwards.
>
> The issue with the above pattern is that nop_convertN? expands to 2^N
> separate patterns. Together with the two :c you get 64 out of this.
>
> I do not see that all of the combinations can happen when X has to
> match unless we fail to contract some of them like if we have
> (unsigned)(~(signed)X | Y) ^ X which we could rewrite like
> -> (unsigned)((signed)~X | Y) ^ X -> (~X | (unsigned) Y) ^ X
> with the last step being somewhat difficult unless we do
> (signed)~X | Y -> (signed)(~X | (unsigned)Y). It feels like a
> propagation problem and less of a direct pattern matching one.
The nop_convert1? in the pattern might seem to be unnecessary
for cases like:
int i, j, k, l;
unsigned u, v, w, x;
void
foo (void)
{
int t0 = i;
int t1 = (~t0) | j;
x = t1 ^ (unsigned) t0;
unsigned t2 = u;
unsigned t3 = (~t2) | v;
i = ((int) t3) ^ (int) t2;
}
we actually optimize it with or without the nop_convert1? in place,
because we have the
/* Try to fold (type) X op CST -> (type) (X op ((type-x) CST))
when profitable.
...
(bitop (convert@2 @0) (convert?@3 @1))
...
(convert (bitop @0 (convert @1)))))
simplification.
Except that on
void
bar (void)
{
unsigned t0 = u;
int t1 = (~(int) t0) | j;
x = t1 ^ t0;
int t2 = i;
unsigned t3 = (~(unsigned) t2) | v;
i = ((int) t3) ^ t2;
}
the optimization doesn't trigger without the nop_convert1? and does
with it.
Perhaps we could get rid of nop_convert3? and nop_convert4?
by introducing a macro/inline function predicate like:
bitwise_equal_p (expr1, expr2) and instead of using
(nop_convert3? @0) and (nop_convert4? @0) in the pattern
use @0 and @2 and then add
if (bitwise_equal_p (@0, @2))
to the condition.
For GENERIC (i.e. in generic-match-head.cc) it could be something like:
static inline bool
bitwise_equal_p (tree expr1, tree expr2)
{
STRIP_NOPS (expr1);
STRIP_NOPS (expr2);
if (expr1 == expr2)
return true;
if (!tree_nop_conversion_p (TREE_TYPE (expr1), TREE_TYPE (expr2)))
return false;
if (TREE_CODE (expr1) == INTEGER_CST && TREE_CODE (expr2) == INTEGER_CST)
return wi::to_wide (expr1) == wi::to_wide (expr2);
return operand_equal_p (expr1, expr2, 0);
}
(the INTEGER_CST special case because operand_equal_p compares wi::to_widest
which could be different if one constant is signed and the other unsigned).
For GIMPLE, I wonder if it shouldn't be a macro that takes valueize into
account, and do something like:
#define bitwise_equal_p(expr1, expr2) gimple_bitwise_equal_p (expr1, expr2,
valueize)
bool gimple_nop_convert (tree, tree *, tree (*)(tree));
static inline bool
gimple_bitwise_equal_p (tree expr1, tree expr2, tree (*valueize) (tree))
{
if (expr1 == expr2)
return true;
if (!tree_nop_conversion_p (TREE_TYPE (expr1), TREE_TYPE (expr2)))
return false;
if (TREE_CODE (expr1) == INTEGER_CST && TREE_CODE (expr2) == INTEGER_CST)
return wi::to_wide (expr1) == wi::to_wide (expr2);
if (operand_equal_p (expr1, expr2, 0))
return true;
tree expr3, expr4;
if (!gimple_nop_convert (expr1, &expr3, valueize))
expr3 = expr1;
if (!gimple_nop_convert (expr2, &expr4, valueize))
expr4 = expr2;
if (expr1 != expr3)
{
if (operand_equal_p (expr3, expr2, 0))
return true;
if (expr2 != expr4 && operand_equal_p (expr3, expr4, 0))
return true;
}
if (expr2 != expr4 && operand_equal_p (expr1, expr4, 0))
return true;
return false;
}
Completely untested. What do you think?
Though, that brings us only still to 16 cases of this.
Jakub
