On Mon, Jul 21, 2025 at 12:07 AM Richard Biener <richard.guent...@gmail.com> wrote: > > On Mon, Jul 21, 2025 at 1:30 AM Andrew Pinski <quic_apin...@quicinc.com> > wrote: > > > > I have seen this a few places though the testcase from PR 95906 > > is an obvious place where this shows up for sure. > > This convert `cmp - 1` into `-icmp` as that form is more useful > > in many cases. > > > > Bootstrapped and tested on x86_64-linux-gnu. > > I think we want to ensure that TYPE_PRECISION (type) > 1 > (considering a cast from unsigned bool to signed and thus UB > for -1 + -1). > > OK with that change.
This is what I pushed in the end.
Thanks,
Andrew
>
> Thanks,
> Richard.
>
> > PR tree-optimization/110949
> > PR tree-optimization/95906
> >
> > gcc/ChangeLog:
> >
> > * match.pd (cmp - 1): New pattern.
> >
> > gcc/testsuite/ChangeLog:
> >
> > * gcc.dg/tree-ssa/cmp-2.c: New test.
> > * gcc.dg/tree-ssa/max-bitcmp-1.c: New test.
> >
> > Signed-off-by: Andrew Pinski <quic_apin...@quicinc.com>
> > ---
> > gcc/match.pd | 17 ++++++++++++++++-
> > gcc/testsuite/gcc.dg/tree-ssa/cmp-2.c | 14 ++++++++++++++
> > gcc/testsuite/gcc.dg/tree-ssa/max-bitcmp-1.c | 19 +++++++++++++++++++
> > 3 files changed, 49 insertions(+), 1 deletion(-)
> > create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/cmp-2.c
> > create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/max-bitcmp-1.c
> >
> > diff --git a/gcc/match.pd b/gcc/match.pd
> > index 7f84d5149f4..3e8b324e376 100644
> > --- a/gcc/match.pd
> > +++ b/gcc/match.pd
> > @@ -7035,6 +7035,21 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
> > (icmp @0 @1)
> > (if (ic == ncmp)
> > (ncmp @0 @1)))))
> > + /* ((cast)cmp) - 1 -> -(cast)icmp . */
> > + (simplify
> > + (plus (convert? (cmp@2 @0 @1)) integer_minus_onep)
> > + (if (INTEGRAL_TYPE_P (TREE_TYPE (@2)) && TYPE_PRECISION (TREE_TYPE
> > (@2)) == 1)
> > + /* Comparison inversion may be impossible for trapping math,
> > + invert_tree_comparison will tell us. But we can't use
> > + a computed operator in the replacement tree thus we have
> > + to play the trick below. */
> > + (with { enum tree_code ic = invert_tree_comparison
> > + (cmp, HONOR_NANS (@0));
> > + tree cmptype = TREE_TYPE (@2); }
> > + (if (ic == icmp)
> > + (negate (convert (icmp:cmptype @0 @1)))
> > + (if (ic == ncmp)
> > + (negate (convert (ncmp:cmptype @0 @1))))))))
> > /* The following bits are handled by fold_binary_op_with_conditional_arg.
> > */
> > (simplify
> > (ne (cmp@2 @0 @1) integer_zerop)
> > @@ -11678,4 +11693,4 @@ and,
> > && VECTOR_TYPE_P (type)
> > && direct_internal_fn_supported_p (IFN_AVG_CEIL, type,
> > OPTIMIZE_FOR_BOTH))
> > (IFN_AVG_CEIL @0 @2)))
> > -#endif
> > \ No newline at end of file
> > +#endif
> > diff --git a/gcc/testsuite/gcc.dg/tree-ssa/cmp-2.c
> > b/gcc/testsuite/gcc.dg/tree-ssa/cmp-2.c
> > new file mode 100644
> > index 00000000000..9b029019c06
> > --- /dev/null
> > +++ b/gcc/testsuite/gcc.dg/tree-ssa/cmp-2.c
> > @@ -0,0 +1,14 @@
> > +/* { dg-do compile } */
> > +/* { dg-options "-O1 -fdump-tree-forwprop" } */
> > +
> > +/* PR tree-optimization/110949 */
> > +/* Transform `(cmp) - 1` into `-icmp`. */
> > +
> > +int f1(int a)
> > +{
> > + int t = a == 115;
> > + return t - 1;
> > +}
> > +
> > +/* { dg-final { scan-tree-dump " != 115" "forwprop1" } } */
> > +/* { dg-final { scan-tree-dump-not " == 115" "forwprop1" } } */
> > diff --git a/gcc/testsuite/gcc.dg/tree-ssa/max-bitcmp-1.c
> > b/gcc/testsuite/gcc.dg/tree-ssa/max-bitcmp-1.c
> > new file mode 100644
> > index 00000000000..81b5a27c045
> > --- /dev/null
> > +++ b/gcc/testsuite/gcc.dg/tree-ssa/max-bitcmp-1.c
> > @@ -0,0 +1,19 @@
> > +/* { dg-do compile } */
> > +/* { dg-options "-O1 -fdump-tree-forwprop -fdump-tree-optimized" } */
> > +
> > +/* PR tree-optimization/95906 */
> > +/* this should become MAX_EXPR<a,b> */
> > +
> > +int f2(int a, int b)
> > +{
> > + int cmp = -(a > b);
> > + return (cmp & a) | (~cmp & b);
> > +}
> > +
> > +/* we should not end up with -_2 */
> > +/* we should not end up and & nor a `+ -1` */
> > +/* In optimized we should have a max. */
> > +/* { dg-final { scan-tree-dump-not " -\[a-zA-Z_\]" "forwprop1" } } */
> > +/* { dg-final { scan-tree-dump-not " & " "forwprop1" } } */
> > +/* { dg-final { scan-tree-dump-not " . -1" "forwprop1" } } */
> > +/* { dg-final { scan-tree-dump-times "MAX_EXPR " 1 "optimized" } } */
> > --
> > 2.43.0
> >
0001-match-Add-cmp-1-simplification-to-icmp-PR110949.patch
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