On Wed, Aug 12, 2026 at 5:06 AM Andrea Pinski <[email protected]> wrote: > > A recent match patterns were added that introduce signed integer overflow > where > there was none before. `cmp + (-cmp ^ x)` has no signed integer overflow when > x is INT_MIN when cmp is 0. This gets translated into cmp ? -x : x. > But this has now introduced an signed integer overflow for INT_MIN. > The fix is to use unsigned type for the negative. > > Bootstrapped and tested on x86_64-linux-gnu.
OK. I've commented on 2/2 in v1. > Changes since v1: > * v2: Remove the abs patterns since a signed integer overflow would have > happened anyways. > > PR tree-optimization/126418 > > gcc/ChangeLog: > > * match.pd (`(A ^ -cmp) + cmp`): Cast to unsigned type > before taking the negative. > > gcc/testsuite/ChangeLog: > > * gcc.dg/tree-ssa/pr126418-1.c: New test. > > Signed-off-by: Andrea Pinski <[email protected]> > --- > gcc/match.pd | 8 +++++++- > gcc/testsuite/gcc.dg/tree-ssa/pr126418-1.c | 11 +++++++++++ > 2 files changed, 18 insertions(+), 1 deletion(-) > create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/pr126418-1.c > > diff --git a/gcc/match.pd b/gcc/match.pd > index 5da1e372f10..945fcabf956 100644 > --- a/gcc/match.pd > +++ b/gcc/match.pd > @@ -4942,7 +4942,13 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT) > (if (INTEGRAL_TYPE_P (type) > && !TYPE_SATURATING (type) > && (GIMPLE || !TREE_SIDE_EFFECTS (@0))) > - (cond (convert:boolean_type_node @1) (negate @0) @0))) > + /* Do the negate in unsigned type always; otherwise > + we would be introducing an overflow. */ > + (with { tree utype = unsigned_type_for (type); } > + (cond > + (convert:boolean_type_node @1) > + (convert:type (negate (convert:utype @0))) > + @0)))) > > /* Transform A & (B*cmp) into (A&B)*cmp. */ > (simplify > diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr126418-1.c > b/gcc/testsuite/gcc.dg/tree-ssa/pr126418-1.c > new file mode 100644 > index 00000000000..3714069b43f > --- /dev/null > +++ b/gcc/testsuite/gcc.dg/tree-ssa/pr126418-1.c > @@ -0,0 +1,11 @@ > +/* { dg-do compile } */ > +/* { dg-options "-O2 -fdump-tree-forwprop1" } */ > + > +int f_cmp_gt_commuted(int x, int y) > +{ > + int cmp = x > y; > + return cmp + (-cmp ^ x); > +} > + > +/* { dg-final { scan-tree-dump-times "\\(unsigned int\\) " 1 "forwprop1" } } > */ > +/* { dg-final { scan-tree-dump-times "\\(int\\) " 1 "forwprop1" } } */ > -- > 2.43.0 >
