On Fri, Aug 14, 2026 at 8:21 AM Andrea Pinski <[email protected]> wrote: > > This adds some extra checks to see if we can remove the casts > for signed integer overflow reasons while doing a negative. > This is needed more due to the recent patch which adds them > in some cases. > > This also changes TYPE_UNSIGNED to be TYPE_OVERFLOW_WRAPS to > allow this to happen with -fwrapv too. > > Changes since v1: > * Use expr_not_equal_to and simplify the if stmt. > Also use TYPE_OVERFLOW_WRAPS instead of TYPE_UNSIGNED. > > Bootstrapped and tested on x86_64-linux-gnu.
OK. > PR tree-optimization/107765 > > gcc/ChangeLog: > > * match.pd (`(cast)-(cast)a`): Expand to > use expr_not_equal_to of INT_MIN. > > gcc/testsuite/ChangeLog: > > * gcc.dg/tree-ssa/neg-cast-1.c: New test. > * gcc.dg/tree-ssa/neg-cast-4.c: New test. > > Signed-off-by: Andrea Pinski <[email protected]> > --- > gcc/match.pd | 10 +++++++--- > gcc/testsuite/gcc.dg/tree-ssa/neg-cast-1.c | 23 ++++++++++++++++++++++ > gcc/testsuite/gcc.dg/tree-ssa/neg-cast-4.c | 16 +++++++++++++++ > 3 files changed, 46 insertions(+), 3 deletions(-) > create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/neg-cast-1.c > create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/neg-cast-4.c > > diff --git a/gcc/match.pd b/gcc/match.pd > index 4631e811108..30657fa5bae 100644 > --- a/gcc/match.pd > +++ b/gcc/match.pd > @@ -1231,13 +1231,17 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT) > show up. Else it is safe if the negation is done in an unsigned type. > Note the outer cast cannot be a boolean type as the only valid values > are 0,-1/1 (depending on the signedness of the boolean) and the negative > - is there to get the correct value. */ > + is there to get the correct value. > + Also handle the case where we know that we won't cause a signed > + integer overflow at the point of the negation. */ > (simplify > - (convert (negate:s@1 (convert:s @0))) > + (convert (negate:s@1 (convert:s@ic @0))) > (if (INTEGRAL_TYPE_P (type) > && tree_nop_conversion_p (type, TREE_TYPE (@1)) > && (TYPE_PRECISION (type) > TYPE_PRECISION (TREE_TYPE (@0)) > - || TYPE_UNSIGNED (type)) > + || TYPE_OVERFLOW_WRAPS (type) > + || expr_not_equal_to (@ic, wi::min_value (signed_type_for (type)), > + gimple_match_ctx (@1))) > && TREE_CODE (type) != BOOLEAN_TYPE) > (negate (convert @0)))) > > diff --git a/gcc/testsuite/gcc.dg/tree-ssa/neg-cast-1.c > b/gcc/testsuite/gcc.dg/tree-ssa/neg-cast-1.c > new file mode 100644 > index 00000000000..ec5d0e15251 > --- /dev/null > +++ b/gcc/testsuite/gcc.dg/tree-ssa/neg-cast-1.c > @@ -0,0 +1,23 @@ > +/* { dg-do compile } */ > +/* { dg-options "-O2 -fdump-tree-optimized -fdump-tree-cddce1" } */ > +/* PR tree-optimization/107765 */ > + > +int a(int input) > +{ > + if (input == -__INT_MAX__-1) return 1; > + unsigned t = input; > + int tt = -t; > + return tt == -input; > +} > + > +int b(int input) > +{ > + if (input == -__INT_MAX__-1) __builtin_trap(); > + unsigned t = input; > + int tt = -t; > + return tt; > +} > + > +/* { dg-final { scan-tree-dump "return 1" "optimized" } } */ > +/* { dg-final { scan-tree-dump-not "\\(unsigned int\\)" "cddce1" } } */ > +/* { dg-final { scan-tree-dump-not "\\(int\\)" "cddce1" } } */ > diff --git a/gcc/testsuite/gcc.dg/tree-ssa/neg-cast-4.c > b/gcc/testsuite/gcc.dg/tree-ssa/neg-cast-4.c > new file mode 100644 > index 00000000000..fe3fe6a2ecc > --- /dev/null > +++ b/gcc/testsuite/gcc.dg/tree-ssa/neg-cast-4.c > @@ -0,0 +1,16 @@ > +/* { dg-do compile } */ > +/* { dg-options "-O2 -fdump-tree-phiopt2-details -fdump-tree-optimized" } */ > +/* PR tree-optimization/107765 */ > + > +int b(int input) > +{ > + if (input == -__INT_MAX__-1) return input; > + unsigned t = input; > + int tt = -t; > + return tt; > +} > + > +/* { dg-final { scan-tree-dump-not "if " "optimized" } } */ > +/* { dg-final { scan-tree-dump-times "\\(unsigned int\\)" 1 "optimized" } } > */ > +/* { dg-final { scan-tree-dump-times "\\(int\\)" 1 "optimized" } } */ > +/* { dg-final { scan-tree-dump-times "converted to straightline code" 1 > "phiopt2" } } */ > -- > 2.43.0 >
