On Sat, 26 Sep 2026, Andrea Pinski wrote: > On Sat, Sep 26, 2026 at 10:31 AM Dominic P <[email protected]> wrote: > > > > The ((X + C1) | (C2 - X)) < 0 fold from r17-4207 and its variants drop the > > C2 - X or -X operand, which traps on overflow under -ftrapv: for > > X = INT_MIN, ((X + 3) | -X) < 0 traps at -O0 but not at -O2. Do not > > match when overflow traps. The ABS_EXPR form from r17-4207 already > > requires TYPE_OVERFLOW_UNDEFINED. > > I am trying to remember the rules here but I think what this might be > doing is ok. -ftrapv and -fsanitize=undefined are fine to remove > traps with optimizations turned on. The only issue would be remove > the sanitization at -O0. > Note we should have this documented somewhere instead of these > undocumented rules too.
So for sanitizing we want to preserve original operations, but removing possible traps with -ftrapv was always considered OK - the point of TYPE_OVERFLOW_TRAPS checks should be to prevent new traps from being introduced where none were there before. That was also the stance for IEEE exceptions at some point (eliding them is OK, like via dead code removal). Richard. > Thanks, > Andrea > > > > > Bootstrapped and regression tested on x86_64-pc-linux-gnu. > > > > Assisted-by: Claude Opus 5 (Anthropic) > > > > gcc/ChangeLog: > > > > * match.pd (ior_range_test, ior_range_test_1, ior_range_test_0): > > Do not match if overflow traps. > > > > gcc/testsuite/ChangeLog: > > > > * gcc.dg/tree-ssa/ior-range-test-4.c: New test. > > > > Signed-off-by: Dominic P <[email protected]> > > --- > > OK for trunk? > > > > gcc/match.pd | 6 +++++- > > gcc/testsuite/gcc.dg/tree-ssa/ior-range-test-4.c | 14 ++++++++++++++ > > 2 files changed, 19 insertions(+), 1 deletion(-) > > create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/ior-range-test-4.c > > > > diff --git a/gcc/match.pd b/gcc/match.pd > > index 688357f0ecd..862da998e62 100644 > > --- a/gcc/match.pd > > +++ b/gcc/match.pd > > @@ -5164,22 +5164,26 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT) > > (bit_ior:c@3 (plus@0 @4 INTEGER_CST@1) (minus INTEGER_CST@2 @4)) > > (if (single_use (@3) > > && !TYPE_OVERFLOW_SANITIZED (TREE_TYPE (@0)) > > + && !TYPE_OVERFLOW_TRAPS (TREE_TYPE (@0)) > > && wi::ge_p (wi::to_wide (@1) + wi::to_wide (@2), 0, SIGNED)))) > > (match (ior_range_test_1 @0 @1) > > (bit_ior:c@2 @0 (minus INTEGER_CST@1 @0)) > > (if (single_use (@2) > > && !TYPE_OVERFLOW_SANITIZED (TREE_TYPE (@0)) > > + && !TYPE_OVERFLOW_TRAPS (TREE_TYPE (@0)) > > && wi::ge_p (wi::to_wide (@1), 0, SIGNED)))) > > (match (ior_range_test_1 @0 @1) > > (bit_ior:c@2 (plus@0 @3 INTEGER_CST@1) (negate @3)) > > (if (single_use (@2) > > && !TYPE_OVERFLOW_SANITIZED (TREE_TYPE (@0)) > > + && !TYPE_OVERFLOW_TRAPS (TREE_TYPE (@0)) > > && wi::ge_p (wi::to_wide (@1), 0, SIGNED)))) > > (match (ior_range_test_0 @0) > > (bit_ior:c@1 @0 (negate @0)) > > (if (INTEGRAL_TYPE_P (TREE_TYPE (@0)) > > && single_use (@1) > > - && !TYPE_OVERFLOW_SANITIZED (TREE_TYPE (@0))))) > > + && !TYPE_OVERFLOW_SANITIZED (TREE_TYPE (@0)) > > + && !TYPE_OVERFLOW_TRAPS (TREE_TYPE (@0))))) > > (for cmp (lt ge) > > out (gt le) > > (simplify > > diff --git a/gcc/testsuite/gcc.dg/tree-ssa/ior-range-test-4.c > > b/gcc/testsuite/gcc.dg/tree-ssa/ior-range-test-4.c > > new file mode 100644 > > index 00000000000..f9f0a1179b4 > > --- /dev/null > > +++ b/gcc/testsuite/gcc.dg/tree-ssa/ior-range-test-4.c > > @@ -0,0 +1,14 @@ > > +/* { dg-do compile } */ > > +/* { dg-options "-O2 -ftrapv -fdump-tree-optimized" } */ > > +/* { dg-require-effective-target int32 } */ > > + > > +/* The subtraction and the negation can trap. */ > > + > > +int f1 (int x) { return ((x + 1) | (1 - x)) < 0; } > > +int f2 (int x) { return (((x + 1) | (1 - x)) >> 31) & 1; } > > +int f3 (int x) { return (x | (6 - x)) < 0; } > > +int f4 (int x) { return ((x + 6) | -x) < 0; } > > +int f5 (int x) { return (x | -x) < 0; } > > +int f6 (int x) { return (unsigned) (x | -x) >> 31; } > > + > > +/* { dg-final { scan-tree-dump-times " \\| " 6 "optimized" } } */ > > -- > > 2.55.0 > > > -- Richard Biener <[email protected]> SUSE Software Solutions Germany GmbH, Frankenstrasse 146, 90461 Nuernberg, Germany; GF: Stefan Gaiser, Jochen Jaser, Abhinav Puri; (HRB 36809, AG Nuernberg)
