Hi! If on &base->member the offset isn't constant or isn't zero and -fdelete-null-pointer-checks and not -fwrapv-pointer and base has a range that doesn't include NULL, we return the range of the base. Usually it isn't a big deal, because for most pointers we just use varying, range_zero and range_nonzero ranges and nothing beyond that, but if a pointer is initialized from a constant, we actually track the exact range and in that case this causes miscompilation. As discussed on IRC, I think doing something like: offset_int off2; if (off_cst && off.is_constant (&off2)) { tree cst = wide_int_to_tree (sizetype, off2 / BITS_PER_UNIT); // adjust range r with POINTER_PLUS_EXPR cst if (!range_includes_zero_p (&r)) return true; } // Fallback r = range_nonzero (TREE_TYPE (gimple_assign_rhs1 (stmt))); return true; could work, given that most of the pointer ranges are just the simple ones perhaps it is too much for little benefit.
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk? 2021-11-17 Jakub Jelinek <ja...@redhat.com> PR tree-optimization/103255 * gimple-range-fold.cc (fold_using_range::range_of_address): Return range_nonzero rather than unadjusted base's range. Formatting fixes. * gcc.c-torture/execute/pr103255.c: New test. --- gcc/gimple-range-fold.cc.jj 2021-11-04 12:27:02.341298923 +0100 +++ gcc/gimple-range-fold.cc 2021-11-16 22:10:44.453974329 +0100 @@ -720,14 +720,20 @@ fold_using_range::range_of_address (iran } /* If &X->a is equal to X, the range of X is the result. */ if (off_cst && known_eq (off, 0)) - return true; + return true; else if (flag_delete_null_pointer_checks && !TYPE_OVERFLOW_WRAPS (TREE_TYPE (expr))) { - /* For -fdelete-null-pointer-checks -fno-wrapv-pointer we don't - allow going from non-NULL pointer to NULL. */ - if(!range_includes_zero_p (&r)) - return true; + /* For -fdelete-null-pointer-checks -fno-wrapv-pointer we don't + allow going from non-NULL pointer to NULL. */ + if (!range_includes_zero_p (&r)) + { + /* We could here instead adjust r by off >> LOG2_BITS_PER_UNIT + using POINTER_PLUS_EXPR if off_cst and just fall back to + this. */ + r = range_nonzero (TREE_TYPE (gimple_assign_rhs1 (stmt))); + return true; + } } /* If MEM_REF has a "positive" offset, consider it non-NULL always, for -fdelete-null-pointer-checks also "negative" --- gcc/testsuite/gcc.c-torture/execute/pr103255.c.jj 2021-11-16 22:14:10.660118225 +0100 +++ gcc/testsuite/gcc.c-torture/execute/pr103255.c 2021-11-16 22:13:56.506314265 +0100 @@ -0,0 +1,41 @@ +/* PR tree-optimization/103255 */ + +struct H +{ + unsigned a; + unsigned b; + unsigned c; +}; + +#if __SIZEOF_POINTER__ >= 4 +#define ADDR 0x400000 +#else +#define ADDR 0x4000 +#endif +#define OFF 0x20 + +int +main () +{ + struct H *h = 0; + unsigned long o; + volatile int t = 1; + + for (o = OFF; o <= OFF; o += 0x1000) + { + struct H *u; + u = (struct H *) (ADDR + o); + if (t) + { + h = u; + break; + } + } + + if (h == 0) + return 0; + unsigned *tt = &h->b; + if ((__SIZE_TYPE__) tt != (ADDR + OFF + __builtin_offsetof (struct H, b))) + __builtin_abort (); + return 0; +} Jakub