On Thu, Jun 16, 2011 at 5:24 PM, Zdenek Dvorak <rakd...@kam.mff.cuni.cz> wrote: > Hi, > >> diff -u gcc/tree-ssa-loop-niter.c (working copy) gcc/tree-ssa-loop-niter.c >> (working copy) >> --- gcc/tree-ssa-loop-niter.c (working copy) >> +++ gcc/tree-ssa-loop-niter.c (working copy) >> @@ -2875,6 +2875,16 @@ >> low = lower_bound_in_type (type, type); >> high = upper_bound_in_type (type, type); >> >> + /* In C, pointer arithmetic p + 1 cannot use a NULL pointer, and p - 1 >> cannot >> + produce a NULL pointer. The contrary would mean NULL points to an >> object, >> + while NULL is supposed to compare unequal with the address of all >> objects. >> + Furthermore, p + 1 cannot produce a NULL pointer and p - 1 cannot use a >> + NULL pointer since that would mean wrapping, which we assume here not >> to >> + happen. So, we can exclude NULL from the valid range of pointer >> + arithmetic. */ >> + if (int_cst_value (low) == 0) >> + low = build_int_cstu (TREE_TYPE (low), TYPE_ALIGN_UNIT (TREE_TYPE >> (type))); >> + >> record_nonwrapping_iv (loop, base, step, stmt, low, high, false, true); >> } > > OK,
I think this is only valid for !flag_delete_null_pointer_checks, on architectures where that isn't the default we have to assume that NULL may point to an object. Richard. > Zdenek >
