https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97457
--- Comment #5 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The releases/gcc-10 branch has been updated by Richard Sandiford <rsand...@gcc.gnu.org>: https://gcc.gnu.org/g:75a5af680a1788ba844902fd0681958da8e2a4ce commit r10-9112-g75a5af680a1788ba844902fd0681958da8e2a4ce Author: Richard Sandiford <richard.sandif...@arm.com> Date: Wed Dec 2 18:39:24 2020 +0000 value-range: Give up on POLY_INT_CST ranges [PR97457] This PR shows another problem with calculating value ranges for POLY_INT_CSTs. We have: ivtmp_76 = ASSERT_EXPR <ivtmp_60, ivtmp_60 > POLY_INT_CST [9, 4294967294]> where the VQ coefficient is unsigned but is effectively acting as a negative number. We wrongly give the POLY_INT_CST the range: [9, INT_MAX] and things go downhill from there: later iterations of the unrolled epilogue are wrongly removed as dead. I guess this is the final nail in the coffin for doing VRP on POLY_INT_CSTs. For other similarly exotic testcases we could have overflow for any coefficient, not just those that could be treated as contextually negative. Testing TYPE_OVERFLOW_UNDEFINED doesn't seem like an option because we couldn't handle warn_strict_overflow properly. At this stage we're just recording a range that might or might not lead to strict-overflow assumptions later. It still feels like we should be able to do something here, but for now removing the code seems safest. It's also telling that there are no testsuite failures on SVE from doing this. gcc/ PR tree-optimization/97457 * value-range.cc (irange::set): Don't decay POLY_INT_CST ranges to integer ranges. gcc/testsuite/ PR tree-optimization/97457 * gcc.dg/vect/pr97457.c: New test. (cherry picked from commit 54ef7701a9dec8c923a12d1983f8a051ba88a7b9)
