https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112807
--- Comment #3 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Jakub Jelinek <ja...@gcc.gnu.org>: https://gcc.gnu.org/g:eef6aea3052b4b8a60df211015dafcb4573d19fb commit r14-6095-geef6aea3052b4b8a60df211015dafcb4573d19fb Author: Jakub Jelinek <ja...@redhat.com> Date: Sun Dec 3 17:54:03 2023 +0100 lower-bitint: Fix up lower_addsub_overflow [PR112807] lower_addsub_overflow uses handle_cast or handle_operand to extract current limb from the operands. Both of those functions heavily assume that they return a large or huge BITINT_TYPE. The problem in the testcase is that this is violated. Normally, lower_addsub_overflow isn't even called if neither the return's type element type nor any of the operand is large/huge BITINT_TYPE (on x86_64 129+ bits), for middle BITINT_TYPE (on x86_64 65-128 bits) some other code casts such operands to {,unsigned }__int128. In the testcase the result is complex unsigned, so small, but one of the arguments is _BitInt(256), so lower_addsub_overflow is called. But range_for_prec asks the ranger for ranges of the operands and in this case the first argument has [0, 0xffffffff] range and second [-2, 1], so unsigned 32-bit and signed 2-bit, and in such case the code for handle_operand/handle_cast purposes would use the _BitInt(256) type for the first operand (ok), but because prec3 aka maximum of result precision and the VRP computes ranges of the arguments is 32, use cast to 32-bit BITINT_TYPE, which is why it didn't work correctly. The following patch ensures that in such cases we use handle_cast to the type of the other argument. Perhaps incrementally, we could try to optimize this in an earlier phase, see that while the .{ADD,SUB}_OVERFLOW has large/huge _BitInt argument, as ranger says it fits into a smaller type, add a cast of the larger argument to the smaller precision type in which it fits. Either in gimple_lower_bitint, or match.pd. An argument for the latter is that e.g. complex unsigned .ADD_OVERFLOW (unsigned_long_long_arg, unsigned_arg) where ranger says unsigned_long_long_arg fits into unsigned 32-bit could be also more efficient as .ADD_OVERFLOW ((unsigned) unsigned_long_long_arg, unsigned_arg) 2023-12-03 Jakub Jelinek <ja...@redhat.com> PR middle-end/112807 * gimple-lower-bitint.cc (bitint_large_huge::lower_addsub_overflow): When choosing type0 and type1 types, if prec3 has small/middle bitint kind, use maximum of type0 and type1's precision instead of prec3. * gcc.dg/bitint-46.c: New test.
