https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116355
--- Comment #4 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Filip Kastl <phe...@gcc.gnu.org>: https://gcc.gnu.org/g:1c4b9826bd0d5ac471543c68f097d80b1969f599 commit r15-3256-g1c4b9826bd0d5ac471543c68f097d80b1969f599 Author: Filip Kastl <fka...@suse.cz> Date: Wed Aug 28 15:47:44 2024 +0200 gimple ssa: switchconv: Use __builtin_popcount and support more types in exp transform [PR116355] The gen_pow2p function generates (a & -a) == a as a fallback for POPCOUNT (a) == 1. Not only is the bitmagic not equivalent to POPCOUNT (a) == 1 but it also introduces UB (consider signed a = INT_MIN). This patch rewrites gen_pow2p to always use __builtin_popcount instead. This means that what the end result GIMPLE code is gets decided by an already existing machinery in a later pass. That is a cleaner solution I think. This existing machinery also uses a ^ (a - 1) > a - 1 which is the correct bitmagic. While rewriting gen_pow2p I had to add logic for converting the operand's type to a type that __builtin_popcount accepts. I naturally also added this logic to gen_log2. Thanks to this, exponential index transform gains the capability to handle all operand types with precision at most that of long long int. gcc/ChangeLog: PR tree-optimization/116355 * tree-switch-conversion.cc (can_log2): Add capability to suggest converting the operand to a different type. (gen_log2): Add capability to generate a conversion in case the operand is of a type incompatible with the logarithm operation. (can_pow2p): New function. (gen_pow2p): Rewrite to use __builtin_popcount instead of manually inserting an internal fn call or bitmagic. Also add capability to generate a conversion. (switch_conversion::is_exp_index_transform_viable): Call can_pow2p. Store types suggested by can_log2 and gen_log2. (switch_conversion::exp_index_transform): Params of gen_pow2p and gen_log2 changed so update their calls. * tree-switch-conversion.h: Add m_exp_index_transform_log2_type and m_exp_index_transform_pow2p_type to switch_conversion class to track type conversions needed to generate the "is power of 2" and logarithm operations. gcc/testsuite/ChangeLog: PR tree-optimization/116355 * gcc.target/i386/switch-exp-transform-1.c: Don't test for presence of POPCOUNT internal fn after switch conversion. Test for it after __builtin_popcount has had a chance to get expanded. * gcc.target/i386/switch-exp-transform-3.c: Also test char and short. Signed-off-by: Filip Kastl <fka...@suse.cz>
