https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108038
--- Comment #2 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Jeff Law <l...@gcc.gnu.org>: https://gcc.gnu.org/g:a0f1f504b2c49a3695b91d3323d2e2419ef970db commit r15-3946-ga0f1f504b2c49a3695b91d3323d2e2419ef970db Author: Jovan Vukic <jovan.vu...@rt-rk.com> Date: Sun Sep 29 10:06:43 2024 -0600 [PATCH v2] RISC-V: Improve code generation for select of consecutive constants Based on the valuable feedback I received, I decided to implement the patch in the RTL pipeline. Since a similar optimization already exists in simplify_binary_operation_1, I chose to generalize my original approach and place it directly below that code. The expression (X xor C1) + C2 is simplified to X xor (C1 xor C2) under the conditions described in the patch. This is a more general optimization, but it still applies to the RISC-V case, which was my initial goal: long f1(long x, long y) { return (x > y) ? 2 : 3; } Before the patch, the generated assembly is: f1(long, long): sgt a0,a0,a1 xori a0,a0,1 addi a0,a0,2 ret After the patch, the generated assembly is: f1(long, long): sgt a0,a0,a1 xori a0,a0,3 ret The patch optimizes cases like x LT/GT y ? 2 : 3 (and x GE/LE y ? 3 : 2), as initially intended. Since this optimization is more general, I noticed it also optimizes cases like x < CONST ? 3 : 2 when CONST < 0. Iâve added tests for these cases as well. A bit of logic behind the patch: The equality A + B == A ^ B + 2 * (A & B) always holds true. This can be simplified to A ^ B if 2 * (A & B) == 0. In our case, we have A == X ^ C1, B == C2 and X is either 0 or 1. PR target/108038 gcc/ChangeLog: * simplify-rtx.cc (simplify_context::simplify_binary_operation_1): New simplification. gcc/testsuite/ChangeLog: * gcc.target/riscv/slt-1.c: New test.
