https://gcc.gnu.org/bugzilla/show_bug.cgi?id=49749
--- Comment #18 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Ilya Leoshkevich <i...@gcc.gnu.org>: https://gcc.gnu.org/g:dbed1c8693c6b5cb02c903cea91db574200bd513 commit r12-3922-gdbed1c8693c6b5cb02c903cea91db574200bd513 Author: Ilya Leoshkevich <i...@linux.ibm.com> Date: Wed Jun 24 01:30:47 2020 +0200 reassoc: Propagate PHI_LOOP_BIAS along single uses PR tree-optimization/49749 introduced code that shortens dependency chains containing loop accumulators by placing them last on operand lists of associative operations. 456.hmmer benchmark on s390 could benefit from this, however, the code that needs it modifies loop accumulator before using it, and since only so-called loop-carried phis are are treated as loop accumulators, the code in the present form doesn't really help. According to Bill Schmidt - the original author - such a conservative approach was chosen so as to avoid unnecessarily swapping operands, which might cause unpredictable effects. However, giving special treatment to forms of loop accumulators is acceptable. The definition of loop-carried phi is: it's a single-use phi, which is used in the same innermost loop it's defined in, at least one argument of which is defined in the same innermost loop as the phi itself. Given this, it seems natural to treat single uses of such phis as phis themselves. gcc/ChangeLog: * tree-ssa-reassoc.c (biased_names): New global. (propagate_bias_p): New function. (loop_carried_phi): Remove. (propagate_rank): Propagate bias along single uses. (get_rank): Update biased_names when needed.
