https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110148
--- Comment #5 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Lili Cui <cuil...@gcc.gnu.org>: https://gcc.gnu.org/g:4633e38cd22c5e51fac984124c7627be912d0999 commit r14-2185-g4633e38cd22c5e51fac984124c7627be912d0999 Author: Lili Cui <lili....@intel.com> Date: Thu Jun 29 06:51:56 2023 +0000 Avoid adding loop-carried ops to long chains Avoid adding loop-carried ops to long chains, otherwise the whole chain will have dependencies across the loop iteration. Just keep loop-carried ops in a separate chain. E.g. x_1 = phi(x_0, x_2) y_1 = phi(y_0, y_2) a + b + c + d + e + x1 + y1 SSA1 = a + b; SSA2 = c + d; SSA3 = SSA1 + e; SSA4 = SSA3 + SSA2; SSA5 = x1 + y1; SSA6 = SSA4 + SSA5; With the patch applied, these test cases improved by 32%~100%. S242: for (int i = 1; i < LEN_1D; ++i) { a[i] = a[i - 1] + s1 + s2 + b[i] + c[i] + d[i];} Case 1: for (int i = 1; i < LEN_1D; ++i) { a[i] = a[i - 1] + s1 + s2 + b[i] + c[i] + d[i] + e[i];} Case 2: for (int i = 1; i < LEN_1D; ++i) { a[i] = a[i - 1] + b[i - 1] + s1 + s2 + b[i] + c[i] + d[i] + e[i];} The value is the execution time A: original version B: with FMA patch g:e5405f065bace0685cb3b8878d1dfc7a6e7ef409(base on A) C: with current patch(base on B) A B C B/A C/A s242 2.859 5.152 2.859 1.802028681 1 case 1 5.489 5.488 3.511 0.999818 0.64 case 2 7.216 7.499 4.885 1.039218 0.68 gcc/ChangeLog: PR tree-optimization/110148 * tree-ssa-reassoc.cc (rewrite_expr_tree_parallel): Handle loop-carried ops in this function.
