On February 9, 2015 11:09:49 AM CET, Bin Cheng <bin.ch...@arm.com> wrote: >Hi, >As comments in the PR, root cause is GCC aggressively expand induction >variable's base. This patch avoids that by adding new parameter to >expand_simple_operations thus we can stop expansion whenever ssa var >referred by IV's step is encountered. As comments in patch, we could >stop >expanding at each ssa var referred by IV's step, but that's expensive >and >not likely to happen, this patch only extracts the first ssa var and >skips >expanding accordingly. >For the new test case, currently the loop body is bloated as below >after >IVOPT: > ><bb 5>: > # ci_28 = PHI <ci_12(D)(4), ci_17(6)> > # ivtmp.13_31 = PHI <ivtmp.13_25(4), ivtmp.13_27(6)> > ci_17 = ci_28 + 1; > _1 = (void *) ivtmp.13_31; > MEM[base: _1, offset: 0B] = 0; > ivtmp.13_27 = ivtmp.13_31 + _26; > _34 = (unsigned long) _13; > _35 = (unsigned long) flags_8(D); > _36 = _34 - _35; > _37 = (unsigned long) step_14; > _38 = _36 - _37; > _39 = ivtmp.13_27 + _38; > _40 = _39 + 3; > iter_33 = (long int) _40; > if (len_16(D) >= iter_33) > goto <bb 6>; > else > goto <bb 7>; > ><bb 6>: > goto <bb 5>; > >And it can be improved by this patch as below: > ><bb 5>: > # steps_28 = PHI <steps_12(D)(4), steps_17(6)> > # iter_29 = PHI <iter_15(4), iter_21(6)> > steps_17 = steps_28 + 1; > _31 = (sizetype) iter_29; > MEM[base: flags_8(D), index: _31, offset: 0B] = 0; > iter_21 = step_14 + iter_29; > if (len_16(D) >= iter_21) > goto <bb 6>; > else > goto <bb 7>; > ><bb 6>: > goto <bb 5>; > > >I think this is a corner case, it only changes several files' assembly >code >slightly in spec2k6. Among these files, only one of them is >regression.
Did you extract a testcase for it? Note that the IV step itself may be expanded Too much. I >looked into the regression and thought it was because of passes after >IVOPT. >The IVOPT dump is at least not worse than the original version. But different I presume. So how did you figure it regressed? Thanks, Richard. >Bootstrap and test on x86_64 and AArch64, so is it OK? > >2015-02-09 Bin Cheng <bin.ch...@arm.com> > > PR tree-optimization/64705 > * tree-ssa-loop-niter.h (expand_simple_operations): New parameter. > * tree-ssa-loop-niter.c (expand_simple_operations): New parameter. > (tree_simplify_using_condition_1, refine_bounds_using_guard) > (number_of_iterations_exit): Pass new argument to > expand_simple_operations. > * tree-ssa-loop-ivopts.c (extract_single_var_from_expr): New. > (find_bivs, find_givs_in_stmt_scev): Pass new argument to > expand_simple_operations. Call extract_single_var_from_expr. > (difference_cannot_overflow_p): Pass new argument to > expand_simple_operations. > >gcc/testsuite/ChangeLog >2015-02-09 Bin Cheng <bin.ch...@arm.com> > > PR tree-optimization/64705 > * gcc.dg/tree-ssa/pr64705.c: New test.