On Thu, Sep 22, 2016 at 12:10 PM, Pat Haugen <pthau...@linux.vnet.ibm.com> wrote: > I noticed the loop unroller peels an extra copy of the loop before it enters > the switch block code to round the iteration count to a multiple of the > unroll factor. This peeled copy is only needed for the case where the exit > test is at the beginning of the loop since in that case it inserts the test > for zero peel iterations before that peeled copy. > > This patch bumps the iteration count by 1 for loops with the exit at the end > so that it represents the number of times the loop body is executed, and > therefore removes the need to always execute that first peeled copy. With > this change, when the number of executions of the loop is an even multiple of > the unroll factor then the code will jump to the unrolled loop immediately > instead of executing all the switch code and peeled copies of the loop and > then falling into the unrolled loop. This change also reduces code size by > removing a peeled copy of the loop. > > Bootstrap/regtest on powerpc64le with no new regressions. Ok for trunk?
This patch or PR rtl-optimization/68212 * cfgloopmanip.c (duplicate_loop_to_header_edge): Use preheader edge frequency when computing scale factor for peeled copies. * loop-unroll.c (unroll_loop_runtime_iterations): Fix freq/count values for switch/peel blocks/edges. Caused a ~2.7-3.5% regression in coremarks with -funroll-all-loops. Thanks, Andrew > > > > 2016-09-22 Pat Haugen <pthau...@us.ibm.com> > > * loop-unroll.c (unroll_loop_runtime_iterations): Condition initial > loop peel to loops with exit test at the beginning. > >
