# HG changeset patch # User never # Date 1301995906 25200 # Node ID 8e77e1f261884c35e6004be05f31057137a8c2bf # Parent 479b4b4b695056708ede7b1082a6aa7ce41b83e9# Parent 03f2be00fa216cb73134b52c7812e30ab8eb85bf Merge diff -r 479b4b4b6950 -r 8e77e1f26188 src/share/vm/opto/loopTransform.cpp --- a/src/share/vm/opto/loopTransform.cpp Tue Apr 05 00:31:09 2011 -0700 +++ b/src/share/vm/opto/loopTransform.cpp Tue Apr 05 02:31:46 2011 -0700 @@ -522,34 +522,40 @@ loop->record_for_igvn(); } +#define EMPTY_LOOP_SIZE 7 // number of nodes in an empty loop + //------------------------------policy_maximally_unroll------------------------ -// Return exact loop trip count, or 0 if not maximally unrolling +// Calculate exact loop trip count and return true if loop can be maximally +// unrolled. bool IdealLoopTree::policy_maximally_unroll( PhaseIdealLoop *phase ) const { CountedLoopNode *cl = _head->as_CountedLoop(); assert(cl->is_normal_loop(), ""); + if (!cl->is_valid_counted_loop()) + return false; // Malformed counted loop Node *init_n = cl->init_trip(); Node *limit_n = cl->limit(); // Non-constant bounds if (init_n == NULL || !init_n->is_Con() || - limit_n == NULL || !limit_n->is_Con() || - // protect against stride not being a constant - !cl->stride_is_con()) { + limit_n == NULL || !limit_n->is_Con()) { return false; } - int init = init_n->get_int(); - int limit = limit_n->get_int(); - int span = limit - init; - int stride = cl->stride_con(); + // Use longs to avoid integer overflow. + int stride_con = cl->stride_con(); + long init_con = cl->init_trip()->get_int(); + long limit_con = cl->limit()->get_int(); + int stride_m = stride_con - (stride_con > 0 ? 1 : -1); + long trip_cnt = (limit_con - init_con + stride_m)/stride_con; - if (init >= limit || stride > span) { + // Note, max_jint is used to indicate unknown trip count. + if (trip_cnt <= 0 || trip_cnt >= (long)max_jint) { // return a false (no maximally unroll) and the regular unroll/peel // route will make a small mess which CCP will fold away. return false; } - uint trip_count = span/stride; // trip_count can be greater than 2 Gig. - assert( (int)trip_count*stride == span, "must divide evenly" ); + uint trip_count = (uint)trip_cnt; + cl->set_trip_count(trip_count); // Real policy: if we maximally unroll, does it get too big? // Allow the unrolled mess to get larger than standard loop @@ -557,15 +563,29 @@ uint body_size = _body.size(); uint unroll_limit = (uint)LoopUnrollLimit * 4; assert( (intx)unroll_limit == LoopUnrollLimit * 4, "LoopUnrollLimit must fit in 32bits"); - cl->set_trip_count(trip_count); if (trip_count > unroll_limit || body_size > unroll_limit) { return false; } + // Take into account that after unroll conjoined heads and tails will fold, + // otherwise policy_unroll() may allow more unrolling than max unrolling. + uint new_body_size = EMPTY_LOOP_SIZE + (body_size - EMPTY_LOOP_SIZE) * trip_count; + uint tst_body_size = (new_body_size - EMPTY_LOOP_SIZE) / trip_count + EMPTY_LOOP_SIZE; + if (body_size != tst_body_size) // Check for int overflow + return false; + if (new_body_size > unroll_limit || + // Unrolling can result in a large amount of node construction + new_body_size >= MaxNodeLimit - phase->C->unique()) { + return false; + } + // Currently we don't have policy to optimize one iteration loops. // Maximally unrolling transformation is used for that: // it is peeled and the original loop become non reachable (dead). - if (trip_count == 1) + // Also fully unroll a loop with few iterations regardless next + // conditions since following loop optimizations will split + // such loop anyway (pre-main-post). + if (trip_count <= 3) return true; // Do not unroll a loop with String intrinsics code. @@ -582,17 +602,7 @@ } // switch } - if (body_size <= unroll_limit) { - uint new_body_size = body_size * trip_count; - if (new_body_size <= unroll_limit && - body_size == new_body_size / trip_count && - // Unrolling can result in a large amount of node construction - new_body_size < MaxNodeLimit - phase->C->unique()) { - return true; // maximally unroll - } - } - - return false; // Do not maximally unroll + return true; // Do maximally unroll } @@ -604,12 +614,15 @@ CountedLoopNode *cl = _head->as_CountedLoop(); assert(cl->is_normal_loop() || cl->is_main_loop(), ""); - // protect against stride not being a constant - if (!cl->stride_is_con()) return false; + if (!cl->is_valid_counted_loop()) + return false; // Malformed counted loop // protect against over-unrolling if (cl->trip_count() <= 1) return false; + // Check for stride being a small enough constant + if (abs(cl->stride_con()) > (1<<3)) return false; + int future_unroll_ct = cl->unrolled_count() * 2; // Don't unroll if the next round of unrolling would push us @@ -690,9 +703,6 @@ return false; } - // Check for stride being a small enough constant - if (abs(cl->stride_con()) > (1<<3)) return false; - // Unroll once! (Each trip will soon do double iterations) return true; } @@ -1086,7 +1096,11 @@ tty->print("Unrolling "); loop->dump_head(); } else if (TraceLoopOpts) { - tty->print("Unroll %d ", loop_head->unrolled_count()*2); + if (loop_head->trip_count() < LoopUnrollLimit) { + tty->print("Unroll %d(%2d) ", loop_head->unrolled_count()*2, loop_head->trip_count()); + } else { + tty->print("Unroll %d ", loop_head->unrolled_count()*2); + } loop->dump_head(); } #endif @@ -1761,7 +1775,7 @@ // have on the last iteration. This will break the loop. bool IdealLoopTree::policy_do_remove_empty_loop( PhaseIdealLoop *phase ) { // Minimum size must be empty loop - if (_body.size() > 7/*number of nodes in an empty loop*/) + if (_body.size() > EMPTY_LOOP_SIZE) return false; if (!_head->is_CountedLoop()) @@ -1887,6 +1901,12 @@ } } + // Skip next optimizations if running low on nodes. Note that + // policy_unswitching and policy_maximally_unroll have this check. + uint nodes_left = MaxNodeLimit - phase->C->unique(); + if ((2 * _body.size()) > nodes_left) { + return true; + } // Counted loops may be peeled, may need some iterations run up // front for RCE, and may want to align loop refs to a cache