srdjan@google.com
b6d1804071
Reenable some Smi check eliminations. Soon Florian will factor out class checks into own instruction where the elimination will be moved. Implement more ResultCid()-s, removed TODO to make it asbtract because almost all computations return kDynamicCid. Review URL: https://chromiumcodereview.appspot.com//10827387 git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@10865 260f80e4-7a28-3924-810f-c04153c831b5
469 lines
17 KiB
C++
469 lines
17 KiB
C++
// Copyright (c) 2012, the Dart project authors. Please see the AUTHORS file
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// for details. All rights reserved. Use of this source code is governed by a
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// BSD-style license that can be found in the LICENSE file.
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#include "vm/flow_graph.h"
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#include "vm/bit_vector.h"
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#include "vm/flow_graph_builder.h"
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#include "vm/intermediate_language.h"
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#include "vm/longjump.h"
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namespace dart {
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FlowGraph::FlowGraph(const FlowGraphBuilder& builder,
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GraphEntryInstr* graph_entry)
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: parent_(),
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assigned_vars_(),
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current_ssa_temp_index_(0),
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parsed_function_(builder.parsed_function()),
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copied_parameter_count_(builder.copied_parameter_count()),
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non_copied_parameter_count_(builder.non_copied_parameter_count()),
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stack_local_count_(builder.stack_local_count()),
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graph_entry_(graph_entry),
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preorder_(),
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postorder_(),
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reverse_postorder_() {
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DiscoverBlocks();
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}
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void FlowGraph::DiscoverBlocks() {
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// Initialize state.
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preorder_.TruncateTo(0);
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postorder_.TruncateTo(0);
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reverse_postorder_.TruncateTo(0);
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parent_.TruncateTo(0);
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assigned_vars_.TruncateTo(0);
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// Perform a depth-first traversal of the graph to build preorder and
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// postorder block orders.
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graph_entry_->DiscoverBlocks(NULL, // Entry block predecessor.
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&preorder_,
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&postorder_,
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&parent_,
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&assigned_vars_,
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variable_count(),
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non_copied_parameter_count());
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// Number blocks in reverse postorder.
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intptr_t block_count = postorder_.length();
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for (intptr_t i = 0; i < block_count; ++i) {
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postorder_[i]->set_block_id(block_count - i - 1);
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reverse_postorder_.Add(postorder_[block_count - i - 1]);
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}
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// Link instructions backwards for optimized compilation.
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// TODO(zerny): The builder should do this at construction time.
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for (intptr_t i = 0; i < block_count; ++i) {
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BlockEntryInstr* entry = postorder_[i];
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Instruction* previous = entry;
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for (ForwardInstructionIterator it(entry); !it.Done(); it.Advance()) {
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Instruction* current = it.Current();
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current->set_previous(previous);
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previous = current;
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}
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}
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}
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void FlowGraph::ComputeSSA() {
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GrowableArray<BitVector*> dominance_frontier;
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ComputeDominators(&preorder_, &parent_, &dominance_frontier);
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InsertPhis(preorder_, assigned_vars_, dominance_frontier);
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GrowableArray<PhiInstr*> live_phis;
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// Rename uses to reference inserted phis where appropriate.
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// Collect phis that reach a non-environment use.
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Rename(&live_phis);
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// Propagate alive mark transitively from alive phis.
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MarkLivePhis(&live_phis);
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}
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// Compute immediate dominators and the dominance frontier for each basic
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// block. As a side effect of the algorithm, sets the immediate dominator
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// of each basic block.
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//
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// preorder: an input list of basic block entries in preorder. The
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// algorithm relies on the block ordering.
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//
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// parent: an input parameter encoding a depth-first spanning tree of
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// the control flow graph. The array maps the preorder block
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// number of a block to the preorder block number of its spanning
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// tree parent.
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//
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// dominance_frontier: an output parameter encoding the dominance frontier.
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// The array maps the preorder block number of a block to the set of
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// (preorder block numbers of) blocks in the dominance frontier.
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void FlowGraph::ComputeDominators(
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GrowableArray<BlockEntryInstr*>* preorder,
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GrowableArray<intptr_t>* parent,
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GrowableArray<BitVector*>* dominance_frontier) {
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// Use the SEMI-NCA algorithm to compute dominators. This is a two-pass
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// version of the Lengauer-Tarjan algorithm (LT is normally three passes)
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// that eliminates a pass by using nearest-common ancestor (NCA) to
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// compute immediate dominators from semidominators. It also removes a
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// level of indirection in the link-eval forest data structure.
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//
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// The algorithm is described in Georgiadis, Tarjan, and Werneck's
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// "Finding Dominators in Practice".
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// See http://www.cs.princeton.edu/~rwerneck/dominators/ .
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// All arrays are maps between preorder basic-block numbers.
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intptr_t size = parent->length();
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GrowableArray<intptr_t> idom(size); // Immediate dominator.
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GrowableArray<intptr_t> semi(size); // Semidominator.
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GrowableArray<intptr_t> label(size); // Label for link-eval forest.
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// 1. First pass: compute semidominators as in Lengauer-Tarjan.
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// Semidominators are computed from a depth-first spanning tree and are an
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// approximation of immediate dominators.
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// Use a link-eval data structure with path compression. Implement path
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// compression in place by mutating the parent array. Each block has a
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// label, which is the minimum block number on the compressed path.
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// Initialize idom, semi, and label used by SEMI-NCA. Initialize the
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// dominance frontier output array.
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for (intptr_t i = 0; i < size; ++i) {
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idom.Add((*parent)[i]);
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semi.Add(i);
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label.Add(i);
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dominance_frontier->Add(new BitVector(size));
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}
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// Loop over the blocks in reverse preorder (not including the graph
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// entry).
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for (intptr_t block_index = size - 1; block_index >= 1; --block_index) {
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// Loop over the predecessors.
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BlockEntryInstr* block = (*preorder)[block_index];
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for (intptr_t i = 0, count = block->PredecessorCount(); i < count; ++i) {
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BlockEntryInstr* pred = block->PredecessorAt(i);
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ASSERT(pred != NULL);
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// Look for the semidominator by ascending the semidominator path
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// starting from pred.
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intptr_t pred_index = pred->preorder_number();
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intptr_t best = pred_index;
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if (pred_index > block_index) {
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CompressPath(block_index, pred_index, parent, &label);
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best = label[pred_index];
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}
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// Update the semidominator if we've found a better one.
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semi[block_index] = Utils::Minimum(semi[block_index], semi[best]);
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}
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// Now use label for the semidominator.
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label[block_index] = semi[block_index];
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}
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// 2. Compute the immediate dominators as the nearest common ancestor of
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// spanning tree parent and semidominator, for all blocks except the entry.
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for (intptr_t block_index = 1; block_index < size; ++block_index) {
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intptr_t dom_index = idom[block_index];
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while (dom_index > semi[block_index]) {
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dom_index = idom[dom_index];
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}
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idom[block_index] = dom_index;
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(*preorder)[block_index]->set_dominator((*preorder)[dom_index]);
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(*preorder)[dom_index]->AddDominatedBlock((*preorder)[block_index]);
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}
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// 3. Now compute the dominance frontier for all blocks. This is
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// algorithm in "A Simple, Fast Dominance Algorithm" (Figure 5), which is
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// attributed to a paper by Ferrante et al. There is no bookkeeping
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// required to avoid adding a block twice to the same block's dominance
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// frontier because we use a set to represent the dominance frontier.
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for (intptr_t block_index = 0; block_index < size; ++block_index) {
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BlockEntryInstr* block = (*preorder)[block_index];
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intptr_t count = block->PredecessorCount();
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if (count <= 1) continue;
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for (intptr_t i = 0; i < count; ++i) {
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BlockEntryInstr* runner = block->PredecessorAt(i);
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while (runner != block->dominator()) {
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(*dominance_frontier)[runner->preorder_number()]->Add(block_index);
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runner = runner->dominator();
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}
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}
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}
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}
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void FlowGraph::CompressPath(intptr_t start_index,
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intptr_t current_index,
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GrowableArray<intptr_t>* parent,
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GrowableArray<intptr_t>* label) {
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intptr_t next_index = (*parent)[current_index];
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if (next_index > start_index) {
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CompressPath(start_index, next_index, parent, label);
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(*label)[current_index] =
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Utils::Minimum((*label)[current_index], (*label)[next_index]);
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(*parent)[current_index] = (*parent)[next_index];
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}
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}
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void FlowGraph::InsertPhis(
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const GrowableArray<BlockEntryInstr*>& preorder,
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const GrowableArray<BitVector*>& assigned_vars,
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const GrowableArray<BitVector*>& dom_frontier) {
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const intptr_t block_count = preorder.length();
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// Map preorder block number to the highest variable index that has a phi
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// in that block. Use it to avoid inserting multiple phis for the same
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// variable.
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GrowableArray<intptr_t> has_already(block_count);
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// Map preorder block number to the highest variable index for which the
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// block went on the worklist. Use it to avoid adding the same block to
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// the worklist more than once for the same variable.
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GrowableArray<intptr_t> work(block_count);
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// Initialize has_already and work.
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for (intptr_t block_index = 0; block_index < block_count; ++block_index) {
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has_already.Add(-1);
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work.Add(-1);
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}
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// Insert phis for each variable in turn.
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GrowableArray<BlockEntryInstr*> worklist;
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for (intptr_t var_index = 0; var_index < variable_count(); ++var_index) {
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// Add to the worklist each block containing an assignment.
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for (intptr_t block_index = 0; block_index < block_count; ++block_index) {
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if (assigned_vars[block_index]->Contains(var_index)) {
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work[block_index] = var_index;
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worklist.Add(preorder[block_index]);
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}
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}
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while (!worklist.is_empty()) {
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BlockEntryInstr* current = worklist.Last();
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worklist.RemoveLast();
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// Ensure a phi for each block in the dominance frontier of current.
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for (BitVector::Iterator it(dom_frontier[current->preorder_number()]);
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!it.Done();
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it.Advance()) {
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int index = it.Current();
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if (has_already[index] < var_index) {
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BlockEntryInstr* block = preorder[index];
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ASSERT(block->IsJoinEntry());
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block->AsJoinEntry()->InsertPhi(var_index, variable_count());
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has_already[index] = var_index;
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if (work[index] < var_index) {
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work[index] = var_index;
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worklist.Add(block);
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}
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}
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}
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}
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}
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}
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void FlowGraph::Rename(GrowableArray<PhiInstr*>* live_phis) {
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// TODO(fschneider): Support catch-entry.
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if (graph_entry_->SuccessorCount() > 1) {
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Bailout("Catch-entry support in SSA.");
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}
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// Initialize start environment.
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GrowableArray<Value*> start_env(variable_count());
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for (intptr_t i = 0; i < parameter_count(); ++i) {
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ParameterInstr* param = new ParameterInstr(i);
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param->set_ssa_temp_index(alloc_ssa_temp_index()); // New SSA temp.
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start_env.Add(new UseVal(param));
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}
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// All locals are initialized with #null.
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Value* null_value = new ConstantVal(Object::ZoneHandle());
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while (start_env.length() < variable_count()) {
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start_env.Add(null_value);
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}
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graph_entry_->set_start_env(
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new Environment(start_env, non_copied_parameter_count_));
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BlockEntryInstr* normal_entry = graph_entry_->SuccessorAt(0);
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ASSERT(normal_entry != NULL); // Must have entry.
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GrowableArray<Value*> env(variable_count());
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env.AddArray(start_env);
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RenameRecursive(normal_entry, &env, live_phis);
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}
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// Helper to a copy a value iff it is a UseVal.
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static Value* CopyValue(Value* value) {
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return value->IsUse()
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? new UseVal(value->AsUse()->definition())
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: value;
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}
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void FlowGraph::RenameRecursive(BlockEntryInstr* block_entry,
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GrowableArray<Value*>* env,
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GrowableArray<PhiInstr*>* live_phis) {
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// 1. Process phis first.
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if (block_entry->IsJoinEntry()) {
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JoinEntryInstr* join = block_entry->AsJoinEntry();
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if (join->phis() != NULL) {
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for (intptr_t i = 0; i < join->phis()->length(); ++i) {
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PhiInstr* phi = (*join->phis())[i];
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if (phi != NULL) {
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(*env)[i] = new UseVal(phi);
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phi->set_ssa_temp_index(alloc_ssa_temp_index()); // New SSA temp.
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}
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}
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}
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}
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// 2. Process normal instructions.
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for (ForwardInstructionIterator it(block_entry); !it.Done(); it.Advance()) {
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Instruction* current = it.Current();
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// Attach current environment to the instruction. First, each instruction
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// gets a full copy of the environment. Later we optimize this by
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// eliminating unnecessary environments.
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current->set_env(new Environment(*env, non_copied_parameter_count_));
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// 2a. Handle uses:
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// Update expression stack environment for each use.
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// For each use of a LoadLocal or StoreLocal: Replace it with the value
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// from the environment.
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for (intptr_t i = current->InputCount() - 1; i >= 0; --i) {
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Value* v = current->InputAt(i);
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if (!v->IsUse()) continue;
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// Update expression stack.
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ASSERT(env->length() > variable_count());
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Value* input_value = env->Last();
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ASSERT(input_value->IsUse());
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env->RemoveLast();
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BindInstr* as_bind = v->AsUse()->definition()->AsBind();
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if ((as_bind != NULL) &&
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(as_bind->computation()->IsLoadLocal() ||
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as_bind->computation()->IsStoreLocal())) {
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// Assert exactly one use.
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ASSERT(as_bind->use_list() == v);
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ASSERT(as_bind->use_list()->next_use() == NULL);
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// Remove the use, its definition and copy the environment value.
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v->RemoveFromUseList();
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as_bind->RemoveFromGraph();
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current->SetInputAt(i, CopyValue(input_value));
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}
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}
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// Drop pushed arguments for calls.
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for (intptr_t j = 0; j < current->ArgumentCount(); j++) {
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env->RemoveLast();
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}
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// 2b. Handle LoadLocal and StoreLocal.
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// For each LoadLocal: Remove it from the graph.
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// For each StoreLocal: Remove it from the graph and update the environment.
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BindInstr* bind = current->AsBind();
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if (bind != NULL) {
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LoadLocalComp* load = bind->computation()->AsLoadLocal();
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StoreLocalComp* store = bind->computation()->AsStoreLocal();
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if ((load != NULL) || (store != NULL)) {
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intptr_t index;
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if (store != NULL) {
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index = store->local().BitIndexIn(non_copied_parameter_count_);
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// Update renaming environment.
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(*env)[index] = store->value();
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} else {
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// The graph construction ensures we do not have an unused LoadLocal
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// computation.
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ASSERT(bind->is_used());
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index = load->local().BitIndexIn(non_copied_parameter_count_);
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Value* value = (*env)[index];
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if (value->IsUse()) {
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PhiInstr* phi = value->AsUse()->definition()->AsPhi();
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if ((phi != NULL) && !phi->is_alive()) {
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phi->mark_alive();
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live_phis->Add(phi);
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}
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}
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}
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// Update expression stack or remove from graph.
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if (bind->is_used()) {
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// Assert exactly one use.
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ASSERT(bind->use_list() != NULL);
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ASSERT(bind->use_list()->next_use() == NULL);
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env->Add(CopyValue((*env)[index]));
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// We remove load/store instructions when we find their use in 2a.
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} else {
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it.RemoveCurrentFromGraph();
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}
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} else {
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// Not a load or store.
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if (bind->is_used()) {
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// Assign fresh SSA temporary and update expression stack.
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bind->set_ssa_temp_index(alloc_ssa_temp_index());
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env->Add(new UseVal(bind));
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}
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}
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}
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// 2c. Handle pushed argument.
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PushArgumentInstr* push = current->AsPushArgument();
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if (push != NULL) {
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env->Add(new UseVal(push));
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}
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}
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// 3. Process dominated blocks.
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for (intptr_t i = 0; i < block_entry->dominated_blocks().length(); ++i) {
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BlockEntryInstr* block = block_entry->dominated_blocks()[i];
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GrowableArray<Value*> new_env(env->length());
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new_env.AddArray(*env);
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RenameRecursive(block, &new_env, live_phis);
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}
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// 4. Process successor block. We have edge-split form, so that only blocks
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// with one successor can have a join block as successor.
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if ((block_entry->last_instruction()->SuccessorCount() == 1) &&
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block_entry->last_instruction()->SuccessorAt(0)->IsJoinEntry()) {
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JoinEntryInstr* successor =
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block_entry->last_instruction()->SuccessorAt(0)->AsJoinEntry();
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intptr_t pred_index = successor->IndexOfPredecessor(block_entry);
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ASSERT(pred_index >= 0);
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if (successor->phis() != NULL) {
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for (intptr_t i = 0; i < successor->phis()->length(); ++i) {
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PhiInstr* phi = (*successor->phis())[i];
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if (phi != NULL) {
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// Rename input operand and make a copy if it is a UseVal.
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phi->SetInputAt(pred_index, CopyValue((*env)[i]));
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}
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}
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}
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}
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}
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void FlowGraph::MarkLivePhis(GrowableArray<PhiInstr*>* live_phis) {
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while (!live_phis->is_empty()) {
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PhiInstr* phi = live_phis->Last();
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live_phis->RemoveLast();
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for (intptr_t i = 0; i < phi->InputCount(); i++) {
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Value* val = phi->InputAt(i);
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if (!val->IsUse()) continue;
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PhiInstr* used_phi = val->AsUse()->definition()->AsPhi();
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if ((used_phi != NULL) && !used_phi->is_alive()) {
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used_phi->mark_alive();
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live_phis->Add(used_phi);
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}
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}
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}
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}
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void FlowGraph::Bailout(const char* reason) const {
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const char* kFormat = "FlowGraph Bailout: %s %s";
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const char* function_name = parsed_function_.function().ToCString();
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intptr_t len = OS::SNPrint(NULL, 0, kFormat, function_name, reason) + 1;
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char* chars = Isolate::Current()->current_zone()->Alloc<char>(len);
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OS::SNPrint(chars, len, kFormat, function_name, reason);
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const Error& error = Error::Handle(
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LanguageError::New(String::Handle(String::New(chars))));
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Isolate::Current()->long_jump_base()->Jump(1, error);
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}
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} // namespace dart
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