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// Copyright 2014 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef V8_COMPILER_OSR_H_
#define V8_COMPILER_OSR_H_
#include "src/zone/zone.h"
// TurboFan structures OSR graphs in a way that separates almost all phases of
// compilation from OSR implementation details. This is accomplished with
// special control nodes that are added at graph building time. In particular,
// the graph is built in such a way that typing still computes the best types
// and optimizations and lowering work unchanged. All that remains is to
// deconstruct the OSR artifacts before scheduling and code generation.
// Graphs built for OSR from the AstGraphBuilder are structured as follows:
// Start
// +-------------------^^-----+
// | |
// OsrNormalEntry OsrLoopEntry <-------------+
// | | |
// control flow before loop | A OsrValue
// | | | |
// | +------------------------+ | +-------+
// | | +-------------+ | | +--------+
// | | | | | | | |
// ( Loop )<-----------|------------------ ( phi ) |
// | | |
// loop body | backedge(s) |
// | | | |
// | +--------------+ B <-----+
// |
// end
// The control structure expresses the relationship that the loop has a separate
// entrypoint which corresponds to entering the loop directly from the middle
// of unoptimized code.
// Similarly, the values that come in from unoptimized code are represented with
// {OsrValue} nodes that merge into any phis associated with the OSR loop.
// In the above diagram, nodes {A} and {B} represent values in the "normal"
// graph that correspond to the values of those phis before the loop and on any
// backedges, respectively.
// To deconstruct OSR, we simply replace the uses of the {OsrNormalEntry}
// control node with {Dead} and {OsrLoopEntry} with start and run the
// {ControlReducer}. Control reduction propagates the dead control forward,
// essentially "killing" all the code before the OSR loop. The entrypoint to the
// loop corresponding to the "normal" entry path will also be removed, as well
// as the inputs to the loop phis, resulting in the reduced graph:
// Start
// Dead |^-------------------------+
// | | |
// | | |
// | | |
// disconnected, dead | A=dead OsrValue
// | |
// +------------------+ +------+
// | +-------------+ | +--------+
// | | | | | |
// ( Loop )<-----------|------------------ ( phi ) |
// | | |
// loop body | backedge(s) |
// | | | |
// | +--------------+ B <-----+
// |
// end
// Other than the presences of the OsrValue nodes, this is a normal, schedulable
// graph. OsrValue nodes are handled specially in the instruction selector to
// simply load from the unoptimized frame.
// For nested OSR loops, loop peeling must first be applied as many times as
// necessary in order to bring the OSR loop up to the top level (i.e. to be
// an outer loop).
namespace v8 {
namespace internal {
class CompilationInfo;
namespace compiler {
class JSGraph;
class CommonOperatorBuilder;
class Frame;
class Linkage;
// Encapsulates logic relating to OSR compilations as well has handles some
// details of the frame layout.
class OsrHelper {
public:
explicit OsrHelper(CompilationInfo* info);
// Only for testing.
OsrHelper(size_t parameter_count, size_t stack_slot_count)
: parameter_count_(parameter_count),
stack_slot_count_(stack_slot_count) {}
// Deconstructs the artificial {OsrNormalEntry} and rewrites the graph so
// that only the path corresponding to {OsrLoopEntry} remains.
void Deconstruct(JSGraph* jsgraph, CommonOperatorBuilder* common,
Zone* tmp_zone);
// Prepares the frame w.r.t. OSR.
void SetupFrame(Frame* frame);
// Returns the number of unoptimized frame slots for this OSR.
size_t UnoptimizedFrameSlots() { return stack_slot_count_; }
// Returns the environment index of the first stack slot.
static int FirstStackSlotIndex(int parameter_count) {
// n.b. unlike Crankshaft, TurboFan environments do not contain the context.
return 1 + parameter_count; // receiver + params
}
private:
size_t parameter_count_;
size_t stack_slot_count_;
};
} // namespace compiler
} // namespace internal
} // namespace v8
#endif // V8_COMPILER_OSR_H_
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