| // 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.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_ |