1 // Copyright 2014 the V8 project authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style license that can be 3 // found in the LICENSE file. 4 5 #ifndef V8_COMPILER_OSR_H_ 6 #define V8_COMPILER_OSR_H_ 7 8 #include "src/zone/zone.h" 9 10 // TurboFan structures OSR graphs in a way that separates almost all phases of 11 // compilation from OSR implementation details. This is accomplished with 12 // special control nodes that are added at graph building time. In particular, 13 // the graph is built in such a way that typing still computes the best types 14 // and optimizations and lowering work unchanged. All that remains is to 15 // deconstruct the OSR artifacts before scheduling and code generation. 16 17 // Graphs built for OSR from the AstGraphBuilder are structured as follows: 18 // Start 19 // +-------------------^^-----+ 20 // | | 21 // OsrNormalEntry OsrLoopEntry <-------------+ 22 // | | | 23 // control flow before loop | A OsrValue 24 // | | | | 25 // | +------------------------+ | +-------+ 26 // | | +-------------+ | | +--------+ 27 // | | | | | | | | 28 // ( Loop )<-----------|------------------ ( phi ) | 29 // | | | 30 // loop body | backedge(s) | 31 // | | | | 32 // | +--------------+ B <-----+ 33 // | 34 // end 35 36 // The control structure expresses the relationship that the loop has a separate 37 // entrypoint which corresponds to entering the loop directly from the middle 38 // of unoptimized code. 39 // Similarly, the values that come in from unoptimized code are represented with 40 // {OsrValue} nodes that merge into any phis associated with the OSR loop. 41 // In the above diagram, nodes {A} and {B} represent values in the "normal" 42 // graph that correspond to the values of those phis before the loop and on any 43 // backedges, respectively. 44 45 // To deconstruct OSR, we simply replace the uses of the {OsrNormalEntry} 46 // control node with {Dead} and {OsrLoopEntry} with start and run the 47 // {ControlReducer}. Control reduction propagates the dead control forward, 48 // essentially "killing" all the code before the OSR loop. The entrypoint to the 49 // loop corresponding to the "normal" entry path will also be removed, as well 50 // as the inputs to the loop phis, resulting in the reduced graph: 51 52 // Start 53 // Dead |^-------------------------+ 54 // | | | 55 // | | | 56 // | | | 57 // disconnected, dead | A=dead OsrValue 58 // | | 59 // +------------------+ +------+ 60 // | +-------------+ | +--------+ 61 // | | | | | | 62 // ( Loop )<-----------|------------------ ( phi ) | 63 // | | | 64 // loop body | backedge(s) | 65 // | | | | 66 // | +--------------+ B <-----+ 67 // | 68 // end 69 70 // Other than the presences of the OsrValue nodes, this is a normal, schedulable 71 // graph. OsrValue nodes are handled specially in the instruction selector to 72 // simply load from the unoptimized frame. 73 74 // For nested OSR loops, loop peeling must first be applied as many times as 75 // necessary in order to bring the OSR loop up to the top level (i.e. to be 76 // an outer loop). 77 78 namespace v8 { 79 namespace internal { 80 81 class CompilationInfo; 82 83 namespace compiler { 84 85 class JSGraph; 86 class CommonOperatorBuilder; 87 class Frame; 88 class Linkage; 89 90 // Encapsulates logic relating to OSR compilations as well has handles some 91 // details of the frame layout. 92 class OsrHelper { 93 public: 94 explicit OsrHelper(CompilationInfo* info); 95 // Only for testing. OsrHelper(size_t parameter_count,size_t stack_slot_count)96 OsrHelper(size_t parameter_count, size_t stack_slot_count) 97 : parameter_count_(parameter_count), 98 stack_slot_count_(stack_slot_count) {} 99 100 // Deconstructs the artificial {OsrNormalEntry} and rewrites the graph so 101 // that only the path corresponding to {OsrLoopEntry} remains. 102 void Deconstruct(JSGraph* jsgraph, CommonOperatorBuilder* common, 103 Zone* tmp_zone); 104 105 // Prepares the frame w.r.t. OSR. 106 void SetupFrame(Frame* frame); 107 108 // Returns the number of unoptimized frame slots for this OSR. UnoptimizedFrameSlots()109 size_t UnoptimizedFrameSlots() { return stack_slot_count_; } 110 111 // Returns the environment index of the first stack slot. FirstStackSlotIndex(int parameter_count)112 static int FirstStackSlotIndex(int parameter_count) { 113 // n.b. unlike Crankshaft, TurboFan environments do not contain the context. 114 return 1 + parameter_count; // receiver + params 115 } 116 117 private: 118 size_t parameter_count_; 119 size_t stack_slot_count_; 120 }; 121 122 } // namespace compiler 123 } // namespace internal 124 } // namespace v8 125 126 #endif // V8_COMPILER_OSR_H_ 127