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Bug 1166711 part 0.5 - Add a big comment to explain Recover instructions. r=bhackett

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Nicolas B. Pierron 2015-06-11 14:30:31 +02:00
parent 7afe03e95a
commit 20eacb93b2
1 changed files with 37 additions and 0 deletions
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37
js/src/jit/Recover.h
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@ -19,6 +19,43 @@ struct JSContext;
namespace js {
namespace jit {
// This file contains all recover instructions.
//
// A recover instruction is an equivalent of a MIR instruction which is executed
// before the reconstruction of a baseline frame. Recover instructions are used
// by resume points to fill the value which are not produced by the code
// compiled by IonMonkey. For example, if a value is optimized away by
// IonMonkey, but required by Baseline, then we should have a recover
// instruction to fill the missing baseline frame slot.
//
// Recover instructions are executed either during a bailout, or under a call
// when the stack frame is introspected. If the stack is introspected, then any
// use of recover instruction must lead to an invalidation of the code.
//
// For each MIR instruction where |canRecoverOnBailout| might return true, we
// have a RInstruction of the same name.
//
// Recover instructions are encoded by code generator into a compact buffer
// (RecoverWriter). The MIR instruction method |writeRecoverData| should write a
// tag in the |CompactBufferWriter| which is used by
// |RInstruction::readRecoverData| to dispatch to the right Recover
// instruction. Then |writeRecoverData| writes any local fields which are
// necessary for the execution of the |recover| method. These fields are decoded
// by the Recover instruction constructor which has a |CompactBufferReader| as
// argument. The constructor of the Recover instruction should follow the same
// sequence as the |writeRecoverData| method of the MIR instruction.
//
// Recover instructions are decoded by the |SnapshotIterator| (RecoverReader),
// which is given as argument of the |recover| methods, in order to read the
// operands. The number of operands read should be the same as the result of
// |numOperands|, which corresponds to the number of operands of the MIR
// instruction. Operands should be decoded in the same order as the operands of
// the MIR instruction.
//
// The result of the |recover| method should either be a failure, or a value
// stored on the |SnapshotIterator|, by using the |storeInstructionResult|
// method.
#define RECOVER_OPCODE_LIST(_) \
_(ResumePoint) \
_(BitNot) \