void CallFrameShuffleData::setupCalleeSaveRegisters(CodeBlock* codeBlock) { RegisterSet calleeSaveRegisters { RegisterSet::vmCalleeSaveRegisters() }; RegisterAtOffsetList* registerSaveLocations = codeBlock->calleeSaveRegisters(); for (size_t i = 0; i < registerSaveLocations->size(); ++i) { RegisterAtOffset entry { registerSaveLocations->at(i) }; if (!calleeSaveRegisters.get(entry.reg())) continue; VirtualRegister saveSlot { entry.offsetAsIndex() }; registers[entry.reg()] = ValueRecovery::displacedInJSStack(saveSlot, DataFormatJS); } for (Reg reg = Reg::first(); reg <= Reg::last(); reg = reg.next()) { if (!calleeSaveRegisters.get(reg)) continue; if (registers[reg]) continue; registers[reg] = ValueRecovery::inRegister(reg, DataFormatJS); } }
SUPPRESS_ASAN void* prepareOSREntry(ExecState* exec, CodeBlock* codeBlock, unsigned bytecodeIndex) { ASSERT(JITCode::isOptimizingJIT(codeBlock->jitType())); ASSERT(codeBlock->alternative()); ASSERT(codeBlock->alternative()->jitType() == JITCode::BaselineJIT); ASSERT(!codeBlock->jitCodeMap()); if (!Options::useOSREntryToDFG()) return 0; if (Options::verboseOSR()) { dataLog( "DFG OSR in ", *codeBlock->alternative(), " -> ", *codeBlock, " from bc#", bytecodeIndex, "\n"); } VM* vm = &exec->vm(); sanitizeStackForVM(vm); if (bytecodeIndex) codeBlock->ownerScriptExecutable()->setDidTryToEnterInLoop(true); if (codeBlock->jitType() != JITCode::DFGJIT) { RELEASE_ASSERT(codeBlock->jitType() == JITCode::FTLJIT); // When will this happen? We could have: // // - An exit from the FTL JIT into the baseline JIT followed by an attempt // to reenter. We're fine with allowing this to fail. If it happens // enough we'll just reoptimize. It basically means that the OSR exit cost // us dearly and so reoptimizing is the right thing to do. // // - We have recursive code with hot loops. Consider that foo has a hot loop // that calls itself. We have two foo's on the stack, lets call them foo1 // and foo2, with foo1 having called foo2 from foo's hot loop. foo2 gets // optimized all the way into the FTL. Then it returns into foo1, and then // foo1 wants to get optimized. It might reach this conclusion from its // hot loop and attempt to OSR enter. And we'll tell it that it can't. It // might be worth addressing this case, but I just think this case will // be super rare. For now, if it does happen, it'll cause some compilation // thrashing. if (Options::verboseOSR()) dataLog(" OSR failed because the target code block is not DFG.\n"); return 0; } JITCode* jitCode = codeBlock->jitCode()->dfg(); OSREntryData* entry = jitCode->osrEntryDataForBytecodeIndex(bytecodeIndex); if (!entry) { if (Options::verboseOSR()) dataLogF(" OSR failed because the entrypoint was optimized out.\n"); return 0; } ASSERT(entry->m_bytecodeIndex == bytecodeIndex); // The code below checks if it is safe to perform OSR entry. It may find // that it is unsafe to do so, for any number of reasons, which are documented // below. If the code decides not to OSR then it returns 0, and it's the caller's // responsibility to patch up the state in such a way as to ensure that it's // both safe and efficient to continue executing baseline code for now. This // should almost certainly include calling either codeBlock->optimizeAfterWarmUp() // or codeBlock->dontOptimizeAnytimeSoon(). // 1) Verify predictions. If the predictions are inconsistent with the actual // values, then OSR entry is not possible at this time. It's tempting to // assume that we could somehow avoid this case. We can certainly avoid it // for first-time loop OSR - that is, OSR into a CodeBlock that we have just // compiled. Then we are almost guaranteed that all of the predictions will // check out. It would be pretty easy to make that a hard guarantee. But // then there would still be the case where two call frames with the same // baseline CodeBlock are on the stack at the same time. The top one // triggers compilation and OSR. In that case, we may no longer have // accurate value profiles for the one deeper in the stack. Hence, when we // pop into the CodeBlock that is deeper on the stack, we might OSR and // realize that the predictions are wrong. Probably, in most cases, this is // just an anomaly in the sense that the older CodeBlock simply went off // into a less-likely path. So, the wisest course of action is to simply not // OSR at this time. for (size_t argument = 0; argument < entry->m_expectedValues.numberOfArguments(); ++argument) { if (argument >= exec->argumentCountIncludingThis()) { if (Options::verboseOSR()) { dataLogF(" OSR failed because argument %zu was not passed, expected ", argument); entry->m_expectedValues.argument(argument).dump(WTF::dataFile()); dataLogF(".\n"); } return 0; } JSValue value; if (!argument) value = exec->thisValue(); else value = exec->argument(argument - 1); if (!entry->m_expectedValues.argument(argument).validate(value)) { if (Options::verboseOSR()) { dataLog( " OSR failed because argument ", argument, " is ", value, ", expected ", entry->m_expectedValues.argument(argument), ".\n"); } return 0; } } for (size_t local = 0; local < entry->m_expectedValues.numberOfLocals(); ++local) { int localOffset = virtualRegisterForLocal(local).offset(); if (entry->m_localsForcedDouble.get(local)) { if (!exec->registers()[localOffset].asanUnsafeJSValue().isNumber()) { if (Options::verboseOSR()) { dataLog( " OSR failed because variable ", localOffset, " is ", exec->registers()[localOffset].asanUnsafeJSValue(), ", expected number.\n"); } return 0; } continue; } if (entry->m_localsForcedAnyInt.get(local)) { if (!exec->registers()[localOffset].asanUnsafeJSValue().isAnyInt()) { if (Options::verboseOSR()) { dataLog( " OSR failed because variable ", localOffset, " is ", exec->registers()[localOffset].asanUnsafeJSValue(), ", expected ", "machine int.\n"); } return 0; } continue; } if (!entry->m_expectedValues.local(local).validate(exec->registers()[localOffset].asanUnsafeJSValue())) { if (Options::verboseOSR()) { dataLog( " OSR failed because variable ", localOffset, " is ", exec->registers()[localOffset].asanUnsafeJSValue(), ", expected ", entry->m_expectedValues.local(local), ".\n"); } return 0; } } // 2) Check the stack height. The DFG JIT may require a taller stack than the // baseline JIT, in some cases. If we can't grow the stack, then don't do // OSR right now. That's the only option we have unless we want basic block // boundaries to start throwing RangeErrors. Although that would be possible, // it seems silly: you'd be diverting the program to error handling when it // would have otherwise just kept running albeit less quickly. unsigned frameSizeForCheck = jitCode->common.requiredRegisterCountForExecutionAndExit(); if (!vm->interpreter->stack().ensureCapacityFor(&exec->registers()[virtualRegisterForLocal(frameSizeForCheck - 1).offset()])) { if (Options::verboseOSR()) dataLogF(" OSR failed because stack growth failed.\n"); return 0; } if (Options::verboseOSR()) dataLogF(" OSR should succeed.\n"); // At this point we're committed to entering. We will do some work to set things up, // but we also rely on our caller recognizing that when we return a non-null pointer, // that means that we're already past the point of no return and we must succeed at // entering. // 3) Set up the data in the scratch buffer and perform data format conversions. unsigned frameSize = jitCode->common.frameRegisterCount; unsigned baselineFrameSize = entry->m_expectedValues.numberOfLocals(); unsigned maxFrameSize = std::max(frameSize, baselineFrameSize); Register* scratch = bitwise_cast<Register*>(vm->scratchBufferForSize(sizeof(Register) * (2 + JSStack::CallFrameHeaderSize + maxFrameSize))->dataBuffer()); *bitwise_cast<size_t*>(scratch + 0) = frameSize; void* targetPC = codeBlock->jitCode()->executableAddressAtOffset(entry->m_machineCodeOffset); if (Options::verboseOSR()) dataLogF(" OSR using target PC %p.\n", targetPC); RELEASE_ASSERT(targetPC); *bitwise_cast<void**>(scratch + 1) = targetPC; Register* pivot = scratch + 2 + JSStack::CallFrameHeaderSize; for (int index = -JSStack::CallFrameHeaderSize; index < static_cast<int>(baselineFrameSize); ++index) { VirtualRegister reg(-1 - index); if (reg.isLocal()) { if (entry->m_localsForcedDouble.get(reg.toLocal())) { *bitwise_cast<double*>(pivot + index) = exec->registers()[reg.offset()].asanUnsafeJSValue().asNumber(); continue; } if (entry->m_localsForcedAnyInt.get(reg.toLocal())) { *bitwise_cast<int64_t*>(pivot + index) = exec->registers()[reg.offset()].asanUnsafeJSValue().asAnyInt() << JSValue::int52ShiftAmount; continue; } } pivot[index] = exec->registers()[reg.offset()].asanUnsafeJSValue(); } // 4) Reshuffle those registers that need reshuffling. Vector<JSValue> temporaryLocals(entry->m_reshufflings.size()); for (unsigned i = entry->m_reshufflings.size(); i--;) temporaryLocals[i] = pivot[VirtualRegister(entry->m_reshufflings[i].fromOffset).toLocal()].asanUnsafeJSValue(); for (unsigned i = entry->m_reshufflings.size(); i--;) pivot[VirtualRegister(entry->m_reshufflings[i].toOffset).toLocal()] = temporaryLocals[i]; // 5) Clear those parts of the call frame that the DFG ain't using. This helps GC on // some programs by eliminating some stale pointer pathologies. for (unsigned i = frameSize; i--;) { if (entry->m_machineStackUsed.get(i)) continue; pivot[i] = JSValue(); } // 6) Copy our callee saves to buffer. #if NUMBER_OF_CALLEE_SAVES_REGISTERS > 0 RegisterAtOffsetList* registerSaveLocations = codeBlock->calleeSaveRegisters(); RegisterAtOffsetList* allCalleeSaves = vm->getAllCalleeSaveRegisterOffsets(); RegisterSet dontSaveRegisters = RegisterSet(RegisterSet::stackRegisters(), RegisterSet::allFPRs()); unsigned registerCount = registerSaveLocations->size(); VMEntryRecord* record = vmEntryRecord(vm->topVMEntryFrame); for (unsigned i = 0; i < registerCount; i++) { RegisterAtOffset currentEntry = registerSaveLocations->at(i); if (dontSaveRegisters.get(currentEntry.reg())) continue; RegisterAtOffset* calleeSavesEntry = allCalleeSaves->find(currentEntry.reg()); *(bitwise_cast<intptr_t*>(pivot - 1) - currentEntry.offsetAsIndex()) = record->calleeSaveRegistersBuffer[calleeSavesEntry->offsetAsIndex()]; } #endif // 7) Fix the call frame to have the right code block. *bitwise_cast<CodeBlock**>(pivot - 1 - JSStack::CodeBlock) = codeBlock; if (Options::verboseOSR()) dataLogF(" OSR returning data buffer %p.\n", scratch); return scratch; }