Reapply #5344

[wujingyue]

It got accidentally reverted by #5328

[wujingyue]

!test

[github-actions]

Description

• Fix signed-unsigned comparison in tensor shape inference

• Enable Host IR JIT as runtime via EnableOption

• Remove compile-time NVFUSER_HOST_IR_JIT flag

• Update docs on Host IR JIT runtime configuration

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Changes walkthrough 📝

	Relevant files
Bug fix	1 files jit.cpp Fix signed-unsigned size comparison                                            +2/-2
Enhancement	4 files options.cpp Add HostIrJit to enable options                                                    +1/-0      fusion_kernel_runtime.cpp Use EnableOption for Host IR backend selection                      +15/-18  options.h Add HostIrJit enable option                                                            +1/-0      fusion_kernel_runtime.h Conditionally include HostIrJit headers                                    +9/-12
Tests	2 files test_host_ir_integration.cpp Enable HostIrJit in integration tests                                        +1/-0      test_host_ir_jit.cpp Initialize HostIrJit in test fixture                                          +9/-4
Configuration changes	2 files utils.py Remove build_with_host_ir_jit flag                                              +0/-11    CMakeLists.txt Remove NVFUSER_HOST_IR_JIT option                                                +35/-45
Documentation	1 files host_ir_jit.md Update Host IR JIT configuration docs                                        +11/-14

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PR Reviewer Guide 🔍

Here are some key observations to aid the review process:

🧪 PR contains tests

⚡ Recommended focus areas for review Possible Null Pointer Dereference The code checks for hij_ and hie_ being non-null in isCompiled(), but does not validate their initialization before use in runWithInputs(), which could lead to a null pointer dereference if neither is initialized. KernelArgumentHolder outputs; if (hij_ != nullptr) { outputs = hij_->runWithInputs(args); } else if (hie_ != nullptr) { outputs = hie_->runWithInputs(args); } else { NVF_THROW("Neither Host IR JIT or Host IR Evaluator are initialized."); } Inconsistent State Handling The getHostIrContainer() method assumes either hij_ or hie_ is valid based on EnableOption::HostIrJit, but does not handle the case where both could be null, potentially leading to undefined behavior. if (isOptionEnabled(EnableOption::HostIrJit)) { NVF_ERROR(hij_ != nullptr, "Host IR JIT is not initialized"); return hij_->container(); } else { NVF_ERROR(hie_ != nullptr, "Host IR Evaluator is not initialized"); return hie_->container(); } Use of Non-Standard Function The use of std::ssize() may not be supported in all standard library implementations, potentially causing compilation issues on certain platforms. NVF_ERROR_EQ(std::ssize(sizes), logical_ndims); NVF_ERROR_EQ(std::ssize(strides), logical_ndims);