[Build Speed] PCH Test

[csarofeen]

Extracted the precompiled header part of #5747 to see what it would do in isolation.

Precompiled Header (PCH) Build Optimization for nvFuser

What It Does

Precompiled Headers (PCH) pre-parse frequently-included header files once and cache the result, eliminating redundant parsing across hundreds of source files.

This branch adds:

• PCH for 10 key nvFuser headers (polymorphic_value.h, type_traits.h, ir/base_nodes.h, etc.)
• Shared PCH across 20+ test targets (prevents redundant PCH compilation)

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Build Time Results

Compiler	Baseline	With PCH	Wall-clock Improvement
GCC	20m 51s	17m 6s	18% faster
Clang	20m 43s	8m 48s	57% faster

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CPU Time Results

Compiler	Baseline	With PCH	CPU Time Reduction
GCC	231 min	185 min	20% less work
Clang	232 min	97 min	58% less work

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Key Takeaway

PCH is a low-risk, high-impact optimization that can be merged independently. Clang users see the largest benefit (57% faster builds), while GCC users still gain a meaningful 18% improvement.

[csarofeen]

!test

[csarofeen]

CC @jacobhinkle

[github-actions]

Description

• Add Precompiled Headers (PCH) for top 10 nvFuser headers to reduce build time by ~50%

• Enable shared PCH across test targets to prevent redundant compilation

• Achieve 18% faster builds for GCC and 57% for Clang users

• Fix Clang unused-private-field warnings with [[maybe_unused]] attributes

Changes walkthrough

	Relevant files
Bug fix	symmetric_tensor.h Fix Clang unused private field warnings                                    csrc/multidevice/symmetric_tensor.h Add [[maybe_unused]] attributes to private fields mcast_handle_, cu_dev_, mc_ptr_, mc_base_ptr_, exporter_rank_, peer_fd_ Fix Clang unused-private-field warnings for unused private members +5/-5
Enhancement	CMakeLists.txt Add PCH optimization for build speed                                          CMakeLists.txt Add PCH configuration for top 10 nvFuser headers by parse time (polymorphic_value.h, type_traits.h, etc.) Enable PCH by default for Release builds with NVFUSER_USE_POLYMORPHIC_PCH option Implement shared PCH across test targets to avoid redundant compilation First test target creates PCH, subsequent targets reuse via REUSE_FROM +57/-0

PR Reviewer Guide

Here are some key observations to aid the review process:

🧪 No relevant tests

🔒 No security concerns identified

⚡ Recommended focus areas for review

Missing Validation The [[maybe_unused]] attributes were added to member variables (mcast_handle_, cu_dev_, mc_base_ptr_, exporter_rank_, peer_fd_) but there's no explanation or validation that these changes don't affect functionality. These appear to be CUDA-related variables whose usage should be verified. [[maybe_unused]] CUmemGenericAllocationHandle mcast_handle_{}; [[maybe_unused]] CUdevice cu_dev_{}; void* mc_ptr_{nullptr}; [[maybe_unused]] CUdeviceptr mc_base_ptr_{0}; [[maybe_unused]] int exporter_rank_{-1}; [[maybe_unused]] int peer_fd_{-1}; PCH Configuration Robustness The PCH implementation relies on global property tracking for test targets and assumes consistent header availability. Need to verify that all 10 specified header files exist and are accessible in all build environments, and that the global property mechanism works correctly across different build configurations. if(NVFUSER_USE_POLYMORPHIC_PCH) get_property(NVFUSER_TEST_PCH_TARGET GLOBAL PROPERTY NVFUSER_TEST_PCH_TARGET) if(NOT NVFUSER_TEST_PCH_TARGET) # First test target: create the PCH with top 10 nvFuser headers message(STATUS "Creating shared test PCH on target: ${TEST_NAME}") target_precompile_headers(${TEST_NAME} PRIVATE "${NVFUSER_SRCS_DIR}/polymorphic_value.h" "${NVFUSER_ROOT}/lib/dynamic_type/src/dynamic_type/type_traits.h" "${NVFUSER_SRCS_DIR}/ir/base_nodes.h" "${NVFUSER_SRCS_DIR}/scheduler/tools/abstract_tensor.h" "${NVFUSER_SRCS_DIR}/type.h" "${NVFUSER_SRCS_DIR}/ir/container.h" "${NVFUSER_SRCS_DIR}/serde/fusion_cache_generated.h" "${NVFUSER_SRCS_DIR}/iter_visitor.h" "${NVFUSER_SRCS_DIR}/ir/internal_nodes.h" "${NVFUSER_SRCS_DIR}/ir/interface_nodes.h" ) set_property(GLOBAL PROPERTY NVFUSER_TEST_PCH_TARGET ${TEST_NAME}) else() # Subsequent test targets: reuse existing PCH target_precompile_headers(${TEST_NAME} REUSE_FROM ${NVFUSER_TEST_PCH_TARGET}) endif() endif()