COMP: Remove hardcoded -march=corei7, -mtune=generic, and dead code

[hjmjohnson]

Remove architecture-specific compiler flags that are unnecessary or broken, and dead Intel ICC detection code. Closes #2634. Supersedes #6039.

What was removed and why

Removed	Reason
-march=corei7	Recent GCC removed corei7 as an -march option (#2634). Targeted Nehalem (2008).
-mtune=generic	This is the compiler default when no -mtune is specified — always a no-op.
Intel ICC detection (icc/icpc)	ICC was EOL 2023, replaced by ICX which identifies as Clang. The detection block only set InstructionSetOptimizationFlags to empty — same as the default.

No architecture flags are set by default, ensuring maximum redistributability for pip wheels, Docker images, and hardware translation (Rosetta, QEMU). Users building for local performance should add -march=native via CMAKE_C_FLAGS or CMakeUserPresets.json.

Added a CMake comment cautioning that -march=native on AVX-512 CPUs should be paired with -mprefer-vector-width=256 to avoid Intel frequency throttling.

[greptile-apps]

Greptile Summary

Removes the -march=corei7 and -mtune=generic compiler flags from the non-MSVC x86/x86_64 path in check_compiler_optimization_flags, and deletes the now-redundant Intel ICC detection block (both branches of which already set InstructionSetOptimizationFlags to empty and were then unconditionally overwritten). The change is correct: -march=corei7 has been dropped from recent GCC releases, and -mtune=generic was always the compiler default, making both flags either harmful or no-ops.

Confidence Score: 5/5

Safe to merge — removes a build-breaking flag with no functional regression.

The only remaining finding is a P2 style suggestion about two empty placeholder variables. All logic changes are correct and well-documented; no new flags, no behaviour change for MSVC or non-x86 paths.

No files require special attention.

Important Files Changed

Filename	Overview
CMake/ITKSetStandardCompilerFlags.cmake	Removes -march=corei7 and -mtune=generic from non-MSVC x86/x86_64 GCC/Clang paths, deletes now-dead ICC detection code, and documents the rationale inline. Logic is correct; c_flags/cxx_flags placeholders remain but are harmless.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[check_compiler_optimization_flags] --> B{x86_64 / AMD64?}
    B -- No --> Z[c_and_cxx_flags = empty]
    B -- Yes --> C{MSVC?}
    C -- Yes --> D[check_avx_flags\n+ /arch:SSE /arch:SSE2 if 32-bit]
    C -- No --> E{NOT EMSCRIPTEN\nOR WASI?}
    E -- Yes --> F["InstructionSetOptimizationFlags = empty\n(was: -march=corei7 -mtune=generic)\n(was also: dead ICC detection)"]
    E -- No --> Z
    D --> G[c_and_cxx_flags = InstructionSetOptimizationFlags]
    F --> G
    G --> H[check_c_compiler_flags\ncheck_cxx_compiler_flags]
    H --> I[Return c / cxx optimization flags to caller]

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_{Reviews (1): Last reviewed commit: "COMP: Remove hardcoded -march=corei7 and..." | Re-trigger Greptile}

[blowekamp]

I agree with this packager need specific flags ( and it can be tedious to disable hard coded one), and local developers using the native architecture is a good option for local executables.

[hjmjohnson]

Close, but some changes need addressing.