[llvm-bugs] [Bug 43503] New: Crash during build when removing instruction sets

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=43503

            Bug ID: 43503
           Summary: Crash during build when removing instruction sets
           Product: clang
           Version: unspecified
          Hardware: Macintosh
                OS: MacOS X
            Status: NEW
          Severity: normal
          Priority: P
         Component: -New Bugs
          Assignee: unassignedclangbugs at nondot.org
          Reporter: rene.sugar at gmail.com
                CC: htmldeveloper at gmail.com, llvm-bugs at lists.llvm.org,
                    neeilans at live.com, richard-llvm at metafoo.co.uk

I tried modifying the code generation of the Homebrew LLVM formula to build
without instructions illegal on my computer's CPU.

The version of clang that came with Xcode runs...

clang --version
Apple LLVM version 10.0.1 (clang-1001.0.46.4)
Target: x86_64-apple-darwin18.5.0
Thread model: posix
InstalledDir:
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin

but, clang build via Homebrew is failing when trying to remove instruction sets
not supported by my computer's CPU.


Steps:

1. brew edit llvm

2. Add CMAKE_CXX_FLAGS to
/usr/local/Homebrew/Library/Taps/homebrew/homebrew-core/Formula/llvm.rb

https://github.com/Homebrew/homebrew-core/blob/master/Formula/llvm.rb

a) fails later

-DCMAKE_CXX_FLAGS:STRING='--target=x86_64-apple-darwin16.6.0\ -mno-sse4a\
-mno-sse4.2\ -mno-avx'

b) fails earlier

-DCMAKE_CXX_FLAGS:STRING='--target=x86_64-apple-darwin16.6.0\ -mno-sse\
-mno-sse2\ -mno-sse3\ -mno-ssse3\ -mno-sse4a\ -mno-sse4.1\ -mno-sse4.2\
-mno-avx'

3. brew install --build-from-source --verbose llvm

4. LLVM build fails in different places depending upon which instruction sets
are turned off.


Older MacBook Pro with the following capabilities:

https://github.com/Mysticial/FeatureDetector

./FeatureDetector_main
CPU Vendor String: GenuineIntel

CPU Vendor:
    AMD         = No
    Intel       = Yes

OS Features:
    OS AVX      = No
    OS AVX512   = No

Hardware Features:
    MMX         = Yes
    x64         = Yes
    ABM         = No
    RDRAND      = No
    BMI1        = No
    BMI2        = No
    ADX         = No
    MPX         = No
    PREFETCHWT1 = No

SIMD: 128-bit
    SSE         = Yes
    SSE2        = Yes
    SSE3        = Yes
    SSSE3       = Yes
    SSE4a       = No
    SSE4.1      = Yes
    SSE4.2      = No
    AES-NI      = No
    SHA         = No

SIMD: 256-bit
    AVX         = No
    XOP         = No
    FMA3        = No
    FMA4        = No
    AVX2        = No

SIMD: 512-bit
    AVX512-F    = No
    AVX512-CD   = No
    AVX512-PF   = No
    AVX512-ER   = No
    AVX512-VL   = No
    AVX512-BW   = No
    AVX512-DQ   = No
    AVX512-IFMA = No
    AVX512-VBMI = No

Summary:
    Safe to use AVX:     No
    Safe to use AVX512:  No


Just setting the following allows Homebrew LLVM to build but instructions
illegal on my computer's CPU are included causing a crash when trying to
compile the regex Python extension:

export MACOSX_DEPLOYMENT_TARGET=10.12
export CFLAGS=--target=x86_64-apple-darwin16.6.0

https://bitbucket.org/mrabarnett/mrab-regex/

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