[llvm-bugs] [Bug 38629] New: -mfpu=neon overrides +crypto part of -march=armv8-a+crypto

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=38629

            Bug ID: 38629
           Summary: -mfpu=neon overrides +crypto part of
                    -march=armv8-a+crypto
           Product: clang
           Version: 7.0
          Hardware: PC
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Driver
          Assignee: unassignedclangbugs at nondot.org
          Reporter: lennox at cs.columbia.edu
                CC: llvm-bugs at lists.llvm.org

Passing -mfpu=neon on the clang command line for arm32 (specifically with the
target triple armv7-none-linux-androideabi) disables the __ARM_FEATURE_CRYPTO
feature which would normally be enabled by -march=armv8+crypto, even though the
armv8 part of the flag takes effect, even if the -march flag is specified
later.

This is particularly problematic because -mfpu=neon tends to get added
automatically by Android build procedures when vector support is needed.

E.g.:

$ clang -target armv7-none-linux-androideabi -mfloat-abi=softfp -E -dM -x c
/dev/null | egrep 'CRYPTO|ARM_ARCH '
#define __ARM_ARCH 7

$ clang -target armv7-none-linux-androideabi -mfloat-abi=softfp
-march=armv8+crypto -E -dM -x c /dev/null | egrep 'CRYPTO|ARM_ARCH '
#define __ARM_ARCH 8
#define __ARM_FEATURE_CRYPTO 1

$ clang -target armv7-none-linux-androideabi -mfloat-abi=softfp -mfpu=neon
-march=armv8+crypto -E -dM -x c /dev/null | egrep 'CRYPTO|ARM_ARCH '
#define __ARM_ARCH 8

$ clang -target armv7-none-linux-androideabi -v
Android (4751641 based on r328903) clang version 7.0.2
(https://android.googlesource.com/toolchain/clang
003100370607242ddd5815e4a043907ea9004281)
(https://android.googlesource.com/toolchain/llvm
1d739ffb0366421d383e04ff80ec2ee591315116) (based on LLVM 7.0.2svn)
Target: armv7-none-linux-android
Thread model: posix
InstalledDir:
/Users/jonathan/Android/android-ndk-r18-beta1/toolchains/llvm/prebuilt/darwin-x86_64/bin

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