jcai19 added inline comments.

================
Comment at: clang/lib/Driver/ToolChains/Arch/AArch64.cpp:217
+  // after -march. And while only using the the value of last -march, it
+  // includes all the options passed via -Wa,-march.
+  success = true;
----------------
joerg wrote:
> This comment is confusing. `-march` is a driver option and the GCC driver 
> will internally convert it into the equivalent of `-Wa,-march` before passing 
> the total command line to GNU as.
Thanks for the clarification! I haven't checked GCC implementation so the 
comment is likely not accurate. I did make the following observation from below 
command and its output. It seems all the -Wa.-march values passed (armv8.3-a 
and armv8.4a) showed up in COLLECT_AS_OPTIONS, as well as in 
COLLECT_GCC_OPTIONS. On the other hand, only the last value of -march 
(armv8.2-a) showed up in COLLECT_GCC_OPTIONS, and the -march value was placed 
before all the -Wa,-march values in COLLECT_GCC_OPTIONS. WDYT?

$ aarch64-linux-gnu-gcc -Wa,-march=armv8.1-a -march=armv8.2-a -march=armv8.3-a 
-Wa,-march=armv8.4-a -c foo.s -o gcc.o -###
Using built-in specs.
COLLECT_AS_OPTIONS='-march=armv8.1-a' '-march=armv8.4-a'
COLLECT_GCC=aarch64-linux-gnu-gcc
Target: aarch64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Debian 10.2.1-6+build2' 
--with-bugurl=file:///usr/share/doc/gcc-10/README.Bugs 
--enable-languages=c,ada,c++,go,d,fortran,objc,obj-c++,m2 --prefix=/usr 
--with-gcc-major-version-only --program-suffix=-10 --enable-shared 
--enable-linker-build-id --libexecdir=/usr/lib --without-included-gettext 
--enable-threads=posix --libdir=/usr/lib --enable-nls --with-sysroot=/ 
--enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes 
--with-default-libstdcxx-abi=new --enable-gnu-unique-object 
--disable-libquadmath --disable-libquadmath-support --enable-plugin 
--enable-default-pie --with-system-zlib --enable-libphobos-checking=release 
--without-target-system-zlib --enable-multiarch --enable-fix-cortex-a53-843419 
--disable-werror --enable-checking=release --build=x86_64-linux-gnu 
--host=x86_64-linux-gnu --target=aarch64-linux-gnu 
--program-prefix=aarch64-linux-gnu- --includedir=/usr/aarch64-linux-gnu/include 
--with-build-config=bootstrap-lto-lean --enable-link-mutex
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 10.2.1 20210110 (Debian 10.2.1-6+build2) 
COLLECT_GCC_OPTIONS='-march=armv8.3-a' '-c' '-o' 'gcc.o' '-mlittle-endian' 
'-mabi=lp64'
 /usr/lib/gcc-cross/aarch64-linux-gnu/10/../../../../aarch64-linux-gnu/bin/as 
-EL "-march=armv8.3-a" "-mabi=lp64" "-march=armv8.1-a" "-march=armv8.4-a" -o 
gcc.o foo.s
COMPILER_PATH=/usr/lib/gcc-cross/aarch64-linux-gnu/10/:/usr/lib/gcc-cross/aarch64-linux-gnu/10/:/usr/lib/gcc-cross/aarch64-linux-gnu/:/usr/lib/gcc-cross/aarch64-linux-gnu/10/:/usr/lib/gcc-cross/aarch64-linux-gnu/:/usr/lib/gcc-cross/aarch64-linux-gnu/10/../../../../aarch64-linux-gnu/bin/
LIBRARY_PATH=/usr/lib/gcc-cross/aarch64-linux-gnu/10/:/usr/lib/gcc-cross/aarch64-linux-gnu/10/../../../../aarch64-linux-gnu/lib/../lib/:/lib/aarch64-linux-gnu/:/lib/../lib/:/usr/lib/aarch64-linux-gnu/:/usr/lib/../lib/:/usr/lib/gcc-cross/aarch64-linux-gnu/10/../../../../aarch64-linux-gnu/lib/:/lib/:/usr/lib/
COLLECT_GCC_OPTIONS='-march=armv8.3-a' '-c' '-o' 'gcc.o' '-mlittle-endian' 
'-mabi=lp64'



Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D103184/new/

https://reviews.llvm.org/D103184

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