If you gave clang the options `--target=arm-pc-windows-msvc` and
`-march=armv8-a+crypto` together, the crypto extension would not be
enabled in the compilation, and you'd see the following warning
message suggesting that the 'armv8-a' had been ignored:
clang: warning: ignoring extension 'crypto' because the 'armv7-a' architecture does not support it [-Winvalid-command-line-argument]
This happens because Triple::getARMCPUForArch(), for the Win32 OS,
unconditionally returns "cortex-a9" (an Armv7 CPU) regardless of
MArch, which overrides the architecture setting on the command line.
I don't think that the combination of Windows and AArch32 _should_
unconditionally outlaw the use of the crypto extension. MSVC itself
doesn't think so: you can perfectly well compile Thumb crypto code
using its AArch32-targeted compiler.
All the other default CPUs in the same switch statement are
conditional on a particular MArch setting; this is the only one that
returns a particular CPU _regardless_ of MArch. So I've fixed this one
by adding a condition, so that if you ask for an architecture *above*
v7, the default of Cortex-A9 no longer overrides it.
Reviewed By: mstorsjo
Differential Revision: https://reviews.llvm.org/D100937
Simon Tatham