Use correct registers for "A" inline asm constraint
Summary:
In PR32594, inline assembly using the 'A' constraint on x86_64 causes
llvm to crash with a "Cannot select" stack trace. This is because
`X86TargetLowering::getRegForInlineAsmConstraint` hardcodes that 'A'
means the EAX and EDX registers.
However, on x86_64 it means the RAX and RDX registers, and on 16-bit
x86 (ia16?) it means the old AX and DX registers.
Add new register classes in `X86RegisterInfo.td` to support these
cases, and amend the logic in `getRegForInlineAsmConstraint` to cope
with different subtargets. Also add a test case, derived from
PR32594.
Reviewers: craig.topper, qcolombet, RKSimon, ab
Reviewed By: ab
Subscribers: ab, emaste, royger, llvm-commits
Differential Revision: https://reviews.llvm.org/D31902
This should fix crashes when using the 'A' constraint on amd64, for
example as it is being used in Xen.
Reported by: royger
MFC after: 3 days
86a34ce5a4