(reland) [GlobalISel] Diagnose inline assembly constraint lowering errors (#139049)
The initial patch (#135782 caused issues because it emits an error, and llc is sensitive to it.
It also caused compiler-rt/lib/scudo/standalone/tests/wrappers_cpp_test.cpp to fail.
Use warnings instead + reject lowering. That way, the fallback path is used without llc/clang returning a failure code.
If fallback isn't enabled then the warnings provide context as to why lowering failed.
Original commit description for #135782:
Instead of printing something to dbgs (which is not visible to all users),
emit a diagnostic like the DAG does. We still crash later because we fail to
select the inline assembly, but at least now users will know why it's crashing.
In a future patch we could also recover from the error like the DAG does, so the
lowering can keep going until it either crashes or gives a different error later.
llvm-project
534d221b - (reland) [GlobalISel] Diagnose inline assembly constraint lowering errors (#139049)
