Fix assert about using an undefined physical register in machine instruction verify pass. Following is the error info. The reason is that register flag undef is missing when doing transformation from If Conversion Pass.
llc -verify-machineinstrs llvm/test/CodeGen/PowerPC/zero-not-run.ll
Bad machine code: Using an undefined physical register - function: func_65 - basic block: %bb.0 entry (0x10024740738) - instruction: BCLR killed $cr5lt, implicit $lr8, implicit $rm, implicit undef $x3 - operand 0: killed $cr5lt LLVM ERROR: Found 1 machine code errors.
There are other existing testcases that can show similar issues too. So I add -verify-machineinstrs option to open verifying.
@hfinkel could you please have a look since the last change is related to your part.