Fix assert about using an undefined physical register in machine instruction verify pass.
The reason is that register flag undef is missing when doing transformation from If Conversion Pass.
```
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 also other existing testcases with same issue. So I add -verify-machineinstrs option to open verifying.
Differential Revision: https://reviews.llvm.org/D55408
llvm-svn: 348566
Summary: Conditional returns were not taken into consideration at all. Implement them by turning them into jumps and normal returns. This means there is a slightly higher performance penalty for conditional returns, but this is the best we can do, and it still disturbs little of the rest.
Reviewers: dberris, echristo
Subscribers: sanjoy, nemanjai, hiraditya, kbarton, llvm-commits
Differential Revision: https://reviews.llvm.org/D38102
llvm-svn: 314005
Zi Xuan Wu