GlobalISel: Fix defined register of invariant.start (#125664)

In contrast to SelectionDAG, GlobalISel created a new virtual register
for the return value of invariant.start, leaving subsequent users of the
invariant.start value with an undefined reference.
A minimal example:
```
  %tmp = alloca i32, align 4, addrspace(5)
  %tmpI = call ptr @llvm.invariant.start.p5(i64 4, ptr addrspace(5) %tmp) #3
  call void @llvm.invariant.end.p5(ptr %tmpI, i64 4, ptr addrspace(5) %tmp) #3
  store i32 %i, ptr %tmpI, align 4
```
Although the return value of invariant.start might not be intended for
any use beyond invariant.end (the fuzzer might not have created a
sensible situation here), an implicit definition of the corresponding
virtual register avoids a segfault in the target instruction selector
later.

This LLVM defect was identified via the AMD Fuzzing project.

0 files changed, 0 insertions, 0 deletions