[ARM] GlobalISel: Fix stack-use-after-scope bug.
[ARM] GlobalISel: Fix stack-use-after-scope bug.

Summary:
Lifetime extension wasn't triggered on the result of BuildMI because the
reference was non-const. However, instead of adding a const, I've
removed the reference entirely as RVO should kick in anyway.

Reviewers: rovka, bkramer

Reviewed By: bkramer

Subscribers: aemerson, rengolin, dberris, llvm-commits, kristof.beyls

Differential Revision: https://reviews.llvm.org/D29124

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@293059 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,llvm-mirror/llvm