Fix a bug where we would corrupt the offset when evaluating a non-constant GEP.
Fix a bug where we would corrupt the offset when evaluating
a non-constant GEP.

I don't have any test case that demonstrates this, Nadav (indirectly)
pointed this out in code review. I'm not sure how possible it is to
contrive a test case for the current users of this code that triggers
the bad issue sadly.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@189188 91177308-0d34-0410-b5e6-96231b3b80d8

chubbymaggie/asap,chubbymaggie/asap,llvm-mirror/llvm,dslab-epfl/asap,llvm-mirror/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,dslab-epfl/asap,apple/swift-llvm,apple/swift-llvm,chubbymaggie/asap,GPUOpen-Drivers/llvm,apple/swift-llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,dslab-epfl/asap,llvm-mirror/llvm,dslab-epfl/asap,chubbymaggie/asap,llvm-mirror/llvm,apple/swift-llvm,dslab-epfl/asap,apple/swift-llvm,dslab-epfl/asap,GPUOpen-Drivers/llvm,apple/swift-llvm,chubbymaggie/asap,llvm-mirror/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,dslab-epfl/asap,chubbymaggie/asap,apple/swift-llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm