[MSan] Don't create zero offsets in getShadowPtrForArgument(). NFC
[MSan] Don't create zero offsets in getShadowPtrForArgument(). NFC

For MSan instrumentation with MS.ParamTLS and MS.ParamOriginTLS being
TLS variables, the CreateAdd() with ArgOffset==0 is a no-op, because
the compiler is able to fold the addition of 0.

But for KMSAN, which receives ParamTLS and ParamOriginTLS from a call
to the runtime library, this introduces a stray instruction which
complicates reading/testing the IR.

Differential revision: https://reviews.llvm.org/D44514



git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@327829 91177308-0d34-0410-b5e6-96231b3b80d8

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