[Alignment] fix dubious min function alignment

Summary:
This was discovered while introducing the llvm::Align type.
The original setMinFunctionAlignment used to take alignment as log2, looking at the comment it seems like instructions are to be 2-bytes aligned and not 4-bytes aligned.

Reviewers: uweigand

Subscribers: hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D67271

llvm-svn: 371204

llvm/lib/Target/SystemZ/SystemZISelLowering.cpp

@@ -120,7 +120,7 @@ SystemZTargetLowering::SystemZTargetLowering(const TargetMachine &TM,
   setBooleanVectorContents(ZeroOrNegativeOneBooleanContent);
 
   // Instructions are strings of 2-byte aligned 2-byte values.
-  setMinFunctionAlignment(llvm::Align(4));
+  setMinFunctionAlignment(llvm::Align(2));
   // For performance reasons we prefer 16-byte alignment.
   setPrefFunctionLogAlignment(4);