[mlir][gpu] Fix another windows build issue

Fixes another Windows build failure (C4715) caused by
6ca1a09f03e8e940f306bea73efa935e4ee38173.

diff --git a/mlir/lib/Dialect/GPU/Transforms/LowerMemorySpaceAttributes.cpp b/mlir/lib/Dialect/GPU/Transforms/LowerMemorySpaceAttributes.cpp
index bb5fb06..40c2647 100644 (file)
--- a/mlir/lib/Dialect/GPU/Transforms/LowerMemorySpaceAttributes.cpp
+++ b/mlir/lib/Dialect/GPU/Transforms/LowerMemorySpaceAttributes.cpp
@@ -172,6 +172,8 @@ public:
           case AddressSpace::Private:
             return privateAddrSpace;
           }
+          llvm_unreachable("unknown address space enum value");
+          return 0;
         });
     RewritePatternSet patterns(context);
     populateMemorySpaceLoweringPatterns(typeConverter, patterns);