Assign variables with initial/default values (#14511)

To avoid maybe-uninitialized GCC warning
diff --git a/compiler/src/iree/compiler/Codegen/LLVMCPU/LLVMCPULowerToUKernels.cpp b/compiler/src/iree/compiler/Codegen/LLVMCPU/LLVMCPULowerToUKernels.cpp
index 8084aac..1079cac 100644
--- a/compiler/src/iree/compiler/Codegen/LLVMCPU/LLVMCPULowerToUKernels.cpp
+++ b/compiler/src/iree/compiler/Codegen/LLVMCPU/LLVMCPULowerToUKernels.cpp
@@ -397,6 +397,9 @@
     return IREE_UK_FLAG_QUERY_TILE_SIZES_OPERATION_MATMUL_BF16BF16F32;
   case IREE::LinalgExt::EncodingUser::MATMUL_BF16BF16BF16:
     return IREE_UK_FLAG_QUERY_TILE_SIZES_OPERATION_MATMUL_BF16BF16BF16;
+  default: // Unreachable.
+    assert(false);
+    return IREE_UK_FLAG_QUERY_TILE_SIZES_OPERATION_NONE;
   }
 }
 
@@ -408,6 +411,9 @@
     return IREE_UK_FLAG_QUERY_TILE_SIZES_OPERAND_ROLE_RHS;
   case IREE::LinalgExt::EncodingRole::RESULT:
     return IREE_UK_FLAG_QUERY_TILE_SIZES_OPERAND_ROLE_RESULT;
+  default: // Unreachable.
+    assert(false);
+    return IREE_UK_FLAG_QUERY_TILE_SIZES_OPERAND_ROLE_LHS;
   }
 }
 
diff --git a/compiler/src/iree/compiler/Codegen/LLVMCPU/LLVMCPUTensorPad.cpp b/compiler/src/iree/compiler/Codegen/LLVMCPU/LLVMCPUTensorPad.cpp
index 177d817..aa1f6fe 100644
--- a/compiler/src/iree/compiler/Codegen/LLVMCPU/LLVMCPUTensorPad.cpp
+++ b/compiler/src/iree/compiler/Codegen/LLVMCPU/LLVMCPUTensorPad.cpp
@@ -38,8 +38,8 @@
   auto funcOp = getOperation();
   // Preserve the innermost tensor.pad ops (i.e., pad for reduction dims), so we
   // can kick canonicalization patterns to fold outer tensor.pad ops away.
-  bool nofold;
-  utils::IteratorType targetIterType;
+  bool nofold = false;
+  utils::IteratorType targetIterType = utils::IteratorType::parallel;
   switch (option) {
   case LLVMCPUTensorPadOption::ParallelDims:
     LLVM_DEBUG(llvm::dbgs() << "padding parallel dims\n");
@@ -51,6 +51,9 @@
     targetIterType = utils::IteratorType::reduction;
     nofold = true;
     break;
+  default: // Unreachable.
+    assert(false);
+    break;
   };
   SmallVector<linalg::LinalgOp> candidates;
   funcOp.walk([&](linalg::LinalgOp op) { candidates.push_back(op); });
diff --git a/compiler/src/iree/compiler/ConstEval/Runtime.cpp b/compiler/src/iree/compiler/ConstEval/Runtime.cpp
index e49f9a9..967e503 100644
--- a/compiler/src/iree/compiler/ConstEval/Runtime.cpp
+++ b/compiler/src/iree/compiler/ConstEval/Runtime.cpp
@@ -219,7 +219,7 @@
     for (size_t i = 0; i < rank; ++i) {
       shape[i] = stShape[i];
     }
-    iree_hal_element_type_t elementType;
+    iree_hal_element_type_t elementType = IREE_HAL_ELEMENT_TYPE_NONE;
     if (failed(convertToElementType(loc, st.getElementType(), &elementType)))
       return failure();