[spirv] Fix the entry block to start with OpLabel

Each basic block in SPIR-V must start with an OpLabel instruction.
We don't support control flow yet, so this CL just makes sure that
the entry block follows this rule and is valid.

PiperOrigin-RevId: 265718841

1 files changed, 2 insertions, 0 deletions

diff --git a/mlir/lib/Dialect/SPIRV/Serialization/Serializer.cpp b/mlir/lib/Dialect/SPIRV/Serialization/Serializer.cpp
index 03973db0d95..43a1d08cf6c 100644
--- a/mlir/lib/Dialect/SPIRV/Serialization/Serializer.cpp
+++ b/mlir/lib/Dialect/SPIRV/Serialization/Serializer.cpp
@@ -543,6 +543,8 @@ LogicalResult Serializer::processFuncOp(FuncOp op) {
   }
 
   for (auto &b : op) {
+    // TODO(antiagainst): support basic blocks and control flow properly.
+    encodeInstructionInto(functions, spirv::Opcode::OpLabel, {getNextID()});
     for (auto &op : b) {
       if (failed(processOperation(&op))) {
         return failure();