[WebAssembly] Implement ref.null

This patch adds a new "heap type" operand kind to the WebAssembly MC
layer, used by ref.null. Currently the possible values are "extern" and
"func"; when typed function references come, though, this operand may be
a type index.

Note that the "heap type" production is still known as "refedtype" in
the draft proposal; changing its name in the spec is
ongoing (https://github.com/WebAssembly/reference-types/issues/123).

The register form of ref.null is still untested.

Differential Revision: https://reviews.llvm.org/D90608

1 files changed, 5 insertions, 0 deletions

diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyMCInstLower.cpp b/llvm/lib/Target/WebAssembly/WebAssemblyMCInstLower.cpp
index 7774a0d..09d1b96 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyMCInstLower.cpp
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyMCInstLower.cpp
@@ -271,6 +271,11 @@ void WebAssemblyMCInstLower::lower(const MachineInstr *MI,
                                          SmallVector<wasm::ValType, 4>());
             break;
           }
+        } else if (Info.OperandType == WebAssembly::OPERAND_HEAPTYPE) {
+          auto HT = static_cast<WebAssembly::HeapType>(MO.getImm());
+          assert(HT != WebAssembly::HeapType::Invalid);
+          // With typed function references, this will need a case for type
+          // index operands.  Otherwise, fall through.
         }
       }
       MCOp = MCOperand::createImm(MO.getImm());