[WebAssembly] Initial support for reference type externref in clang

This patch introduces a new type __externref_t that denotes a WebAssembly opaque
reference type. It also implements builtin __builtin_wasm_ref_null_extern(),
that returns a null value of __externref_t. This lays the ground work
for further builtins and reference types.

Reviewed By: aaron.ballman

Differential Revision: https://reviews.llvm.org/D122215

1 files changed, 10 insertions, 0 deletions

diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp b/llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp
index 630c786..c10f070 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp
@@ -16,6 +16,7 @@
 #include "TargetInfo/WebAssemblyTargetInfo.h"
 #include "Utils/WebAssemblyUtilities.h"
 #include "WebAssembly.h"
+#include "WebAssemblyISelLowering.h"
 #include "WebAssemblyMachineFunctionInfo.h"
 #include "WebAssemblyTargetObjectFile.h"
 #include "WebAssemblyTargetTransformInfo.h"
@@ -464,6 +465,15 @@ void WebAssemblyPassConfig::addIRPasses() {
 }
 
 void WebAssemblyPassConfig::addISelPrepare() {
+  WebAssemblyTargetMachine *WasmTM =
+      static_cast<WebAssemblyTargetMachine *>(TM);
+  const WebAssemblySubtarget *Subtarget =
+      WasmTM->getSubtargetImpl(std::string(WasmTM->getTargetCPU()),
+                               std::string(WasmTM->getTargetFeatureString()));
+  if (Subtarget->hasReferenceTypes()) {
+    // We need to remove allocas for reference types
+    addPass(createPromoteMemoryToRegisterPass(true));
+  }
   // Lower atomics and TLS if necessary
   addPass(new CoalesceFeaturesAndStripAtomics(&getWebAssemblyTargetMachine()));