[WebAssembly] Disable reference types in generic CPU

[aheejin]

#80923 newly enabled multivalue and reference-types in the generic CPU.
But enabling reference-types ended up breaking up Wasm's Chromium CI (https://chromium-review.googlesource.com/c/emscripten-releases/+/5500231) because the way the table index is encoded is different from MVP (u32) vs. reference-types (LEB), which caused different encodings for call_indirect.

And Chromium CI's and Emscripten's minimum required node version is v16, which does not yet support reference-types, which does not recognize that table index encoding. reference-types is first supported in node v17.2.

We knew the current minimum required node for Emscripten (v16) did not support reference-types, but thought it was fine because unless you explicitly use __funcref or __externref things would be fine, and if you want to use them explicitly, you would have a newer node. But it turned out it also affected the encoding of call_indirect.

While we are discussing the potential solutions, I will disable reference-types to unblock the rolls.

[llvmbot]

@llvm/pr-subscribers-backend-webassembly

@llvm/pr-subscribers-clang

Author: Heejin Ahn (aheejin)

Changes

#80923 newly enabled multivalue and reference-types in the generic CPU.
But enabling reference-types ended up breaking up Wasm's Chromium CI (https://chromium-review.googlesource.com/c/emscripten-releases/+/5500231) because the way the table index is encoded different from MVP (u32) vs. reference-types (LEB), which caused different encodings for call_indirect.

And Chromium CI's and Emscripten's minimum required node version is v16, which does not yet support reference-types, which does not recognize that table index encoding. reference-types is first supported in node v17.2.

We knew the current minimum required node for Emscripten (v16) did not support reference-types, but thought it was fine because unless you explicitly use __funcref or __externref things would be fine, and if you want to use them explicitly, you would have a newer node. But it turned out it also affected the encoding of call_indirect.

While we are discussing the potential solutions, I will disable reference-types to unblock the rolls.

---

Full diff: https://github.com/llvm/llvm-project/pull/90792.diff

3 Files Affected:

• (modified) clang/docs/ReleaseNotes.rst (+4-4)
• (modified) clang/lib/Basic/Targets/WebAssembly.cpp (+1-1)
• (modified) clang/test/Preprocessor/wasm-target-features.c (+1-1)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 2c5308fbcb319a..0e3f7cf89ca885 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -742,10 +742,10 @@ AIX Support
 WebAssembly Support
 ^^^^^^^^^^^^^^^^^^^
 
-The -mcpu=generic configuration now enables multivalue and reference-types.These
-proposals are standardized and available in all major engines. Enabling
-multivalue here only enables the language feature but does not turn on the
-multivalue ABI (this enables non-ABI uses of multivalue, like exnref).
+The -mcpu=generic configuration now enables multivalue feature, which is
+standardized and available in all major engines. Enabling multivalue here only
+enables the language feature but does not turn on the multivalue ABI (this
+enables non-ABI uses of multivalue, like exnref).
 
 AVR Support
 ^^^^^^^^^^^
diff --git a/clang/lib/Basic/Targets/WebAssembly.cpp b/clang/lib/Basic/Targets/WebAssembly.cpp
index 1f0418b21c1f86..a6d820e108088f 100644
--- a/clang/lib/Basic/Targets/WebAssembly.cpp
+++ b/clang/lib/Basic/Targets/WebAssembly.cpp
@@ -153,7 +153,6 @@ bool WebAssemblyTargetInfo::initFeatureMap(
   auto addGenericFeatures = [&]() {
     Features["multivalue"] = true;
     Features["mutable-globals"] = true;
-    Features["reference-types"] = true;
     Features["sign-ext"] = true;
   };
   auto addBleedingEdgeFeatures = [&]() {
@@ -162,6 +161,7 @@ bool WebAssemblyTargetInfo::initFeatureMap(
     Features["bulk-memory"] = true;
     Features["multimemory"] = true;
     Features["nontrapping-fptoint"] = true;
+    Features["reference-types"] = true;
     Features["tail-call"] = true;
     Features["half-precision"] = true;
     setSIMDLevel(Features, SIMD128, true);
diff --git a/clang/test/Preprocessor/wasm-target-features.c b/clang/test/Preprocessor/wasm-target-features.c
index 72ecc60a6e7898..5a4f85461d5aa2 100644
--- a/clang/test/Preprocessor/wasm-target-features.c
+++ b/clang/test/Preprocessor/wasm-target-features.c
@@ -164,7 +164,6 @@
 //
 // GENERIC-INCLUDE-DAG: #define __wasm_multivalue__ 1{{$}}
 // GENERIC-INCLUDE-DAG: #define __wasm_mutable_globals__ 1{{$}}
-// GENERIC-INCLUDE-DAG: #define __wasm_reference_types__ 1{{$}}
 // GENERIC-INCLUDE-DAG: #define __wasm_sign_ext__ 1{{$}}
 //
 // RUN: %clang -E -dM %s -o - 2>&1 \
@@ -181,6 +180,7 @@
 // GENERIC-NOT: #define __wasm_half_precision__ 1{{$}}
 // GENERIC-NOT: #define __wasm_multimemory__ 1{{$}}
 // GENERIC-NOT: #define __wasm_nontrapping_fptoint__ 1{{$}}
+// GENERIC-NOT: #define __wasm_reference_types__ 1{{$}}
 // GENERIC-NOT: #define __wasm_relaxed_simd__ 1{{$}}
 // GENERIC-NOT: #define __wasm_simd128__ 1{{$}}
 // GENERIC-NOT: #define __wasm_tail_call__ 1{{$}}

[aheejin]

Will land this given that this is necessary to unblock the rolls and the full CI will take more than a full day.