[WebAssembly] Disable multivalue emission temporarily (llvm#82714)

We plan to enable multivalue in the features section soon (llvm#80923) for
other reasons, such as the feature having been standardized for many
years and other features being developed (e.g. EH) depending on it. This
is separate from enabling Clang experimental multivalue ABI (`-Xclang
-target-abi -Xclang experimental-mv`), but it turned out we generate
some multivalue code in the backend as well if it is enabled in the
features section.

Given that our backend multivalue generation still has not been much
used nor tested, and enabling the feature in the features section can be
a separate decision from how much multialue (including none) we decide
to generate for now, I'd like to temporarily disable the actual
generation of multivalue in our backend. To do that, this adds an
internal flag `-wasm-emit-multivalue` that defaults to false. All our
existing multivalue tests can use this to test multivalue code. This
flag can be removed later when we are confident the multivalue
generation is well tested.

llvm/lib/Target/WebAssembly/WebAssemblyISelLowering.cpp

@@ -43,6 +43,8 @@ using namespace llvm;
 
 #define DEBUG_TYPE "wasm-lower"
 
+extern cl::opt<bool> WasmEmitMultiValue;
+
 WebAssemblyTargetLowering::WebAssemblyTargetLowering(
     const TargetMachine &TM, const WebAssemblySubtarget &STI)
     : TargetLowering(TM), Subtarget(&STI) {
@@ -1288,15 +1290,16 @@ bool WebAssemblyTargetLowering::CanLowerReturn(
     const SmallVectorImpl<ISD::OutputArg> &Outs,
     LLVMContext & /*Context*/) const {
   // WebAssembly can only handle returning tuples with multivalue enabled
-  return Subtarget->hasMultivalue() || Outs.size() <= 1;
+  return (Subtarget->hasMultivalue() && WasmEmitMultiValue) || Outs.size() <= 1;
 }
 
 SDValue WebAssemblyTargetLowering::LowerReturn(
     SDValue Chain, CallingConv::ID CallConv, bool /*IsVarArg*/,
     const SmallVectorImpl<ISD::OutputArg> &Outs,
     const SmallVectorImpl<SDValue> &OutVals, const SDLoc &DL,
     SelectionDAG &DAG) const {
-  assert((Subtarget->hasMultivalue() || Outs.size() <= 1) &&
+  assert(((Subtarget->hasMultivalue() && WasmEmitMultiValue) ||
+          Outs.size() <= 1) &&
          "MVP WebAssembly can only return up to one value");
   if (!callingConvSupported(CallConv))
     fail(DL, DAG, "WebAssembly doesn't support non-C calling conventions");

llvm/lib/Target/WebAssembly/WebAssemblyMachineFunctionInfo.cpp

@@ -22,6 +22,8 @@
 #include "llvm/Target/TargetMachine.h"
 using namespace llvm;
 
+extern cl::opt<bool> WasmEmitMultiValue;
+
 WebAssemblyFunctionInfo::~WebAssemblyFunctionInfo() = default; // anchor.
 
 MachineFunctionInfo *WebAssemblyFunctionInfo::clone(
@@ -71,7 +73,8 @@ void llvm::computeSignatureVTs(const FunctionType *Ty,
 
   MVT PtrVT = MVT::getIntegerVT(TM.createDataLayout().getPointerSizeInBits());
   if (Results.size() > 1 &&
-      !TM.getSubtarget<WebAssemblySubtarget>(ContextFunc).hasMultivalue()) {
+      (!TM.getSubtarget<WebAssemblySubtarget>(ContextFunc).hasMultivalue() ||
+       !WasmEmitMultiValue)) {
     // WebAssembly can't lower returns of multiple values without demoting to
     // sret unless multivalue is enabled (see
     // WebAssemblyTargetLowering::CanLowerReturn). So replace multiple return

llvm/lib/Target/WebAssembly/WebAssemblyRuntimeLibcallSignatures.cpp

@@ -24,6 +24,8 @@
 
 using namespace llvm;
 
+extern cl::opt<bool> WasmEmitMultiValue;
+
 namespace {
 
 enum RuntimeLibcallSignature {
@@ -694,7 +696,7 @@ void llvm::getLibcallSignature(const WebAssemblySubtarget &Subtarget,
     Params.push_back(PtrTy);
     break;
   case i64_i64_func_f32:
-    if (Subtarget.hasMultivalue()) {
+    if (Subtarget.hasMultivalue() && WasmEmitMultiValue) {
       Rets.push_back(wasm::ValType::I64);
       Rets.push_back(wasm::ValType::I64);
     } else {
@@ -703,7 +705,7 @@ void llvm::getLibcallSignature(const WebAssemblySubtarget &Subtarget,
     Params.push_back(wasm::ValType::F32);
     break;
   case i64_i64_func_f64:
-    if (Subtarget.hasMultivalue()) {
+    if (Subtarget.hasMultivalue() && WasmEmitMultiValue) {
       Rets.push_back(wasm::ValType::I64);
       Rets.push_back(wasm::ValType::I64);
     } else {
@@ -712,7 +714,7 @@ void llvm::getLibcallSignature(const WebAssemblySubtarget &Subtarget,
     Params.push_back(wasm::ValType::F64);
     break;
   case i16_i16_func_i16_i16:
-    if (Subtarget.hasMultivalue()) {
+    if (Subtarget.hasMultivalue() && WasmEmitMultiValue) {
       Rets.push_back(wasm::ValType::I32);
       Rets.push_back(wasm::ValType::I32);
     } else {
@@ -722,7 +724,7 @@ void llvm::getLibcallSignature(const WebAssemblySubtarget &Subtarget,
     Params.push_back(wasm::ValType::I32);
     break;
   case i32_i32_func_i32_i32:
-    if (Subtarget.hasMultivalue()) {
+    if (Subtarget.hasMultivalue() && WasmEmitMultiValue) {
       Rets.push_back(wasm::ValType::I32);
       Rets.push_back(wasm::ValType::I32);
     } else {
@@ -732,7 +734,7 @@ void llvm::getLibcallSignature(const WebAssemblySubtarget &Subtarget,
     Params.push_back(wasm::ValType::I32);
     break;
   case i64_i64_func_i64_i64:
-    if (Subtarget.hasMultivalue()) {
+    if (Subtarget.hasMultivalue() && WasmEmitMultiValue) {
       Rets.push_back(wasm::ValType::I64);
       Rets.push_back(wasm::ValType::I64);
     } else {
@@ -742,7 +744,7 @@ void llvm::getLibcallSignature(const WebAssemblySubtarget &Subtarget,
     Params.push_back(wasm::ValType::I64);
     break;
   case i64_i64_func_i64_i64_i64_i64:
-    if (Subtarget.hasMultivalue()) {
+    if (Subtarget.hasMultivalue() && WasmEmitMultiValue) {
       Rets.push_back(wasm::ValType::I64);
       Rets.push_back(wasm::ValType::I64);
     } else {
@@ -754,7 +756,7 @@ void llvm::getLibcallSignature(const WebAssemblySubtarget &Subtarget,
     Params.push_back(wasm::ValType::I64);
     break;
   case i64_i64_func_i64_i64_i64_i64_iPTR:
-    if (Subtarget.hasMultivalue()) {
+    if (Subtarget.hasMultivalue() && WasmEmitMultiValue) {
       Rets.push_back(wasm::ValType::I64);
       Rets.push_back(wasm::ValType::I64);
     } else {
@@ -767,7 +769,7 @@ void llvm::getLibcallSignature(const WebAssemblySubtarget &Subtarget,
     Params.push_back(PtrTy);
     break;
   case i64_i64_i64_i64_func_i64_i64_i64_i64:
-    if (Subtarget.hasMultivalue()) {
+    if (Subtarget.hasMultivalue() && WasmEmitMultiValue) {
       Rets.push_back(wasm::ValType::I64);
       Rets.push_back(wasm::ValType::I64);
       Rets.push_back(wasm::ValType::I64);
@@ -781,7 +783,7 @@ void llvm::getLibcallSignature(const WebAssemblySubtarget &Subtarget,
     Params.push_back(wasm::ValType::I64);
     break;
   case i64_i64_func_i64_i64_i32:
-    if (Subtarget.hasMultivalue()) {
+    if (Subtarget.hasMultivalue() && WasmEmitMultiValue) {
       Rets.push_back(wasm::ValType::I64);
       Rets.push_back(wasm::ValType::I64);
     } else {
@@ -851,7 +853,7 @@ void llvm::getLibcallSignature(const WebAssemblySubtarget &Subtarget,
     Params.push_back(wasm::ValType::I64);
     break;
   case i64_i64_func_i64_i64_i64_i64_i64_i64:
-    if (Subtarget.hasMultivalue()) {
+    if (Subtarget.hasMultivalue() && WasmEmitMultiValue) {
       Rets.push_back(wasm::ValType::I64);
       Rets.push_back(wasm::ValType::I64);
     } else {
@@ -865,7 +867,7 @@ void llvm::getLibcallSignature(const WebAssemblySubtarget &Subtarget,
     Params.push_back(wasm::ValType::I64);
     break;
   case i64_i64_func_i32:
-    if (Subtarget.hasMultivalue()) {
+    if (Subtarget.hasMultivalue() && WasmEmitMultiValue) {
       Rets.push_back(wasm::ValType::I64);
       Rets.push_back(wasm::ValType::I64);
     } else {
@@ -874,7 +876,7 @@ void llvm::getLibcallSignature(const WebAssemblySubtarget &Subtarget,
     Params.push_back(wasm::ValType::I32);
     break;
   case i64_i64_func_i64:
-    if (Subtarget.hasMultivalue()) {
+    if (Subtarget.hasMultivalue() && WasmEmitMultiValue) {
       Rets.push_back(wasm::ValType::I64);
       Rets.push_back(wasm::ValType::I64);
     } else {

llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp

@@ -54,6 +54,15 @@ static cl::opt<bool> WasmDisableFixIrreducibleControlFlowPass(
              " irreducible control flow optimization pass"),
     cl::init(false));
 
+// A temporary option to control emission of multivalue until multivalue
+// implementation is stable enough. We currently don't emit multivalue by
+// default even if the feature section allows it.
+// TODO Stabilize multivalue and delete this option
+cl::opt<bool>
+    WasmEmitMultiValue("wasm-emit-multivalue", cl::Hidden,
+                       cl::desc("WebAssembly: Emit multivalue in the backend"),
+                       cl::init(false));
+
 extern "C" LLVM_EXTERNAL_VISIBILITY void LLVMInitializeWebAssemblyTarget() {
   // Register the target.
   RegisterTargetMachine<WebAssemblyTargetMachine> X(

llvm/test/CodeGen/WebAssembly/lower-em-ehsjlj-multi-return.ll

@@ -1,5 +1,5 @@
-; RUN: not --crash llc < %s -enable-emscripten-cxx-exceptions -mattr=+multivalue 2>&1 | FileCheck %s --check-prefix=EH
-; RUN: not --crash llc < %s -enable-emscripten-sjlj -mattr=+multivalue 2>&1 | FileCheck %s --check-prefix=SJLJ
+; RUN: not --crash llc < %s -enable-emscripten-cxx-exceptions -mattr=+multivalue -wasm-emit-multivalue 2>&1 | FileCheck %s --check-prefix=EH
+; RUN: not --crash llc < %s -enable-emscripten-sjlj -mattr=+multivalue 2>&1 -wasm-emit-multivalue | FileCheck %s --check-prefix=SJLJ
 
 ; Currently multivalue returning functions are not supported in Emscripten EH /
 ; SjLj. Make sure they error out.

llvm/test/CodeGen/WebAssembly/multivalue-dont-move-def-past-use.mir

@@ -1,5 +1,5 @@
 # NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
-# RUN: llc -mtriple=wasm32-unknown-unknown -mattr=+multivalue -run-pass=wasm-reg-stackify -verify-machineinstrs %s -o - | FileCheck %s
+# RUN: llc -mtriple=wasm32-unknown-unknown -mattr=+multivalue -wasm-emit-multivalue -run-pass=wasm-reg-stackify -verify-machineinstrs %s -o - | FileCheck %s
 
 --- |
   target datalayout = "e-m:e-p:32:32-p10:8:8-p20:8:8-i64:64-n32:64-S128-ni:1:10:20"

llvm/test/CodeGen/WebAssembly/multivalue-stackify.ll

@@ -1,7 +1,7 @@
 ; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
 ; NOTE: Test functions have been generated by multivalue-stackify.py.
 
-; RUN: llc < %s -verify-machineinstrs -mattr=+multivalue | FileCheck %s
+; RUN: llc < %s -verify-machineinstrs -mattr=+multivalue -wasm-emit-multivalue | FileCheck %s
 
 ; Test that the multivalue stackification works
 

llvm/test/CodeGen/WebAssembly/multivalue.ll

@@ -1,7 +1,8 @@
-; RUN: llc < %s -asm-verbose=false -verify-machineinstrs -mcpu=mvp -mattr=+multivalue,+tail-call | FileCheck %s
-; RUN: llc < %s -asm-verbose=false -verify-machineinstrs -mcpu=mvp -mattr=+reference-types,+multivalue,+tail-call | FileCheck --check-prefix REF %s
-; RUN: llc < %s -asm-verbose=false -verify-machineinstrs -disable-wasm-fallthrough-return-opt -wasm-disable-explicit-locals -wasm-keep-registers -mcpu=mvp -mattr=+multivalue,+tail-call | FileCheck %s --check-prefix REGS
-; RUN: llc < %s --filetype=obj -mcpu=mvp -mattr=+multivalue,+tail-call | obj2yaml | FileCheck %s --check-prefix OBJ
+; RUN: llc < %s -asm-verbose=false -verify-machineinstrs -mcpu=mvp -mattr=+multivalue,+tail-call -wasm-emit-multivalue | FileCheck %s
+; RUN: llc < %s -asm-verbose=false -verify-machineinstrs -mcpu=mvp -mattr=+reference-types,+multivalue,+tail-call -wasm-emit-multivalue | FileCheck --check-prefix REF %s
+; RUN: llc < %s -asm-verbose=false -verify-machineinstrs -disable-wasm-fallthrough-return-opt -wasm-disable-explicit-locals -wasm-keep-registers -mcpu=mvp -mattr=+multivalue,+tail-call -wasm-emit-multivalue | FileCheck %s --check-prefix REGS
+; RUN: llc < %s --filetype=obj -mcpu=mvp -mattr=+multivalue,+tail-call -wasm-emit-multivalue | obj2yaml | FileCheck %s --check-prefix OBJ
+; RUN: llc < %s -asm-verbose=false -verify-machineinstrs -mcpu=mvp -mattr=+multivalue,+tail-call | FileCheck %s --check-prefix NO-MULTIVALUE
 
 ; Test that the multivalue calls, returns, function types, and block
 ; types work as expected.
@@ -19,6 +20,7 @@ declare void @use_i64(i64)
 ; CHECK-NEXT: i32.const 42{{$}}
 ; CHECK-NEXT: i64.const 42{{$}}
 ; CHECK-NEXT: end_function{{$}}
+; NO-MULTIVALUE-NOT: .functype pair_const () -> (i32, i64)
 define %pair @pair_const() {
   ret %pair { i32 42, i64 42 }
 }

llvm/test/CodeGen/WebAssembly/multivalue_libcall.ll

@@ -1,5 +1,5 @@
 ; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 2
-; RUN: llc < %s -verify-machineinstrs -mcpu=mvp -mattr=+multivalue | FileCheck %s --check-prefix=MULTIVALUE
+; RUN: llc < %s -verify-machineinstrs -mcpu=mvp -mattr=+multivalue -wasm-emit-multivalue | FileCheck %s --check-prefix=MULTIVALUE
 ; RUN: llc < %s -verify-machineinstrs -mcpu=mvp | FileCheck %s --check-prefix=NO_MULTIVALUE
 
 ; Test libcall signatures when multivalue is enabled and disabled