[WebAssembly] Make returns variadic

Summary:
This is necessary and sufficient to get simple cases of multiple
return working with multivalue enabled. More complex cases will
require block and loop signatures to be generalized to potentially be
type indices as well.

Reviewers: aheejin, dschuff

Subscribers: sbc100, jgravelle-google, hiraditya, sunfish, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D68684

llvm-svn: 374235

1 files changed, 4 insertions, 3 deletions

diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyISelLowering.cpp b/llvm/lib/Target/WebAssembly/WebAssemblyISelLowering.cpp
index 538234384af..aff379585f2 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyISelLowering.cpp
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyISelLowering.cpp
@@ -852,8 +852,8 @@ bool WebAssemblyTargetLowering::CanLowerReturn(
     CallingConv::ID /*CallConv*/, MachineFunction & /*MF*/, bool /*IsVarArg*/,
     const SmallVectorImpl<ISD::OutputArg> &Outs,
     LLVMContext & /*Context*/) const {
-  // WebAssembly can't currently handle returning tuples.
-  return Outs.size() <= 1;
+  // WebAssembly can only handle returning tuples with multivalue enabled
+  return Subtarget->hasMultivalue() || Outs.size() <= 1;
 }
 
 SDValue WebAssemblyTargetLowering::LowerReturn(
@@ -861,7 +861,8 @@ SDValue WebAssemblyTargetLowering::LowerReturn(
     const SmallVectorImpl<ISD::OutputArg> &Outs,
     const SmallVectorImpl<SDValue> &OutVals, const SDLoc &DL,
     SelectionDAG &DAG) const {
-  assert(Outs.size() <= 1 && "WebAssembly can only return up to one value");
+  assert(Subtarget->hasMultivalue() ||
+         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");