[IRGen][wasm] Disable manual indirection for coroutine yielding results

`clang::CodeGen::swiftcall::shouldPassIndirectly` now returns true for
multiple scalar values on wasm targets because the Wasm MVP does not
support multiple return values. For such targets where we can't
directly return two pointers, we should not attempt to indirect at this
stage because the later MC lowering will also indirect the return.

Author: kateinoigakukun

lib/IRGen/GenCall.cpp

@@ -856,7 +856,6 @@ void SignatureExpansion::expandCoroutineResult(bool forContinuation) {
   auto fnConv = getSILFuncConventions();
   for (auto yield : FnType->getYields()) {
     YieldSchema schema(IGM, fnConv, yield);
-
     // If the individual value must be yielded indirectly, add a pointer.
     if (schema.isIndirect()) {
       components.push_back(schema.getIndirectPointerType(IGM));
@@ -870,26 +869,30 @@ void SignatureExpansion::expandCoroutineResult(bool forContinuation) {
   }
 
   // Find the maximal sequence of the component types that we can
-  // convince the ABI to pass directly.
+  // convince the ABI to pass directly if the target supports
+  // directly returning at least two pointers.
   // When counting components, ignore the continuation pointer.
-  unsigned numDirectComponents = components.size() - 1;
   SmallVector<llvm::Type*, 8> overflowTypes;
-  while (clang::CodeGen::swiftcall::
-                shouldPassIndirectly(IGM.ClangCodeGen->CGM(), components,
-                                     /*asReturnValue*/ true)) {
-    // If we added a pointer to the end of components, remove it.
-    if (!overflowTypes.empty()) components.pop_back();
+  unsigned numDirectComponents = components.size() - 1;
+  if (IGM.TargetInfo.SupportsDirectReturningAtLeastTwoPointers) {
+    while (clang::CodeGen::swiftcall::shouldPassIndirectly(
+        IGM.ClangCodeGen->CGM(), components,
+        /*asReturnValue*/ true)) {
+      // If we added a pointer to the end of components, remove it.
+      if (!overflowTypes.empty())
+        components.pop_back();
 
-    // Remove the last component and add it as an overflow type.
-    overflowTypes.push_back(components.pop_back_val());
-    --numDirectComponents;
+      // Remove the last component and add it as an overflow type.
+      overflowTypes.push_back(components.pop_back_val());
+      --numDirectComponents;
 
-    // Add a pointer to the end of components.
-    components.push_back(IGM.Int8PtrTy);
-  }
+      // Add a pointer to the end of components.
+      components.push_back(IGM.Int8PtrTy);
+    }
 
-  // We'd better have been able to pass at least two pointers.
-  assert(components.size() >= 2 || overflowTypes.empty());
+    // We'd better have been able to pass at least two pointers.
+    assert(components.size() >= 2 || overflowTypes.empty());
+  }
   CoroInfo.NumDirectYieldComponents = numDirectComponents;
 
   // Replace the pointer type we added to components with the real