[WebAssembly] Support swiftself and swifterror for WebAssembly target

Summary:
Swift ABI is based on basic C ABI described here https://github.com/WebAssembly/tool-conventions/blob/master/BasicCABI.md
Swift Calling Convention on WebAssembly is a little deffer from swiftcc
on another architectures.

On non WebAssembly arch, swiftcc accepts extra parameters that are
attributed with swifterror or swiftself by caller. Even if callee
doesn't have these parameters, the invocation succeed ignoring extra
parameters.

But WebAssembly strictly checks that callee and caller signatures are
same. https://github.com/WebAssembly/design/blob/master/Semantics.md#calls
So at WebAssembly level, all swiftcc functions end up extra arguments
and all function definitions and invocations explicitly have additional
parameters to fill swifterror and swiftself.

This patch support signature difference for swiftself and swifterror cc
is swiftcc.

e.g.
```
declare swiftcc void @foo(i32, i32)
@data = global i8* bitcast (void (i32, i32)* @foo to i8*)
define swiftcc void @bar() {
  %1 = load i8*, i8** @data
  %2 = bitcast i8* %1 to void (i32, i32, i32)*
  call swiftcc void %2(i32 1, i32 2, i32 swiftself 3)
  ret void
}
```

For swiftcc, emit additional swiftself and swifterror parameters
if there aren't while lowering. These additional parameters are added
for both callee and caller.
They are necessary to match callee and caller signature for direct and
indirect function call.

Differential Revision: https://reviews.llvm.org/D76049

1 files changed, 6 insertions, 0 deletions

diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyFastISel.cpp b/llvm/lib/Target/WebAssembly/WebAssemblyFastISel.cpp
index 10d90d1..f7e9880 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyFastISel.cpp
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyFastISel.cpp
@@ -640,6 +640,9 @@ bool WebAssemblyFastISel::fastLowerArguments() {
   if (F->isVarArg())
     return false;
 
+  if (FuncInfo.Fn->getCallingConv() == CallingConv::Swift)
+    return false;
+
   unsigned I = 0;
   for (auto const &Arg : F->args()) {
     const AttributeList &Attrs = F->getAttributes();
@@ -754,6 +757,9 @@ bool WebAssemblyFastISel::selectCall(const Instruction *I) {
   if (Func && Func->isIntrinsic())
     return false;
 
+  if (Call->getCallingConv() == CallingConv::Swift)
+    return false;
+
   bool IsDirect = Func != nullptr;
   if (!IsDirect && isa<ConstantExpr>(Call->getCalledValue()))
     return false;