[CIR] Remove ABI handling from CIRGen call handling (llvm#1604)

Remove all the code the manages ABI info for arguments and return values
in the initial CIR codegen. We prefer for the CIR to represent the types
as they appear in the source code, with ABI handling being deferred
until the lowering phase or calling convention transform.

The ABI handling being removed here was brought over from the classic
codegen, but none of the effects being computed made it into the CIR so
this change is effectively NFC.

This change leaves the `CIRGenFunctionInfoArgInfo` with just one member.
That can be cleaned up in a later patch.

Author: andykaylor

clang/lib/CIR/CodeGen/ABIInfo.h

@@ -34,8 +34,6 @@ class ABIInfo {
   CIRGenCXXABI &getCXXABI() const;
   clang::ASTContext &getContext() const;
 
-  virtual void computeInfo(CIRGenFunctionInfo &FI) const = 0;
-
   virtual bool allowBFloatArgsAndRet() const { return false; }
 
   // Implement the Type::IsPromotableIntegerType for ABI specific needs. The

clang/lib/CIR/CodeGen/CIRAsm.cpp

@@ -521,20 +521,6 @@ mlir::LogicalResult CIRGenFunction::emitAsmStmt(const AsmStmt &S) {
     }
   } // iterate over output operands
 
-  // If this is a Microsoft-style asm blob, store the return registers (EAX:EDX)
-  // to the return value slot. Only do this when returning in registers.
-  if (isa<MSAsmStmt>(&S)) {
-    const cir::ABIArgInfo &RetAI = CurFnInfo->getReturnInfo();
-    if (RetAI.isDirect() || RetAI.isExtend()) {
-      // Make a fake lvalue for the return value slot.
-      LValue ReturnSlot = makeAddrLValue(ReturnValue, FnRetTy);
-      CGM.getTargetCIRGenInfo().addReturnRegisterOutputs(
-          *this, ReturnSlot, Constraints, ResultRegTypes, ResultTruncRegTypes,
-          ResultRegDests, AsmString, S.getNumOutputs());
-      SawAsmBlock = true;
-    }
-  }
-
   for (unsigned i = 0, e = S.getNumInputs(); i != e; i++) {
     const Expr *InputExpr = S.getInputExpr(i);