[GlobalISel] Add the necessary plumbing to lower formal arguments.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@260579 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Target/TargetLowering.h

@@ -33,6 +33,9 @@
 #include "llvm/IR/Attributes.h"
 #include "llvm/IR/CallSite.h"
 #include "llvm/IR/CallingConv.h"
+#ifdef LLVM_BUILD_GLOBAL_ISEL
+#  include "llvm/IR/Function.h"
+#endif
 #include "llvm/IR/IRBuilder.h"
 #include "llvm/IR/InlineAsm.h"
 #include "llvm/IR/Instructions.h"
@@ -2517,6 +2520,22 @@ class TargetLowering : public TargetLoweringBase {
                            unsigned VReg) const {
     return false;
   }
+
+  /// This hook must be implemented to lower the incoming (formal)
+  /// arguments, described by \p Args, for GlobalISel. Each argument
+  /// must end up in the related virtual register described by VRegs.
+  /// In other words, the first argument should end up in VRegs[0],
+  /// the second in VRegs[1], and so on.
+  /// \p MIRBuilder is set to the proper insertion for the argument
+  /// lowering.
+  ///
+  /// \return True if the lowering succeeded, false otherwise.
+  virtual bool
+  LowerFormalArguments(MachineIRBuilder &MIRBuilder,
+                       const Function::ArgumentListType &Args,
+                       const SmallVectorImpl<unsigned> &VRegs) const {
+    return false;
+  }
 #endif
 
   /// Return true if result of the specified node is used by a return node

lib/CodeGen/GlobalISel/IRTranslator.cpp

@@ -12,6 +12,7 @@
 
 #include "llvm/CodeGen/GlobalISel/IRTranslator.h"
 
+#include "llvm/ADT/SmallVector.h"
 #include "llvm/CodeGen/MachineFunction.h"
 #include "llvm/CodeGen/MachineRegisterInfo.h"
 #include "llvm/IR/Constant.h"
@@ -103,9 +104,22 @@ void IRTranslator::finalize() {
 
 bool IRTranslator::runOnMachineFunction(MachineFunction &MF) {
   const Function &F = *MF.getFunction();
+  if (F.empty())
+    return false;
   TLI = MF.getSubtarget().getTargetLowering();
   MIRBuilder.setFunction(MF);
   MRI = &MF.getRegInfo();
+  // Setup the arguments.
+  MachineBasicBlock &MBB = getOrCreateBB(&F.front());
+  MIRBuilder.setBasicBlock(MBB);
+  SmallVector<unsigned, 8> VRegArgs;
+  for (const Argument &Arg: F.args())
+    VRegArgs.push_back(*getOrCreateVRegs(&Arg).begin());
+  bool Succeeded = TLI->LowerFormalArguments(MIRBuilder, F.getArgumentList(),
+                                             VRegArgs);
+  if (!Succeeded)
+    report_fatal_error("Unable to lower arguments");
+
   for (const BasicBlock &BB: F) {
     MachineBasicBlock &MBB = getOrCreateBB(&BB);
     MIRBuilder.setBasicBlock(MBB);