GlobalISel: Fix generic handling of single outgoing call arguments

Simply call the argument handler like is done for the incoming
case. This will allow removal of hacks in the AMDGPU call lowering in
a future change.

llvm/lib/CodeGen/GlobalISel/CallLowering.cpp

@@ -241,12 +241,20 @@ bool CallLowering::handleAssignments(CCState &CCInfo,
     // we currently support.
     unsigned NumParts = TLI->getNumRegistersForCallingConv(
         F.getContext(), F.getCallingConv(), CurVT);
-    if (NumParts > 1) {
-      // For now only handle exact splits.
-      if (NewVT.getSizeInBits() * NumParts != CurVT.getSizeInBits())
+
+    if (NumParts == 1) {
+      // Try to use the register type if we couldn't assign the VT.
+      if (Handler.assignArg(i, NewVT, NewVT, CCValAssign::Full, Args[i],
+                            Args[i].Flags[0], CCInfo))
         return false;
+      continue;
     }
 
+    assert(NumParts > 1);
+    // For now only handle exact splits.
+    if (NewVT.getSizeInBits() * NumParts != CurVT.getSizeInBits())
+      return false;
+
     // For incoming arguments (physregs to vregs), we could have values in
     // physregs (or memlocs) which we want to extract and copy to vregs.
     // During this, we might have to deal with the LLT being split across
@@ -256,47 +264,36 @@ bool CallLowering::handleAssignments(CCState &CCInfo,
     // vreg with an LLT which we want to assign to a physical location, and
     // we might have to record that the value has to be split later.
     if (Handler.isIncomingArgumentHandler()) {
-      if (NumParts == 1) {
-        // Try to use the register type if we couldn't assign the VT.
+      // We're handling an incoming arg which is split over multiple regs.
+      // E.g. passing an s128 on AArch64.
+      ISD::ArgFlagsTy OrigFlags = Args[i].Flags[0];
+      Args[i].OrigRegs.push_back(Args[i].Regs[0]);
+      Args[i].Regs.clear();
+      Args[i].Flags.clear();
+      LLT NewLLT = getLLTForMVT(NewVT);
+      // For each split register, create and assign a vreg that will store
+      // the incoming component of the larger value. These will later be
+      // merged to form the final vreg.
+      for (unsigned Part = 0; Part < NumParts; ++Part) {
+        Register Reg =
+            MIRBuilder.getMRI()->createGenericVirtualRegister(NewLLT);
+        ISD::ArgFlagsTy Flags = OrigFlags;
+        if (Part == 0) {
+          Flags.setSplit();
+        } else {
+          Flags.setOrigAlign(Align(1));
+          if (Part == NumParts - 1)
+            Flags.setSplitEnd();
+        }
+        Args[i].Regs.push_back(Reg);
+        Args[i].Flags.push_back(Flags);
         if (Handler.assignArg(i, NewVT, NewVT, CCValAssign::Full, Args[i],
-                              Args[i].Flags[0], CCInfo))
+                              Args[i].Flags[Part], CCInfo)) {
+          // Still couldn't assign this smaller part type for some reason.
           return false;
-      } else {
-        // We're handling an incoming arg which is split over multiple regs.
-        // E.g. passing an s128 on AArch64.
-        ISD::ArgFlagsTy OrigFlags = Args[i].Flags[0];
-        Args[i].OrigRegs.push_back(Args[i].Regs[0]);
-        Args[i].Regs.clear();
-        Args[i].Flags.clear();
-        LLT NewLLT = getLLTForMVT(NewVT);
-        // For each split register, create and assign a vreg that will store
-        // the incoming component of the larger value. These will later be
-        // merged to form the final vreg.
-        for (unsigned Part = 0; Part < NumParts; ++Part) {
-          Register Reg =
-              MIRBuilder.getMRI()->createGenericVirtualRegister(NewLLT);
-          ISD::ArgFlagsTy Flags = OrigFlags;
-          if (Part == 0) {
-            Flags.setSplit();
-          } else {
-            Flags.setOrigAlign(Align(1));
-            if (Part == NumParts - 1)
-              Flags.setSplitEnd();
-          }
-          Args[i].Regs.push_back(Reg);
-          Args[i].Flags.push_back(Flags);
-          if (Handler.assignArg(i, NewVT, NewVT, CCValAssign::Full,
-                                Args[i], Args[i].Flags[Part], CCInfo)) {
-            // Still couldn't assign this smaller part type for some reason.
-            return false;
-          }
         }
       }
     } else {
-      // Handling an outgoing arg that might need to be split.
-      if (NumParts < 2)
-        return false; // Don't know how to deal with this type combination.
-
       // This type is passed via multiple registers in the calling convention.
       // We need to extract the individual parts.
       Register LargeReg = Args[i].Regs[0];