[AArch64][GlobalISel] Support returned argument with multiple registers

The call lowering code assumed that a returned argument could only
consist of one register. Pass an ArrayRef<Register> instead of
Register to make sure that all parts get assigned.

Fixes llvm/llvm-project#53315.

Differential Revision: https://reviews.llvm.org/D117866

llvm/include/llvm/CodeGen/GlobalISel/CallLowering.h

@@ -388,12 +388,12 @@ class CallLowering {
   /// \p Handler to move them to the assigned locations.
   ///
   /// \return True if everything has succeeded, false otherwise.
-  bool determineAndHandleAssignments(ValueHandler &Handler,
-                                     ValueAssigner &Assigner,
-                                     SmallVectorImpl<ArgInfo> &Args,
-                                     MachineIRBuilder &MIRBuilder,
-                                     CallingConv::ID CallConv, bool IsVarArg,
-                                     Register ThisReturnReg = Register()) const;
+  bool
+  determineAndHandleAssignments(ValueHandler &Handler, ValueAssigner &Assigner,
+                                SmallVectorImpl<ArgInfo> &Args,
+                                MachineIRBuilder &MIRBuilder,
+                                CallingConv::ID CallConv, bool IsVarArg,
+                                ArrayRef<Register> ThisReturnRegs = None) const;
 
   /// Use \p Handler to insert code to handle the argument/return values
   /// represented by \p Args. It's expected determineAssignments previously
@@ -402,7 +402,7 @@ class CallLowering {
                          CCState &CCState,
                          SmallVectorImpl<CCValAssign> &ArgLocs,
                          MachineIRBuilder &MIRBuilder,
-                         Register ThisReturnReg = Register()) const;
+                         ArrayRef<Register> ThisReturnRegs = None) const;
 
   /// Check whether parameters to a call that are passed in callee saved
   /// registers are the same as from the calling function.  This needs to be

llvm/lib/CodeGen/GlobalISel/CallLowering.cpp

@@ -509,7 +509,8 @@ static void buildCopyToRegs(MachineIRBuilder &B, ArrayRef<Register> DstRegs,
 bool CallLowering::determineAndHandleAssignments(
     ValueHandler &Handler, ValueAssigner &Assigner,
     SmallVectorImpl<ArgInfo> &Args, MachineIRBuilder &MIRBuilder,
-    CallingConv::ID CallConv, bool IsVarArg, Register ThisReturnReg) const {
+    CallingConv::ID CallConv, bool IsVarArg,
+    ArrayRef<Register> ThisReturnRegs) const {
   MachineFunction &MF = MIRBuilder.getMF();
   const Function &F = MF.getFunction();
   SmallVector<CCValAssign, 16> ArgLocs;
@@ -519,7 +520,7 @@ bool CallLowering::determineAndHandleAssignments(
     return false;
 
   return handleAssignments(Handler, Args, CCInfo, ArgLocs, MIRBuilder,
-                           ThisReturnReg);
+                           ThisReturnRegs);
 }
 
 static unsigned extendOpFromFlags(llvm::ISD::ArgFlagsTy Flags) {
@@ -596,7 +597,7 @@ bool CallLowering::handleAssignments(ValueHandler &Handler,
                                      CCState &CCInfo,
                                      SmallVectorImpl<CCValAssign> &ArgLocs,
                                      MachineIRBuilder &MIRBuilder,
-                                     Register ThisReturnReg) const {
+                                     ArrayRef<Register> ThisReturnRegs) const {
   MachineFunction &MF = MIRBuilder.getMF();
   MachineRegisterInfo &MRI = MF.getRegInfo();
   const Function &F = MF.getFunction();
@@ -740,10 +741,10 @@ bool CallLowering::handleAssignments(ValueHandler &Handler,
 
       assert(!VA.needsCustom() && "custom loc should have been handled already");
 
-      if (i == 0 && ThisReturnReg.isValid() &&
+      if (i == 0 && !ThisReturnRegs.empty() &&
           Handler.isIncomingArgumentHandler() &&
           isTypeIsValidForThisReturn(ValVT)) {
-        Handler.assignValueToReg(Args[i].Regs[i], ThisReturnReg, VA);
+        Handler.assignValueToReg(ArgReg, ThisReturnRegs[Part], VA);
         continue;
       }
 

llvm/lib/Target/AArch64/GISel/AArch64CallLowering.cpp

@@ -1179,7 +1179,7 @@ bool AArch64CallLowering::lowerCall(MachineIRBuilder &MIRBuilder,
     if (!determineAndHandleAssignments(
             UsingReturnedArg ? ReturnedArgHandler : Handler, Assigner, InArgs,
             MIRBuilder, Info.CallConv, Info.IsVarArg,
-            UsingReturnedArg ? OutArgs[0].Regs[0] : Register()))
+            UsingReturnedArg ? makeArrayRef(OutArgs[0].Regs) : None))
       return false;
   }
 

llvm/test/CodeGen/AArch64/pr53315-returned-i128.ll

@@ -0,0 +1,25 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc -O0 -mtriple=aarch64-unknown-linux-gnu -verify-machineinstrs < %s | FileCheck %s
+
+define void @test() nounwind {
+; CHECK-LABEL: test:
+; CHECK:       // %bb.0:
+; CHECK-NEXT:    sub sp, sp, #32
+; CHECK-NEXT:    str x30, [sp, #16] // 8-byte Folded Spill
+; CHECK-NEXT:    mov x1, xzr
+; CHECK-NEXT:    str x1, [sp, #8] // 8-byte Folded Spill
+; CHECK-NEXT:    mov x0, x1
+; CHECK-NEXT:    bl returns_arg
+; CHECK-NEXT:    ldr x1, [sp, #8] // 8-byte Folded Reload
+; CHECK-NEXT:    mov x0, x1
+; CHECK-NEXT:    bl accepts_arg
+; CHECK-NEXT:    ldr x30, [sp, #16] // 8-byte Folded Reload
+; CHECK-NEXT:    add sp, sp, #32
+; CHECK-NEXT:    ret
+  %x = call i128 @returns_arg(i128 0)
+  call void @accepts_arg(i128 %x)
+  ret void
+}
+
+declare i128 @returns_arg(i128 returned)
+declare void @accepts_arg(i128)