[AArch64][Windows] Check sret attribute also for inreg attribute

[bcl5980]

Summary

Fix the issue: #57684

[DavidSpickett]

I have zero idea what either InReg or SRet are, I'll leave the actual review to others.

llvm/test/CodeGen/AArch64/aarch64-windows-inreg-without-sret.ll

3 ↗

(On Diff #466274)

Please comment the intent of the test. E.g.

"When there is inreg but not sret, we should emit..."

[efriedma]

Code change looks fine

llvm/test/CodeGen/AArch64/aarch64-windows-inreg-without-sret.ll

7 ↗

(On Diff #466274)

Is there some other file we could put this in with other Windows calling convention stuff?

[bcl5980]

move the test to arm64-windows-calls.ll

[efriedma]

LGTM

llvm/lib/Target/AArch64/AArch64ISelLowering.cpp

if (isVarArg) {
     }
   }
 
   // On Windows, InReg pointers must be returned, so record the pointer in a
   // virtual register at the start of the function so it can be returned in the
   // epilogue.
   if (IsWin64) {
     for (unsigned I = 0, E = Ins.size(); I != E; ++I) {
-      if (Ins[I].Flags.isInReg()) {
+      if (Ins[I].Flags.isInReg() && Ins[I].Flags.isSRet()) {
         assert(!FuncInfo->getSRetReturnReg());
 
         MVT PtrTy = getPointerTy(DAG.getDataLayout());
         Register Reg =
             MF.getRegInfo().createVirtualRegister(getRegClassFor(PtrTy));
         FuncInfo->setSRetReturnReg(Reg);
 
         SDValue Copy = DAG.getCopyToReg(DAG.getEntryNode(), DL, Reg, InVals[I]);

llvm/test/CodeGen/AArch64/arm64-windows-calls.ll

 define void @call_copy_notpod() {
   %x = call [2 x i64] @copy_notpod(%struct.NotPod* @NotPod)
   %notpod = bitcast %struct.NotPod* @NotPod to [2 x i64]*
   store [2 x i64] %x, [2 x i64]* %notpod
   ret void
   ; CHECK: bl copy_notpod
   ; CHECK-NEXT: stp x0, x1, [{{.*}}]
 }
+
+; We shouldn't return the argument
+; when it has only inreg attribute
+define i64 @foobar(i64* inreg %0) {
+; CHECK-LABEL: foobar:
+; CHECK:       // %bb.0: // %entry
+; CHECK-NEXT:    ldr x0, [x0]
+; CHECK-NEXT:    ret
+entry:
+  %1 = load i64, i64* %0
+  ret i64 %1
+}