[llvm] [AArch64][SVE] Remove isSVECC() in favour of changing the calling convention (PR #152742)

[Sander de Smalen via llvm-commits]

================
@@ -7837,24 +7838,44 @@ SDValue AArch64TargetLowering::LowerFormalArguments(
     const SmallVectorImpl<ISD::InputArg> &Ins, const SDLoc &DL,
     SelectionDAG &DAG, SmallVectorImpl<SDValue> &InVals) const {
   MachineFunction &MF = DAG.getMachineFunction();
-  const Function &F = MF.getFunction();
+  Function &F = MF.getFunction();
   MachineFrameInfo &MFI = MF.getFrameInfo();
   bool IsWin64 =
       Subtarget->isCallingConvWin64(F.getCallingConv(), F.isVarArg());
   bool StackViaX4 = CallConv == CallingConv::ARM64EC_Thunk_X64 ||
                     (isVarArg && Subtarget->isWindowsArm64EC());
   AArch64FunctionInfo *FuncInfo = MF.getInfo<AArch64FunctionInfo>();
 
-  SmallVector<ISD::OutputArg, 4> Outs;
-  GetReturnInfo(CallConv, F.getReturnType(), F.getAttributes(), Outs,
-                DAG.getTargetLoweringInfo(), MF.getDataLayout());
-  if (any_of(Outs, [](ISD::OutputArg &Out){ return Out.VT.isScalableVector(); }))
-    FuncInfo->setIsSVECC(true);
-
   // Assign locations to all of the incoming arguments.
   SmallVector<CCValAssign, 16> ArgLocs;
   CCState CCInfo(CallConv, isVarArg, MF, ArgLocs, *DAG.getContext());
 
+  // This logic is consistent with AArch64TargetLowering::LowerCall.
+  // The `ShouldUpgradeToSVECC` flag can be when analyzing arguments.
+  bool ShouldUpgradeToSVECC = false;
+  auto _ = make_scope_exit([&] {
+    if (CallConv != CallingConv::C && CallConv != CallingConv::Fast)
+      return;
+
+    if (!ShouldUpgradeToSVECC) {
+      // If the flag was not set, check if the return value requires the SVE CC.
+      SmallVector<ISD::OutputArg, 4> Outs;
+      GetReturnInfo(CallConv, F.getReturnType(), F.getAttributes(), Outs,
+                    DAG.getTargetLoweringInfo(), MF.getDataLayout());
+      ShouldUpgradeToSVECC = any_of(
+          Outs, [](ISD::OutputArg &Out) { return Out.VT.isScalableVector(); });
+    }
+
+    if (!ShouldUpgradeToSVECC)
+      return;
+
+    if (isVarArg)
+      report_fatal_error("Passing/returning SVE types to variadic functions "
+                         "is currently not supported");
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sdesmalen-arm wrote:

You can pass them to variadic functions, but not as variadic arguments.

https://github.com/llvm/llvm-project/pull/152742