[llvm] [RISCV] Stack clash protection for dynamic alloca (PR #122508)

[Craig Topper via llvm-commits]

================
@@ -22559,3 +22564,101 @@ unsigned RISCVTargetLowering::getStackProbeSize(const MachineFunction &MF,
   StackProbeSize = alignDown(StackProbeSize, StackAlign.value());
   return StackProbeSize ? StackProbeSize : StackAlign.value();
 }
+
+SDValue RISCVTargetLowering::LowerDYNAMIC_STACKALLOC(SDValue Op,
+                                                     SelectionDAG &DAG) const {
+  MachineFunction &MF = DAG.getMachineFunction();
+  if (!hasInlineStackProbe(MF))
+    return SDValue();
+
+  MVT XLenVT = Subtarget.getXLenVT();
+  // Get the inputs.
+  SDNode *Node = Op.getNode();
+  SDValue Chain = Op.getOperand(0);
+  SDValue Size = Op.getOperand(1);
+
+  MaybeAlign Align =
+      cast<ConstantSDNode>(Op.getOperand(2))->getMaybeAlignValue();
+  SDLoc dl(Op);
+  EVT VT = Node->getValueType(0);
+
+  // Construct the new SP value in a GPR.
+  SDValue SP = DAG.getCopyFromReg(Chain, dl, RISCV::X2, XLenVT);
+  Chain = SP.getValue(1);
+  SP = DAG.getNode(ISD::SUB, dl, XLenVT, SP, Size);
+  if (Align)
+    SP = DAG.getNode(ISD::AND, dl, VT, SP.getValue(0),
+                     DAG.getSignedConstant(-(uint64_t)Align->value(), dl, VT));
+
+  // Set the real SP to the new value with a probing loop.
+  Chain = DAG.getNode(RISCVISD::PROBED_ALLOCA, dl, MVT::Other, Chain, SP);
+  SDValue Ops[2] = {SP, Chain};
+  return DAG.getMergeValues(Ops, dl);
----------------
topperc wrote:

`DAG.getMergeValues({SP, Chain}, dl);` No need for the array.

https://github.com/llvm/llvm-project/pull/122508