[llvm] [RISC-V] Fix crash with late stack realignment requirement (PR #83496)

[Nemanja Ivanovic via llvm-commits]

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@@ -1175,6 +1178,35 @@ static unsigned estimateFunctionSizeInBytes(const MachineFunction &MF,
   return FnSize;
 }
 
+Align RISCVFrameLowering::maxPossibleSpillAlign(
+    const MachineFunction &MF) const {
+  if (MaxSpillAlign.contains(&MF))
+    return MaxSpillAlign.at(&MF);
+
+  const MachineRegisterInfo &MRI = MF.getRegInfo();
+  const TargetRegisterInfo *TRI = MF.getSubtarget().getRegisterInfo();
+  Align CurrMaxAlign = Align(1);
+  // The maximum spill alignment has not yet been computed. Compute it.
+  for (const MachineBasicBlock &MBB : MF) {
+    for (const MachineInstr &MI : MBB) {
+      for (const MachineOperand &MO : MI.operands()) {
+        if (!MO.isReg())
+          continue;
+        Register Reg = MO.getReg();
+        const TargetRegisterClass *RC;
+        if (Reg.isPhysical())
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nemanjai wrote:

Strictly speaking, this is not needed to resolve the observed problem as we won't insert a spill of a physical register. However, I implemented it this way to catch any use that might require a realignment - I guess a paranoid position.

https://github.com/llvm/llvm-project/pull/83496