[llvm] Xtensa] Implement windowed call ABI. (PR #130001)

[Matt Arsenault via llvm-commits]

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@@ -51,6 +58,83 @@ void XtensaFrameLowering::emitPrologue(MachineFunction &MF,
   // Round up StackSize to 16*N
   StackSize += (16 - StackSize) & 0xf;
 
+  if (STI.isWinABI()) {
+    StackSize += 32;
+    uint64_t MaxAlignment = MFI.getMaxAlign().value();
+    if(MaxAlignment > 32)
+      StackSize += MaxAlignment;
+
+    if (StackSize <= 32760) {
+      BuildMI(MBB, MBBI, DL, TII.get(Xtensa::ENTRY))
+          .addReg(SP)
+          .addImm(StackSize);
+    } else {
+      /* Use a8 as a temporary since a0-a7 may be live.  */
+      unsigned TmpReg = Xtensa::A8;
+
+      const XtensaInstrInfo &TII = *static_cast<const XtensaInstrInfo *>(
+          MBB.getParent()->getSubtarget().getInstrInfo());
+      BuildMI(MBB, MBBI, DL, TII.get(Xtensa::ENTRY))
+          .addReg(SP)
+          .addImm(MIN_FRAME_SIZE);
+      TII.loadImmediate(MBB, MBBI, &TmpReg, StackSize - MIN_FRAME_SIZE);
+      BuildMI(MBB, MBBI, DL, TII.get(Xtensa::SUB), TmpReg)
+          .addReg(SP)
+          .addReg(TmpReg);
+      BuildMI(MBB, MBBI, DL, TII.get(Xtensa::MOVSP), SP).addReg(TmpReg);
+    }
+
+    // Calculate how much is needed to have the correct alignment.
+    // Change offset to: alignment + difference.
+    // For example, in case of alignment of 128:
+    // diff_to_128_aligned_address = (128 - (SP & 127))
+    // new_offset = SP + diff_to_128_aligned_address
+    // This is safe to do because we increased the stack size by MaxAlignment.
+    unsigned Reg, RegMisAlign;
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arsenm wrote:

Use MCRegister type 

https://github.com/llvm/llvm-project/pull/130001