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

[Andrei Safronov via llvm-commits]

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@@ -51,76 +58,155 @@ void XtensaFrameLowering::emitPrologue(MachineFunction &MF,
   // Round up StackSize to 16*N
   StackSize += (16 - StackSize) & 0xf;
 
-  // No need to allocate space on the stack.
-  if (StackSize == 0 && !MFI.adjustsStack())
-    return;
-
-  // Adjust stack.
-  TII.adjustStackPtr(SP, -StackSize, MBB, MBBI);
-
-  // emit ".cfi_def_cfa_offset StackSize"
-  unsigned CFIIndex =
-      MF.addFrameInst(MCCFIInstruction::cfiDefCfaOffset(nullptr, StackSize));
-  BuildMI(MBB, MBBI, DL, TII.get(TargetOpcode::CFI_INSTRUCTION))
-      .addCFIIndex(CFIIndex);
-
-  const std::vector<CalleeSavedInfo> &CSI = MFI.getCalleeSavedInfo();
-
-  if (!CSI.empty()) {
-    // Find the instruction past the last instruction that saves a
-    // callee-saved register to the stack. The callee-saved store
-    // instructions are placed at the begin of basic block, so
-    //  iterate over instruction sequence and check that
-    // save instructions are placed correctly.
-    for (unsigned i = 0, e = CSI.size(); i < e; ++i) {
-#ifndef NDEBUG
-      const CalleeSavedInfo &Info = CSI[i];
-      int FI = Info.getFrameIdx();
-      int StoreFI = 0;
+  if (STI.isWindowedABI()) {
+    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.
+      MCRegister TmpReg = Xtensa::A8;
+
+      const XtensaInstrInfo &TII = *static_cast<const XtensaInstrInfo *>(
+          MBB.getParent()->getSubtarget().getInstrInfo());
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andreisfr wrote:

Thank you. Fixed.

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