[clang] [llvm] [AArch64] Stack probing for function prologues (PR #66524)

[Momchil Velikov via llvm-commits]

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@@ -1827,12 +1908,36 @@ void AArch64FrameLowering::emitPrologue(MachineFunction &MF,
       // FIXME: in the case of dynamic re-alignment, NumBytes doesn't have
       // the correct value here, as NumBytes also includes padding bytes,
       // which shouldn't be counted here.
-      emitFrameOffset(
-          MBB, MBBI, DL, scratchSPReg, AArch64::SP,
-          StackOffset::getFixed(-NumBytes), TII, MachineInstr::FrameSetup,
-          false, NeedsWinCFI, &HasWinCFI, EmitAsyncCFI && !HasFP,
+      StackOffset CFAOffset =
           SVEStackSize +
-              StackOffset::getFixed((int64_t)MFI.getStackSize() - NumBytes));
+          StackOffset::getFixed((int64_t)MFI.getStackSize() - NumBytes);
+      if (NeedsStackProbe && !NeedsRealignment) {
+        // If we don't need to re-align the stack, we can use a more efficient
+        // sequence for stack probing.
+        Register ScratchReg = findScratchNonCalleeSaveRegister(&MBB);
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momchil-velikov wrote:

Because we may issue a loop when replacing `PROBED_STACKALLOC` and that loop uses a scratch register (containing the new `SP` value) in the loop exit condition.

https://github.com/llvm/llvm-project/pull/66524