[compiler-rt] [flang] [llvm] [AArch64] fix trampoline implementation: use X15 (PR #126743)

[Eli Friedman via llvm-commits]

================
@@ -1982,6 +1982,27 @@ void AArch64FrameLowering::emitPrologue(MachineFunction &MF,
           : 0;
 
   if (windowsRequiresStackProbe(MF, NumBytes + RealignmentPadding)) {
+    // Find an available register to spill the value of X15 to, if X15 is being
+    // used already for nest.
+    unsigned X15Scratch = AArch64::NoRegister;
+    const AArch64Subtarget &STI = MF.getSubtarget<AArch64Subtarget>();
+    if (llvm::any_of(MBB.liveins(),
+                     [&STI](const MachineBasicBlock::RegisterMaskPair &LiveIn) {
+                       return STI.getRegisterInfo()->isSuperOrSubRegisterEq(
+                           AArch64::X15, LiveIn.PhysReg);
+                     })) {
+      X15Scratch = findScratchNonCalleeSaveRegister(&MBB);
----------------
efriedma-quic wrote:

We need to make sure the scratch is not x16 or x17.  (See CSR_AArch64_StackProbe_Windows.)

https://github.com/llvm/llvm-project/pull/126743