[AArch64][Outliner] Don't outline BTI instructions

[olista01]

Summary

We can't outline BTI instructions, because they need to be the very first instruction executed after an indirect call or branch. If we outline them, then an indirect call might go to the branch to the outlined function, which will fault.

llvm/trunk/lib/Target/AArch64/AArch64InstrInfo.cpp

AArch64InstrInfo::getOutliningType(MachineBasicBlock::iterator &MIT,
   if (MI.isPosition())
     return outliner::InstrType::Illegal;
 
   // Don't touch the link register or W30.
   if (MI.readsRegister(AArch64::W30, &getRegisterInfo()) ||
       MI.modifiesRegister(AArch64::W30, &getRegisterInfo()))
     return outliner::InstrType::Illegal;
 
+  // Don't outline BTI instructions, because that will prevent the outlining
+  // site from being indirectly callable.
+  if (MI.getOpcode() == AArch64::HINT) {
+    int64_t Imm = MI.getOperand(0).getImm();
+    if (Imm == 32 || Imm == 34 || Imm == 36 || Imm == 38)
+      return outliner::InstrType::Illegal;
+  }
+
   return outliner::InstrType::Legal;
 }
 
 void AArch64InstrInfo::fixupPostOutline(MachineBasicBlock &MBB) const {
   for (MachineInstr &MI : MBB) {
     MachineOperand *Base;
     unsigned Width;
     int64_t Offset;

llvm/trunk/test/CodeGen/AArch64/machine-outliner-outline-bti.ll

+; RUN: llc -mtriple aarch64--none-eabi < %s | FileCheck %s
+
+; The BTI instruction cannot be outlined, because it needs to be the very first
+; instruction executed after an indirect call.
+
+@g = hidden global i32 0, align 4
+
+define hidden void @foo() minsize "branch-target-enforcement" {
+entry:
+; CHECK: hint #34
+; CHECK: b       OUTLINED_FUNCTION_0
+  store volatile i32 1, i32* @g, align 4
+  ret void
+}
+
+define hidden void @bar() minsize "branch-target-enforcement" {
+entry:
+; CHECK: hint #34
+; CHECK: b       OUTLINED_FUNCTION_0
+  store volatile i32 1, i32* @g, align 4
+  ret void
+}