1 files changed, 69 insertions, 0 deletions
diff --git a/llvm/lib/Target/X86/X86InstrInfo.cpp b/llvm/lib/Target/X86/X86InstrInfo.cpp
index 5e1a7528a16..d9a0897c24d 100644
--- a/llvm/lib/Target/X86/X86InstrInfo.cpp
+++ b/llvm/lib/Target/X86/X86InstrInfo.cpp
@@ -4029,6 +4029,75 @@ bool X86InstrInfo::isUnpredicatedTerminator(const MachineInstr &MI) const {
   return !isPredicated(MI);
 }
 
+bool X86InstrInfo::isUnconditionalTailCall(const MachineInstr &MI) const {
+  switch (MI.getOpcode()) {
+  case X86::TCRETURNdi:
+  case X86::TCRETURNri:
+  case X86::TCRETURNmi:
+  case X86::TCRETURNdi64:
+  case X86::TCRETURNri64:
+  case X86::TCRETURNmi64:
+    return true;
+  default:
+    return false;
+  }
+}
+
+bool X86InstrInfo::canMakeTailCallConditional(
+    SmallVectorImpl<MachineOperand> &BranchCond,
+    const MachineInstr &TailCall) const {
+  if (TailCall.getOpcode() != X86::TCRETURNdi) {
+    // Only direct calls can be done with a conditional branch.
+    return false;
+  }
+
+  assert(BranchCond.size() == 1);
+  if (BranchCond[0].getImm() > X86::LAST_VALID_COND) {
+    // Can't make a conditional tail call with this condition.
+    return false;
+  }
+
+  const X86MachineFunctionInfo *X86FI =
+      TailCall.getParent()->getParent()->getInfo<X86MachineFunctionInfo>();
+  if (X86FI->getTCReturnAddrDelta() != 0 ||
+      TailCall.getOperand(1).getImm() != 0) {
+    // A conditional tail call cannot do any stack adjustment.
+    return false;
+  }
+
+  return true;
+}
+
+void X86InstrInfo::replaceBranchWithTailCall(
+    MachineBasicBlock &MBB, SmallVectorImpl<MachineOperand> &BranchCond,
+    const MachineInstr &TailCall) const {
+  assert(canMakeTailCallConditional(BranchCond, TailCall));
+
+  MachineBasicBlock::iterator I = MBB.end();
+  while (I != MBB.begin()) {
+    --I;
+    if (I->isDebugValue())
+      continue;
+    if (!I->isBranch())
+      assert(0 && "Can't find the branch to replace!");
+
+    X86::CondCode CC = getCondFromBranchOpc(I->getOpcode());
+    assert(BranchCond.size() == 1);
+    if (CC != BranchCond[0].getImm())
+      continue;
+
+    break;
+  }
+
+  auto MIB = BuildMI(MBB, I, MBB.findDebugLoc(I), get(X86::TCRETURNdicc));
+  MIB->addOperand(TailCall.getOperand(0)); // Destination.
+  MIB.addImm(0); // Stack offset (not used).
+  MIB->addOperand(BranchCond[0]); // Condition.
+  MIB->addOperand(TailCall.getOperand(2)); // Regmask.
+
+  I->eraseFromParent();
+}
+
 // Given a MBB and its TBB, find the FBB which was a fallthrough MBB (it may
 // not be a fallthrough MBB now due to layout changes). Return nullptr if the
 // fallthrough MBB cannot be identified.