[llvm-branch-commits] [llvm] [BOLT][BTI] Add MCPlusBuilder::addBTItoBBStart (PR #167329)

[Gergely Bálint via llvm-branch-commits]

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@@ -2781,6 +2781,81 @@ class AArch64MCPlusBuilder : public MCPlusBuilder {
     Inst.addOperand(MCOperand::createImm(HintNum));
   }
 
+  bool isBTIVariantCoveringCall(MCInst &Call, MCInst &Pad) const override {
+    assert((isIndirectCall(Call) || isIndirectBranch(Call)) &&
+           "Not an indirect call or branch.");
+
+    // A BLR can be accepted by a BTI c.
+    if (isIndirectCall(Call))
+      return isBTILandingPad(Pad, true, false) ||
+             isBTILandingPad(Pad, true, true);
+
+    // A BR can be accepted by a BTI j or BTI c (and BTI jc) IF the operand is
+    // x16 or x17. If the operand is not x16 or x17, it can be accepted by a BTI
+    // j or BTI jc (and not BTI c).
+    if (isIndirectBranch(Call)) {
+      assert(Call.getNumOperands() == 1 &&
+             "Indirect branch needs to have 1 operand.");
+      assert(Call.getOperand(0).isReg() &&
+             "Indirect branch does not have a register operand.");
+      MCPhysReg Reg = Call.getOperand(0).getReg();
+      if (Reg == AArch64::X16 || Reg == AArch64::X17)
+        return isBTILandingPad(Pad, true, false) ||
+               isBTILandingPad(Pad, false, true) ||
+               isBTILandingPad(Pad, true, true);
+      return isBTILandingPad(Pad, false, true) ||
+             isBTILandingPad(Pad, true, true);
+    }
+    return false;
+  }
+
+  void addBTItoBBStart(BinaryBasicBlock &BB, MCInst &Call) const override {
+    auto II = BB.getFirstNonPseudo();
+    if (II != BB.end()) {
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bgergely0 wrote:

I think I have previously encountered empty BasicBlocks - that was around function splitting I believe. Not sure if empty BasicBlocks should be covered here.  Currently, we silently skip them - that does not seem ideal.

https://github.com/llvm/llvm-project/pull/167329