[TailDuplicator] Determine if computed gotos using blockaddress (#132536)

Using `blockaddress` should be more reliable than determining if an
operand comes from a jump table index.

Alternative: Add the `MachineInstr::MIFlag::ComputedGoto` flag when
lowering `indirectbr`. But I don't think this approach is suitable to
backport.

(cherry picked from commit 66f158d)

Author: dianqk

llvm/include/llvm/CodeGen/MachineBasicBlock.h

@@ -311,6 +311,15 @@ class MachineBasicBlock
   const MachineFunction *getParent() const { return xParent; }
   MachineFunction *getParent() { return xParent; }
 
+  /// Returns true if the original IR terminator is an `indirectbr`. This
+  /// typically corresponds to a `goto` in C, rather than jump tables.
+  bool terminatorIsComputedGoto() const {
+    return back().isIndirectBranch() &&
+           llvm::all_of(successors(), [](const MachineBasicBlock *Succ) {
+             return Succ->isIRBlockAddressTaken();
+           });
+  }
+
   using instr_iterator = Instructions::iterator;
   using const_instr_iterator = Instructions::const_iterator;
   using reverse_instr_iterator = Instructions::reverse_iterator;

llvm/lib/CodeGen/TailDuplicator.cpp

@@ -604,7 +604,7 @@ bool TailDuplicator::shouldTailDuplicate(bool IsSimple,
   bool HasComputedGoto = false;
   if (!TailBB.empty()) {
     HasIndirectbr = TailBB.back().isIndirectBranch();
-    HasComputedGoto = TailBB.back().isComputedGoto();
+    HasComputedGoto = TailBB.terminatorIsComputedGoto();
   }
 
   if (HasIndirectbr && PreRegAlloc)