[llvm] [BOLT] Gadget scanner: analyze functions without CFG information (PR #133461)

[Kristof Beyls via llvm-commits]

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@@ -124,6 +124,27 @@ class TrackedRegisters {
   }
 };
 
+// Without CFG, we reset gadget scanning state when encountering an
+// unconditional branch. Note that BC.MIB->isUnconditionalBranch neither
+// considers indirect branches nor annotated tail calls as unconditional.
+static bool isStateTrackingBoundary(const BinaryContext &BC,
+                                    const MCInst &Inst) {
+  const MCInstrDesc &Desc = BC.MII->get(Inst.getOpcode());
+  // Adapted from llvm::MCInstrDesc::isUnconditionalBranch().
+  return Desc.isBranch() && Desc.isBarrier();
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kbeyls wrote:

I wonder if what you're really after here is only checking for `Desc.isBarrier()`, because the documentation for `isBarrier` says:
```
/// Returns true if the specified instruction stops control flow
/// from executing the instruction immediately following it.  Examples include
/// unconditional branches and return instructions.
```

Another example I encountered in real-world binaries for AArch64 is the `brk` instruction...

https://github.com/llvm/llvm-project/pull/133461