[llvm] [BOLT] Gadget scanner: reformulate the state for data-flow analysis (PR #131898)

[Anatoly Trosinenko via llvm-commits]

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@@ -551,6 +551,16 @@ class MCPlusBuilder {
     return Analysis->isReturn(Inst);
   }
 
+  /// Returns the registers that are trusted at function entry.
+  ///
+  /// Each register should be treated as if a successfully authenticated
+  /// pointer was written to it before entering the function (i.e. the
+  /// pointer is safe to jump to as well as to be signed).
+  virtual SmallVector<MCPhysReg> getTrustedLiveInRegs() const {
+    llvm_unreachable("not implemented");
+    return {};
+  }
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atrosinenko wrote:

It looks like the set of registers returned by `getTrustedLiveInRegs` on AArch64 can be derived from the fact that LR is set by branch-with-link instructions. To some extent, this does look more like a property of the ABI, but as far as I can see target-specific hooks are placed either to `lib/Target/XYZ/XYZMCPlusBuilder.cpp` or to `lib/Target/XYZ/XYZMCSymbolizer.(h|cpp)`, so there doesn't seem to be many places where such target-specific hook can be defined.

https://github.com/llvm/llvm-project/pull/131898