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

[Anatoly Trosinenko via llvm-commits]

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@@ -425,6 +471,14 @@ Analysis::findGadgets(BinaryFunction &BF,
       MCInstReference Inst(&BB, I);
       const State &S = *PRA.getStateAt(Inst);
 
+      // If non-empty state was never propagated from the entry basic block
+      // to Inst, assume it to be unreachable and report a warning.
+      if (S.empty()) {
+        Result.Diagnostics.push_back(std::make_shared<GenericReport>(
+            Inst, "Warning: unreachable instruction found"));
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atrosinenko wrote:

My initial intention was not to skip instructions silently (in case it is skipped due to some error in PacRetAnalysis). On one hand, this should be caught by the tests, on the other hand, this warning helps implementing the tests. Anyway, this should be trivial to remove this warning later.

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