[clang] [analyzer] Suppress out of bounds reports after weak loop assumptions (PR #109804)

[Donát Nagy via cfe-commits]

================
@@ -2808,27 +2825,63 @@ void ExprEngine::processBranch(const Stmt *Condition,
       std::tie(StTrue, StFalse) = *KnownCondValueAssumption;
     else {
       assert(!isa<ObjCForCollectionStmt>(Condition));
+      // TODO: instead of this shortcut perhaps it would be better to "rejoin"
+      // the common execution path with
+      // StTrue = StFalse = PrevState;
       builder.generateNode(PrevState, true, PredN);
       builder.generateNode(PrevState, false, PredN);
       continue;
     }
     if (StTrue && StFalse)
       assert(!isa<ObjCForCollectionStmt>(Condition));
 
+    const Expr *EagerlyAssumeExpr =
+        PrevState->get<LastEagerlyAssumeAssumptionAt>();
+    const Expr *ConditionExpr = dyn_cast<Expr>(Condition);
+    if (ConditionExpr)
+      ConditionExpr = ConditionExpr->IgnoreParenCasts();
+    bool DidEagerlyAssume = EagerlyAssumeExpr == ConditionExpr;
+    bool BothFeasible = (DidEagerlyAssume || (StTrue && StFalse)) &&
+                        builder.isFeasible(true) && builder.isFeasible(false);
----------------
NagyDonat wrote:

The constructor of `BranchNodeBuilder` can also initialize the data members `InFeasibleTrue`/`InFeasibleFalse` to `true` (i.e. mark branches as infeasible) when respective `CFGBlock*`s `DstT` and `DstF` are null.

I didn't know exactly when does this happen, so I added the `isFeasible()` checks for the sake of safety.  

https://github.com/llvm/llvm-project/pull/109804