[clang] [Wunsafe-buffer-usage] False positives for & expression indexing constant size array (arr[anything & 0]) (PR #112284)

[Ziqing Luo via cfe-commits]

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@@ -431,6 +431,122 @@ AST_MATCHER(CXXConstructExpr, isSafeSpanTwoParamConstruct) {
   return false;
 }
 
+class MaxValueEval : public ConstStmtVisitor<MaxValueEval, llvm::APInt> {
+
+  ASTContext &Context;
+  llvm::APInt Max;
+  unsigned bit_width;
+
+public:
+  typedef ConstStmtVisitor<MaxValueEval, llvm::APInt> VisitorBase;
+
+  explicit MaxValueEval(ASTContext &Ctx, const Expr *exp) : Context(Ctx) {
+    bit_width = Ctx.getIntWidth(exp->getType());
+    Max = llvm::APInt::getSignedMaxValue(bit_width);
+    // val.clear();
+  }
+
+  llvm::APInt findMatch(Expr *exp) { return TraverseStmt(exp); }
+
+  llvm::APInt TraverseStmt(Stmt *S) {
+    if (Expr *E = dyn_cast<Expr>(S)) {
+      Expr::EvalResult EVResult;
+      if (ImplicitCastExpr *ICE = dyn_cast<ImplicitCastExpr>(E)) {
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ziqingluo-90 wrote:

nit: we could do a `switch` on `E->getStmtClass()` here, which is more efficient than a list of if-else.

https://github.com/llvm/llvm-project/pull/112284