[clang] [-Wunsafe-buffer-usage] Fix false positives for constant cases (PR #92432)

[via cfe-commits]

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@@ -420,25 +420,63 @@ AST_MATCHER(ArraySubscriptExpr, isSafeArraySubscript) {
   //    already duplicated
   //  - call both from Sema and from here
 
-  const auto *BaseDRE =
-      dyn_cast<DeclRefExpr>(Node.getBase()->IgnoreParenImpCasts());
-  if (!BaseDRE)
+  if (const auto *BaseDRE =
+          dyn_cast<DeclRefExpr>(Node.getBase()->IgnoreParenImpCasts())) {
+    if (!BaseDRE->getDecl())
+      return false;
+    if (const auto *CATy = Finder->getASTContext().getAsConstantArrayType(
+            BaseDRE->getDecl()->getType())) {
+      if (const auto *IdxLit = dyn_cast<IntegerLiteral>(Node.getIdx())) {
+        const APInt ArrIdx = IdxLit->getValue();
+        // FIXME: ArrIdx.isNegative() we could immediately emit an error as
+        // that's a bug
+        if (ArrIdx.isNonNegative() &&
+            ArrIdx.getLimitedValue() < CATy->getLimitedSize())
+          return true;
+      }
+    }
+  }
+
+  if (const auto *BaseSL =
+          dyn_cast<StringLiteral>(Node.getBase()->IgnoreParenImpCasts())) {
+    if (const auto *CATy =
+            Finder->getASTContext().getAsConstantArrayType(BaseSL->getType())) {
+      if (const auto *IdxLit = dyn_cast<IntegerLiteral>(Node.getIdx())) {
+        const APInt ArrIdx = IdxLit->getValue();
+        // FIXME: ArrIdx.isNegative() we could immediately emit an error as
+        // that's a bug
+        if (ArrIdx.isNonNegative() &&
+            ArrIdx.getLimitedValue() < CATy->getLimitedSize())
+          return true;
+      }
+    }
+  }
+
+  return false;
+}
+
+AST_MATCHER(BinaryOperator, isSafePtrArithmetic) {
+  if (Node.getOpcode() != BinaryOperatorKind::BO_Add)
     return false;
-  if (!BaseDRE->getDecl())
+
+  const auto *LHSDRE = dyn_cast<DeclRefExpr>(Node.getLHS()->IgnoreImpCasts());
+  if (!LHSDRE)
     return false;
+
   const auto *CATy = Finder->getASTContext().getAsConstantArrayType(
-      BaseDRE->getDecl()->getType());
+      LHSDRE->getDecl()->getType());
   if (!CATy)
     return false;
 
-  if (const auto *IdxLit = dyn_cast<IntegerLiteral>(Node.getIdx())) {
-    const APInt ArrIdx = IdxLit->getValue();
-    // FIXME: ArrIdx.isNegative() we could immediately emit an error as that's a
-    // bug
-    if (ArrIdx.isNonNegative() &&
-        ArrIdx.getLimitedValue() < CATy->getLimitedSize())
-      return true;
-  }
+  const auto *RHSIntLit = dyn_cast<IntegerLiteral>(Node.getRHS());
+  if (!RHSIntLit)
+    return false;
+
+  const APInt BufferOffset = RHSIntLit->getValue();
+
+  if (BufferOffset.isNonNegative() &&
----------------
jkorous-apple wrote:

Feel free to file issues but at this point I think it's not a good use of our time because only the very trivial case gets recognized.
Ultimately the cases that should be supported are likely to be found in Sema tests for the functionality referred to by the FIXME above.

https://github.com/llvm/llvm-project/pull/92432