[analyzer] Handle [[assume(cond)]] as __builtin_assume(cond)

Resolves #100762

Author: vinay-deshmukh

clang/include/clang/StaticAnalyzer/Core/PathSensitive/ExprEngine.h

@@ -498,6 +498,10 @@ class ExprEngine {
   void VisitInitListExpr(const InitListExpr *E, ExplodedNode *Pred,
                          ExplodedNodeSet &Dst);
 
+  /// VisitAttributedStmt - Transfer function logic for AttributedStmt
+  void VisitAttributedStmt(const AttributedStmt *A, ExplodedNode *Pred,
+                           ExplodedNodeSet &Dst);
+
   /// VisitLogicalExpr - Transfer function logic for '&&', '||'
   void VisitLogicalExpr(const BinaryOperator* B, ExplodedNode *Pred,
                         ExplodedNodeSet &Dst);

clang/lib/Analysis/CFG.cpp

@@ -456,6 +456,36 @@ reverse_children::reverse_children(Stmt *S) {
                                 IE->getNumInits());
       return;
     }
+    case Stmt::AttributedStmtClass: {
+      AttributedStmt *attrStmt = cast<AttributedStmt>(S);
+      assert(attrStmt);
+
+      {
+        // for an attributed stmt, the "children()" returns only the NullStmt
+        // (;) but semantically the "children" are supposed to be the
+        // expressions _within_ i.e. the two square brackets i.e. [[ HERE ]]
+        // so we add the subexpressions first, _then_ add the "children"
+
+        for (const Attr *attr : attrStmt->getAttrs()) {
+
+          // i.e. one `assume()`
+          CXXAssumeAttr const *assumeAttr = llvm::dyn_cast<CXXAssumeAttr>(attr);
+          if (!assumeAttr) {
+            continue;
+          }
+          // Only handles [[ assume(<assumption>) ]] right now
+          Expr *assumption = assumeAttr->getAssumption();
+          childrenBuf.push_back(assumption);
+        }
+
+        // children() for an AttributedStmt is NullStmt(;)
+        llvm::append_range(childrenBuf, attrStmt->children());
+
+        // This needs to be done *after* childrenBuf has been populated.
+        children = childrenBuf;
+      }
+      return;
+    }
     default:
       break;
   }
@@ -2475,6 +2505,14 @@ static bool isFallthroughStatement(const AttributedStmt *A) {
   return isFallthrough;
 }
 
+static bool isCXXAssumeAttr(const AttributedStmt *A) {
+  bool hasAssumeAttr = hasSpecificAttr<CXXAssumeAttr>(A->getAttrs());
+
+  assert((!hasAssumeAttr || isa<NullStmt>(A->getSubStmt())) &&
+         "expected [[assume]] not to have children");
+  return hasAssumeAttr;
+}
+
 CFGBlock *CFGBuilder::VisitAttributedStmt(AttributedStmt *A,
                                           AddStmtChoice asc) {
   // AttributedStmts for [[likely]] can have arbitrary statements as children,
@@ -2490,6 +2528,11 @@ CFGBlock *CFGBuilder::VisitAttributedStmt(AttributedStmt *A,
     appendStmt(Block, A);
   }
 
+  if (isCXXAssumeAttr(A) && asc.alwaysAdd(*this, A)) {
+    autoCreateBlock();
+    appendStmt(Block, A);
+  }
+
   return VisitChildren(A);
 }
 

clang/lib/StaticAnalyzer/Core/ExprEngine.cpp

@@ -1946,7 +1946,6 @@ void ExprEngine::Visit(const Stmt *S, ExplodedNode *Pred,
     // to be explicitly evaluated.
     case Stmt::PredefinedExprClass:
     case Stmt::AddrLabelExprClass:
-    case Stmt::AttributedStmtClass:
     case Stmt::IntegerLiteralClass:
     case Stmt::FixedPointLiteralClass:
     case Stmt::CharacterLiteralClass:
@@ -1977,6 +1976,13 @@ void ExprEngine::Visit(const Stmt *S, ExplodedNode *Pred,
       break;
     }
 
+    case Stmt::AttributedStmtClass: {
+      Bldr.takeNodes(Pred);
+      VisitAttributedStmt(cast<AttributedStmt>(S), Pred, Dst);
+      Bldr.addNodes(Dst);
+      break;
+    }
+
     case Stmt::CXXDefaultArgExprClass:
     case Stmt::CXXDefaultInitExprClass: {
       Bldr.takeNodes(Pred);

clang/lib/StaticAnalyzer/Core/ExprEngineCXX.cpp

@@ -1200,3 +1200,30 @@ void ExprEngine::VisitLambdaExpr(const LambdaExpr *LE, ExplodedNode *Pred,
   // FIXME: Move all post/pre visits to ::Visit().
   getCheckerManager().runCheckersForPostStmt(Dst, Tmp, LE, *this);
 }
+
+void ExprEngine::VisitAttributedStmt(const AttributedStmt *A,
+                                     ExplodedNode *Pred, ExplodedNodeSet &Dst) {
+
+  ExplodedNodeSet CheckerPreStmt;
+  getCheckerManager().runCheckersForPreStmt(CheckerPreStmt, Pred, A, *this);
+
+  ExplodedNodeSet EvalSet;
+  StmtNodeBuilder Bldr(CheckerPreStmt, EvalSet, *currBldrCtx);
+
+  {
+    for (const auto *attr : A->getAttrs()) {
+
+      CXXAssumeAttr const *assumeAttr = llvm::dyn_cast<CXXAssumeAttr>(attr);
+      if (!assumeAttr) {
+        continue;
+      }
+      Expr *AssumeExpr = assumeAttr->getAssumption();
+
+      for (auto *node : CheckerPreStmt) {
+        Visit(AssumeExpr, node, EvalSet);
+      }
+    }
+  }
+
+  getCheckerManager().runCheckersForPostStmt(Dst, EvalSet, A, *this);
+}

clang/test/Analysis/out-of-bounds-new.cpp

@@ -180,3 +180,19 @@ int test_reference_that_might_be_after_the_end(int idx) {
   return ref;
 }
 
+// From: https://github.com/llvm/llvm-project/issues/100762
+extern int arr[10];
+void using_builtin(int x) {
+    __builtin_assume(x > 101); // CallExpr
+    arr[x] = 404; // expected-warning{{Out of bound access to memory}}
+}
+
+void using_assume_attr(int ax) {
+    [[assume(ax > 100)]]; // NullStmt with an attribute
+    arr[ax] = 405; // expected-warning{{Out of bound access to memory}}
+}
+
+void using_many_assume_attr(int yx) {
+    [[assume(yx > 104), assume(yx > 200), assume(yx < 300)]]; // NullStmt with an attribute
+    arr[yx] = 406; // expected-warning{{Out of bound access to memory}}
+}