[clang-tidy] fix crash in altera-id-dependent-backward-branch (#113833)

Add some checks for `nullptr` and change some `dyn_cast` to
`dyn_cast_if_present` to avoid crashes.

Fixes #55408

clang-tools-extra/clang-tidy/altera/IdDependentBackwardBranchCheck.cpp

@@ -78,16 +78,22 @@ void IdDependentBackwardBranchCheck::registerMatchers(MatchFinder *Finder) {
 
 IdDependentBackwardBranchCheck::IdDependencyRecord *
 IdDependentBackwardBranchCheck::hasIdDepVar(const Expr *Expression) {
+  if (!Expression)
+    return nullptr;
+
   if (const auto *Declaration = dyn_cast<DeclRefExpr>(Expression)) {
     // It is a DeclRefExpr, so check if it's an ID-dependent variable.
-    const auto *CheckVariable = dyn_cast<VarDecl>(Declaration->getDecl());
+    const auto *CheckVariable =
+        dyn_cast_if_present<VarDecl>(Declaration->getDecl());
+    if (!CheckVariable)
+      return nullptr;
     auto FoundVariable = IdDepVarsMap.find(CheckVariable);
     if (FoundVariable == IdDepVarsMap.end())
       return nullptr;
     return &(FoundVariable->second);
   }
   for (const auto *Child : Expression->children())
-    if (const auto *ChildExpression = dyn_cast<Expr>(Child))
+    if (const auto *ChildExpression = dyn_cast_if_present<Expr>(Child))
       if (IdDependencyRecord *Result = hasIdDepVar(ChildExpression))
         return Result;
   return nullptr;
@@ -95,16 +101,21 @@ IdDependentBackwardBranchCheck::hasIdDepVar(const Expr *Expression) {
 
 IdDependentBackwardBranchCheck::IdDependencyRecord *
 IdDependentBackwardBranchCheck::hasIdDepField(const Expr *Expression) {
+  if (!Expression)
+    return nullptr;
+
   if (const auto *MemberExpression = dyn_cast<MemberExpr>(Expression)) {
     const auto *CheckField =
-        dyn_cast<FieldDecl>(MemberExpression->getMemberDecl());
+        dyn_cast_if_present<FieldDecl>(MemberExpression->getMemberDecl());
+    if (!CheckField)
+      return nullptr;
     auto FoundField = IdDepFieldsMap.find(CheckField);
     if (FoundField == IdDepFieldsMap.end())
       return nullptr;
     return &(FoundField->second);
   }
   for (const auto *Child : Expression->children())
-    if (const auto *ChildExpression = dyn_cast<Expr>(Child))
+    if (const auto *ChildExpression = dyn_cast_if_present<Expr>(Child))
       if (IdDependencyRecord *Result = hasIdDepField(ChildExpression))
         return Result;
   return nullptr;

clang-tools-extra/docs/ReleaseNotes.rst

@@ -147,6 +147,10 @@ New check aliases
 Changes in existing checks
 ^^^^^^^^^^^^^^^^^^^^^^^^^^
 
+- Improved :doc:`altera-id-dependent-backward-branch
+  <clang-tidy/checks/altera/id-dependent-backward-branch>` check by fixing
+  crashes from invalid code.
+
 - Improved :doc:`bugprone-casting-through-void
   <clang-tidy/checks/bugprone/casting-through-void>` check to suggest replacing
   the offending code with ``reinterpret_cast``, to more clearly express intent.

clang-tools-extra/test/clang-tidy/checkers/altera/id-dependent-backward-branch.cpp

@@ -1,4 +1,4 @@
-// RUN: %check_clang_tidy %s altera-id-dependent-backward-branch %t -- -header-filter=.* "--" -cl-std=CL1.2 -c
+// RUN: %check_clang_tidy %s altera-id-dependent-backward-branch %t -- -header-filter=.* "--" -cl-std=CLC++1.0 -c
 
 void error() {
   // ==== Conditional Expressions ====
@@ -80,3 +80,9 @@ void success() {
     }
   }
 }
+
+template<char... STOP>
+void gh55408(char const input[], int pos) {
+  while (((input[pos] != STOP) && ...));
+}
+