[analyzer] Add support for consteval in ConditionBRVisitor::VisitTerminator (#146859)

Fix crash when ConditionBRVisitor::VisitTerminator is faced with `if
consteval` which doesn't have the expected traditional condition

Fixes #139130

Author: imdj

clang/lib/StaticAnalyzer/Core/BugReporterVisitors.cpp

@@ -2793,9 +2793,14 @@ PathDiagnosticPieceRef ConditionBRVisitor::VisitTerminator(
   // more tricky because there are more than two branches to account for.
   default:
     return nullptr;
-  case Stmt::IfStmtClass:
-    Cond = cast<IfStmt>(Term)->getCond();
+  case Stmt::IfStmtClass: {
+    const auto *IfStatement = cast<IfStmt>(Term);
+    // Handle if consteval which doesn't have a traditional condition.
+    if (IfStatement->isConsteval())
+      return nullptr;
+    Cond = IfStatement->getCond();
     break;
+  }
   case Stmt::ConditionalOperatorClass:
     Cond = cast<ConditionalOperator>(Term)->getCond();
     break;

clang/test/Analysis/consteval-if.cpp

@@ -0,0 +1,16 @@
+// RUN: %clang_analyze_cc1 -std=c++23 -analyzer-checker=core -verify %s
+// RUN: %clang_analyze_cc1 -std=c++26 -analyzer-checker=core -verify %s
+
+void test_consteval() {
+  if consteval {
+    int *ptr = nullptr;
+    *ptr = 42; // expected-warning{{Dereference of null pointer (loaded from variable 'ptr')}}
+  }
+}
+
+void test_not_consteval() {
+  if !consteval {
+    int *ptr = nullptr;
+    *ptr = 42; // expected-warning{{Dereference of null pointer (loaded from variable 'ptr')}}
+  }
+}