Fix analyzer crash on 'StructuralValue' (llvm#79764)

`OpaqueValueExpr` doesn't necessarily contain a source expression.
Particularly, after llvm#78041, it is used to carry the type and the value
kind of a non-type template argument of floating-point type or referring
to a subobject (those are so called `StructuralValue` arguments).

This fixes llvm#79575.

(cherry picked from commit ef67f63)

clang/lib/Sema/SemaDecl.cpp

@@ -12752,7 +12752,8 @@ namespace {
       }
 
       if (OpaqueValueExpr *OVE = dyn_cast<OpaqueValueExpr>(E)) {
-        HandleValue(OVE->getSourceExpr());
+        if (Expr *SE = OVE->getSourceExpr())
+          HandleValue(SE);
         return;
       }
 

clang/lib/StaticAnalyzer/Core/Environment.cpp

@@ -40,8 +40,11 @@ static const Expr *ignoreTransparentExprs(const Expr *E) {
 
   switch (E->getStmtClass()) {
   case Stmt::OpaqueValueExprClass:
-    E = cast<OpaqueValueExpr>(E)->getSourceExpr();
-    break;
+    if (const Expr *SE = cast<OpaqueValueExpr>(E)->getSourceExpr()) {
+      E = SE;
+      break;
+    }
+    return E;
   case Stmt::ExprWithCleanupsClass:
     E = cast<ExprWithCleanups>(E)->getSubExpr();
     break;
@@ -98,7 +101,6 @@ SVal Environment::getSVal(const EnvironmentEntry &Entry,
   case Stmt::CXXBindTemporaryExprClass:
   case Stmt::ExprWithCleanupsClass:
   case Stmt::GenericSelectionExprClass:
-  case Stmt::OpaqueValueExprClass:
   case Stmt::ConstantExprClass:
   case Stmt::ParenExprClass:
   case Stmt::SubstNonTypeTemplateParmExprClass:

clang/test/Analysis/templates.cpp

@@ -68,3 +68,16 @@ namespace rdar13954714 {
   // force instantiation
   template void blockWithStatic<true>();
 }
+
+namespace structural_value_crash {
+  constexpr char abc[] = "abc";
+
+  template <const char* in>
+  void use_template_param() {
+    const char *p = in;
+  }
+
+  void force_instantiate() {
+    use_template_param<abc>();
+  }
+}

clang/test/SemaTemplate/temp_arg_nontype_cxx20.cpp

@@ -354,3 +354,20 @@ namespace ReportedRegression1 {
     return dummy.exit_code();
   }
 }
+
+namespace ReportedRegression2 {
+  const char str[] = "dummy";
+
+  struct S {
+    S operator+(const char*) const;
+  };
+
+  template <const char* in>
+  void fn() {
+    auto s = S{} + in;
+  }
+
+  void use() {
+    fn<str>();
+  }
+}