[clang] [clang][bytecode] Check for invalid function decls (PR #175312)

[Timm Baeder via cfe-commits]

https://github.com/tbaederr created https://github.com/llvm/llvm-project/pull/175312

If the function decl is invalid, the `interp::Function` shouldn't ever be valid.

Fixes https://github.com/llvm/llvm-project/issues/175280

>From cce5595f181e93d6da5e7643d1fe7531a8b9f564 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Timm=20B=C3=A4der?= <tbaeder at redhat.com>
Date: Sat, 10 Jan 2026 16:02:23 +0100
Subject: [PATCH] [clang][bytecode] Check for invalid function decls

If the function decl is invalid, the `interp::Function` shouldn't ever
be valid.

Fixes https://github.com/llvm/llvm-project/issues/175280
---
 clang/lib/AST/ByteCode/ByteCodeEmitter.cpp | 3 ++-
 clang/lib/AST/ByteCode/Function.h          | 5 +++--
 clang/test/AST/ByteCode/invalid.cpp        | 9 +++++++++
 3 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/clang/lib/AST/ByteCode/ByteCodeEmitter.cpp b/clang/lib/AST/ByteCode/ByteCodeEmitter.cpp
index ed743768d077e..f430b2329a6f3 100644
--- a/clang/lib/AST/ByteCode/ByteCodeEmitter.cpp
+++ b/clang/lib/AST/ByteCode/ByteCodeEmitter.cpp
@@ -86,7 +86,8 @@ void ByteCodeEmitter::compileFunc(const FunctionDecl *FuncDecl,
 
   // Set the function's code.
   Func->setCode(FuncDecl, NextLocalOffset, std::move(Code), std::move(SrcMap),
-                std::move(Scopes), FuncDecl->hasBody());
+                std::move(Scopes), FuncDecl->hasBody(),
+                !FuncDecl->isInvalidDecl());
   Func->setIsFullyCompiled(true);
 }
 
diff --git a/clang/lib/AST/ByteCode/Function.h b/clang/lib/AST/ByteCode/Function.h
index 80283afb6e987..a086682d4ce21 100644
--- a/clang/lib/AST/ByteCode/Function.h
+++ b/clang/lib/AST/ByteCode/Function.h
@@ -240,13 +240,14 @@ class Function final {
   /// Sets the code of a function.
   void setCode(FunctionDeclTy Source, unsigned NewFrameSize,
                llvm::SmallVector<std::byte> &&NewCode, SourceMap &&NewSrcMap,
-               llvm::SmallVector<Scope, 2> &&NewScopes, bool NewHasBody) {
+               llvm::SmallVector<Scope, 2> &&NewScopes, bool NewHasBody,
+               bool NewIsValid) {
     this->Source = Source;
     FrameSize = NewFrameSize;
     Code = std::move(NewCode);
     SrcMap = std::move(NewSrcMap);
     Scopes = std::move(NewScopes);
-    IsValid = true;
+    IsValid = NewIsValid;
     HasBody = NewHasBody;
   }
 
diff --git a/clang/test/AST/ByteCode/invalid.cpp b/clang/test/AST/ByteCode/invalid.cpp
index 541aa634007e3..f7f2da2769d65 100644
--- a/clang/test/AST/ByteCode/invalid.cpp
+++ b/clang/test/AST/ByteCode/invalid.cpp
@@ -123,3 +123,12 @@ namespace InvalidIntPtrRecord {
   };
   Size_t foo() { return (Size_t)(&((struct S *)0)->a); }
 }
+
+namespace RetVoidInInvalidFunc {
+
+  constexpr bool foo() { return; } // both-error {{non-void constexpr function 'foo' should return a value}}
+  template <int N> struct X {
+    int v = N;
+  };
+  X<foo()> x; // both-error {{non-type template argument is not a constant expression}}
+}