[clang] [clang][bytecode] Check for memcpy/memmove dummy pointers earlier (PR #121453)

[Timm Baeder via cfe-commits]

https://github.com/tbaederr created https://github.com/llvm/llvm-project/pull/121453

None

>From 9aeae2efcfb038af30f01a07eb8960a4a59929f9 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Timm=20B=C3=A4der?= <tbaeder at redhat.com>
Date: Thu, 2 Jan 2025 06:28:08 +0100
Subject: [PATCH] [clang][bytecode] Check for memcpy/memmove dummy pointers
 earlier

---
 clang/lib/AST/ByteCode/InterpBuiltin.cpp | 7 ++++---
 clang/test/CodeGen/builtin-memfns.c      | 1 +
 2 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/clang/lib/AST/ByteCode/InterpBuiltin.cpp b/clang/lib/AST/ByteCode/InterpBuiltin.cpp
index d0d8b03deab268..e9f3303f958d3e 100644
--- a/clang/lib/AST/ByteCode/InterpBuiltin.cpp
+++ b/clang/lib/AST/ByteCode/InterpBuiltin.cpp
@@ -1863,6 +1863,10 @@ static bool interp__builtin_memcpy(InterpState &S, CodePtr OpPC,
     return false;
   }
 
+  // Can't read from dummy pointers.
+  if (DestPtr.isDummy() || SrcPtr.isDummy())
+    return false;
+
   QualType DestElemType;
   size_t RemainingDestElems;
   if (DestPtr.getFieldDesc()->isArray()) {
@@ -1925,9 +1929,6 @@ static bool interp__builtin_memcpy(InterpState &S, CodePtr OpPC,
     }
   }
 
-  // As a last resort, reject dummy pointers.
-  if (DestPtr.isDummy() || SrcPtr.isDummy())
-    return false;
   assert(Size.getZExtValue() % DestElemSize == 0);
   if (!DoMemcpy(S, OpPC, SrcPtr, DestPtr, Bytes(Size.getZExtValue()).toBits()))
     return false;
diff --git a/clang/test/CodeGen/builtin-memfns.c b/clang/test/CodeGen/builtin-memfns.c
index 23c3c60b779b37..581eb85eb28e69 100644
--- a/clang/test/CodeGen/builtin-memfns.c
+++ b/clang/test/CodeGen/builtin-memfns.c
@@ -1,4 +1,5 @@
 // RUN: %clang_cc1 -triple i386-pc-linux-gnu -emit-llvm < %s| FileCheck %s
+// RUN: %clang_cc1 -triple i386-pc-linux-gnu -emit-llvm -fexperimental-new-constant-interpreter < %s| FileCheck %s
 
 typedef __WCHAR_TYPE__ wchar_t;
 typedef __SIZE_TYPE__ size_t;