[clang] [clang][bytecode] Handle reads on zero-size arrays (PR #152706)

[Timm Baeder via cfe-commits]

https://github.com/tbaederr created https://github.com/llvm/llvm-project/pull/152706

None

>From 328fa47105c81b659e059e9be93c75a32a30fd28 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Timm=20B=C3=A4der?= <tbaeder at redhat.com>
Date: Fri, 8 Aug 2025 14:18:45 +0200
Subject: [PATCH] [clang][bytecode] Handle reads on zero-size arrays

---
 clang/lib/AST/ByteCode/Interp.cpp  |  4 +---
 clang/test/AST/ByteCode/arrays.cpp | 13 +++++++++++++
 2 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/clang/lib/AST/ByteCode/Interp.cpp b/clang/lib/AST/ByteCode/Interp.cpp
index bc14bd3d1bb99..b5c044cad60f8 100644
--- a/clang/lib/AST/ByteCode/Interp.cpp
+++ b/clang/lib/AST/ByteCode/Interp.cpp
@@ -518,7 +518,7 @@ bool CheckNull(InterpState &S, CodePtr OpPC, const Pointer &Ptr,
 
 bool CheckRange(InterpState &S, CodePtr OpPC, const Pointer &Ptr,
                 AccessKinds AK) {
-  if (!Ptr.isOnePastEnd())
+  if (!Ptr.isOnePastEnd() && !Ptr.isZeroSizeArray())
     return true;
   if (S.getLangOpts().CPlusPlus) {
     const SourceInfo &Loc = S.Current->getSource(OpPC);
@@ -829,8 +829,6 @@ bool CheckFinalLoad(InterpState &S, CodePtr OpPC, const Pointer &Ptr) {
     return false;
   if (!CheckExtern(S, OpPC, Ptr))
     return false;
-  if (!CheckRange(S, OpPC, Ptr, AK_Read))
-    return false;
   if (!CheckActive(S, OpPC, Ptr, AK_Read))
     return false;
   if (!CheckLifetime(S, OpPC, Ptr.getLifetime(), AK_Read))
diff --git a/clang/test/AST/ByteCode/arrays.cpp b/clang/test/AST/ByteCode/arrays.cpp
index 2dd51c2fa6711..087d0e9bd6630 100644
--- a/clang/test/AST/ByteCode/arrays.cpp
+++ b/clang/test/AST/ByteCode/arrays.cpp
@@ -779,3 +779,16 @@ namespace DiscardedSubScriptExpr {
     return true;
   }
 }
+
+namespace ZeroSizeArrayRead {
+  constexpr char str[0] = {};
+  constexpr  unsigned checksum(const char *s) {
+    unsigned result = 0;
+    for (const char *p = s; *p != '\0'; ++p) { // both-note {{read of dereferenced one-past-the-end pointer}}
+      result += *p;
+    }
+    return result;
+  }
+  constexpr unsigned C = checksum(str); // both-error {{must be initialized by a constant expression}} \
+                                        // both-note {{in call to}}
+}