[clang] [clang][bytecode] Fix emitting dtors of zero-sized arrays (PR #134672)

[Timm Baeder via cfe-commits]

https://github.com/tbaederr created 
https://github.com/llvm/llvm-project/pull/134672

Desc->getNumElems() returning 0 made us underflow here.

>From 276b187e1d988b26d357052cce239e7eccd0cb4f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Timm=20B=C3=A4der?= <tbae...@redhat.com>
Date: Mon, 7 Apr 2025 17:25:06 +0200
Subject: [PATCH] [clang][bytecode] Fix emitting dtors of zero-sized arrays

Desc->getNumElems() returning 0 made us underflow here.
---
 clang/lib/AST/ByteCode/Compiler.cpp | 20 +++++++++++---------
 clang/test/AST/ByteCode/cxx23.cpp   | 12 ++++++++++++
 2 files changed, 23 insertions(+), 9 deletions(-)

diff --git a/clang/lib/AST/ByteCode/Compiler.cpp 
b/clang/lib/AST/ByteCode/Compiler.cpp
index 021acbd798646..9e9252558b1a9 100644
--- a/clang/lib/AST/ByteCode/Compiler.cpp
+++ b/clang/lib/AST/ByteCode/Compiler.cpp
@@ -6818,15 +6818,17 @@ bool Compiler<Emitter>::emitDestruction(const 
Descriptor *Desc,
         return true;
     }
 
-    for (ssize_t I = Desc->getNumElems() - 1; I >= 0; --I) {
-      if (!this->emitConstUint64(I, Loc))
-        return false;
-      if (!this->emitArrayElemPtrUint64(Loc))
-        return false;
-      if (!this->emitDestruction(ElemDesc, Loc))
-        return false;
-      if (!this->emitPopPtr(Loc))
-        return false;
+    if (size_t N = Desc->getNumElems()) {
+      for (ssize_t I = N - 1; I >= 0; --I) {
+        if (!this->emitConstUint64(I, Loc))
+          return false;
+        if (!this->emitArrayElemPtrUint64(Loc))
+          return false;
+        if (!this->emitDestruction(ElemDesc, Loc))
+          return false;
+        if (!this->emitPopPtr(Loc))
+          return false;
+      }
     }
     return true;
   }
diff --git a/clang/test/AST/ByteCode/cxx23.cpp 
b/clang/test/AST/ByteCode/cxx23.cpp
index 6a62ac11cde79..d0ade4f5278b1 100644
--- a/clang/test/AST/ByteCode/cxx23.cpp
+++ b/clang/test/AST/ByteCode/cxx23.cpp
@@ -304,3 +304,15 @@ namespace NonLiteralDtorInParam {
                               // expected23-note {{non-constexpr function 
'~NonLiteral' cannot be used in a constant expression}}
   }
 }
+
+namespace ZeroSizedArray {
+  struct S {
+    constexpr ~S() {
+    }
+  };
+  constexpr int foo() {
+    S s[0];
+    return 1;
+  }
+  static_assert(foo() == 1);
+}

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