[LLVM] Don't memcpy from a null pointer for empty byte-array properties

[uditagarwal97]

Problem

PropertyValue::PropertyValue(const byte *Data, SizeTy DataBitSize) in llvm/lib/Support/PropertySetIO.cpp ends with:

// Append data.
std::memcpy(Val.ByteArrayVal + SizeFieldSize, Data, DataSize);

Data is null whenever the property value is an empty container: the templated constructor in llvm/include/llvm/Support/PropertySetIO.h forwards Data.data(), and for an empty std::vector<char>/SmallVector that is nullptr. memcpy's parameters are declared __attribute__((nonnull)), so memcpy(dst, nullptr, 0) is undefined behaviour even though the length is zero (https://en.cppreference.com/cpp/string/byte/memcpy)

UBSan diagnostic (build configured with -DLLVM_USE_SANITIZER=Address;Undefined):

llvm/lib/Support/PropertySetIO.cpp:171:49: runtime error: null pointer passed as
argument 2, which is declared to never be null
/usr/include/string.h:44:28: note: nonnull attribute specified here
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior

Fix

Skip the copy when there is nothing to copy:

// Append data. Data may be null when DataSize is zero, and memcpy declares
// its source as nonnull, so guard the call.
if (DataSize > 0)
  std::memcpy(Val.ByteArrayVal + SizeFieldSize, Data, DataSize);

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Co-Authored-By: Claude Opus 5 (1M context) noreply@anthropic.com

[Copilot]

🟢 Approval recommended

The focused fix correctly addresses the undefined behavior and includes suitable regression coverage.

Pull request overview

Prevents undefined behavior when constructing empty byte-array properties.

Changes:

• Guards memcpy when the data size is zero.
• Adds a regression test for empty containers.

File summaries

File	Description
llvm/lib/Support/PropertySetIO.cpp	Skips zero-length byte-array copies.
llvm/unittests/Support/PropertySetIOTest.cpp	Tests empty byte-array construction.

Review details

• Files reviewed: 2/2 changed files
• Comments generated: 0
• Review effort level: Balanced

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[YuriPlyakhin]

LGTM

[uditagarwal97]

CI failure is unrelated. Merging!

  Timed Out Tests (1):
    SYCL :: Basic/accessor/accessor.cpp