[Mlir-commits] [mlir] [mlir] Fix alignment assertion for empty DenseArrayAttr (PR #211730)

[Vitaly Buka]

https://github.com/vitalybuka created https://github.com/llvm/llvm-project/pull/211730

After #207274, libc++ fails __assume_aligned assertion in __assume_valid_range.

`operator ArrayRef<T>()` just a cast of
`raw.data()`. `raw` is aligned copy of range from
from BytecodeReader done by
Builtin_DenseArrayRawDataParameter allocator.
However, if range is empty, aligned copying was
omitted, leaving unaligned `ArrayRef<char>`.

The fix is to replace unalined ArrayRef<> with
aligned default constructed.


>From 6fa48ea848628ed240e3e1ecdda5aa9039f4491e Mon Sep 17 00:00:00 2001
From: Vitaly Buka <vitalybuka at google.com>
Date: Thu, 23 Jul 2026 22:52:53 -0700
Subject: [PATCH] =?UTF-8?q?[=F0=9D=98=80=F0=9D=97=BD=F0=9D=97=BF]=20initia?=
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Created using spr 1.3.7
---
 mlir/include/mlir/IR/BuiltinAttributes.td | 3 +++
 mlir/lib/IR/BuiltinAttributes.cpp         | 2 ++
 2 files changed, 5 insertions(+)

diff --git a/mlir/include/mlir/IR/BuiltinAttributes.td b/mlir/include/mlir/IR/BuiltinAttributes.td
index f238137734d56..ba2c374a9ab48 100644
--- a/mlir/include/mlir/IR/BuiltinAttributes.td
+++ b/mlir/include/mlir/IR/BuiltinAttributes.td
@@ -160,6 +160,9 @@ def Builtin_DenseArrayRawDataParameter : ArrayRefParameter<
           $_allocator.allocate($_self.size(), alignof(uint64_t)));
       llvm::uninitialized_copy($_self, alloc);
       $_dst = ArrayRef<char>(alloc, $_self.size());
+    } else {
+      // Align possibly unaligned empty range.
+      $_dst = {};
     }
   }];
 }
diff --git a/mlir/lib/IR/BuiltinAttributes.cpp b/mlir/lib/IR/BuiltinAttributes.cpp
index 9fda2ef8e5059..888b989785498 100644
--- a/mlir/lib/IR/BuiltinAttributes.cpp
+++ b/mlir/lib/IR/BuiltinAttributes.cpp
@@ -21,6 +21,7 @@
 #include "llvm/ADT/APSInt.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/DebugLog.h"
+#include "llvm/Support/Alignment.h"
 #include "llvm/Support/Endian.h"
 #include <optional>
 
@@ -822,6 +823,7 @@ Attribute DenseArrayAttrImpl<T>::parse(AsmParser &parser, Type odsType) {
 template <typename T>
 DenseArrayAttrImpl<T>::operator ArrayRef<T>() const {
   ArrayRef<char> raw = getRawData();
+  assert(llvm::isAddrAligned(llvm::Align(alignof(T)), raw.data()));
   assert((raw.size() % sizeof(T)) == 0);
   return ArrayRef<T>(reinterpret_cast<const T *>(raw.data()),
                      raw.size() / sizeof(T));