From 6b9a706200cbb27e5e863cfd41fb3684ee616e23 Mon Sep 17 00:00:00 2001
From: River Riddle <riddleriver@gmail.com>
Date: Mon, 29 Jun 2020 22:37:05 -0700
Subject: [PATCH] Add front/back accessors to indexed_accessor_range.

These map to the similar accessors on ArrayRef and other random access containers.

This fixes a compilation error on MLIR ODS for variadic operands/results, which relied on the availability of front in certain situations.
---
 llvm/include/llvm/ADT/STLExtras.h     | 8 ++++++++
 mlir/test/lib/Dialect/Test/TestOps.td | 6 ++++++
 2 files changed, 14 insertions(+)

diff --git a/llvm/include/llvm/ADT/STLExtras.h b/llvm/include/llvm/ADT/STLExtras.h
index 1bc4c0c..b2e709f 100644
--- a/llvm/include/llvm/ADT/STLExtras.h
+++ b/llvm/include/llvm/ADT/STLExtras.h
@@ -1121,6 +1121,14 @@ public:
     assert(index < size() && "invalid index for value range");
     return DerivedT::dereference_iterator(base, index);
   }
+  ReferenceT front() const {
+    assert(!empty() && "expected non-empty range");
+    return (*this)[0];
+  }
+  ReferenceT back() const {
+    assert(!empty() && "expected non-empty range");
+    return (*this)[size() - 1];
+  }
 
   /// Compare this range with another.
   template <typename OtherT> bool operator==(const OtherT &other) const {
diff --git a/mlir/test/lib/Dialect/Test/TestOps.td b/mlir/test/lib/Dialect/Test/TestOps.td
index 6aa18c1..bc8f2ff 100644
--- a/mlir/test/lib/Dialect/Test/TestOps.td
+++ b/mlir/test/lib/Dialect/Test/TestOps.td
@@ -124,6 +124,12 @@ def MixedNormalVariadicOperandOp : TEST_Op<
     Variadic<AnyTensor>:$input3
   );
 }
+def VariadicWithSameOperandsResult :
+      TEST_Op<"variadic_with_same_operand_results",
+              [SameOperandsAndResultType]> {
+  let arguments = (ins Variadic<AnySignlessInteger>:$operands);
+  let results = (outs AnySignlessInteger:$result);
+}
 
 //===----------------------------------------------------------------------===//
 // Test Results
-- 
2.7.4