From c9e52fbe4d4fa37a87b2855ad7e118dcdee2db68 Mon Sep 17 00:00:00 2001
From: Jakub Kuderski <kubak@google.com>
Date: Mon, 22 Aug 2022 23:55:05 -0400
Subject: [PATCH] [ADT] Add all_equal predicate

`llvm::all_equal` checks if all values in the given range are equal, i.e., there are no two elements that are not equal.
Similar to `llvm::all_of`, it returns `true` when the range is empty.

`llvm::all_equal` is intended to supersede `llvm::is_splat`, which will be deprecated and removed in future patches.
See the discussion thread for more details:
https://discourse.llvm.org/t/adt-is-splat-and-empty-ranges/64692.

Reviewed By: dblaikie, shchenz

Differential Revision: https://reviews.llvm.org/D132334
---
 llvm/include/llvm/ADT/STLExtras.h    | 25 +++++++++++++++++--------
 llvm/unittests/ADT/STLExtrasTest.cpp | 23 +++++++++++++++++++++++
 2 files changed, 40 insertions(+), 8 deletions(-)

diff --git a/llvm/include/llvm/ADT/STLExtras.h b/llvm/include/llvm/ADT/STLExtras.h
index 9173719..44f86e4 100644
--- a/llvm/include/llvm/ADT/STLExtras.h
+++ b/llvm/include/llvm/ADT/STLExtras.h
@@ -1763,16 +1763,25 @@ template <typename L, typename R> bool equal(L &&LRange, R &&RRange) {
                     adl_end(RRange));
 }
 
-/// Wrapper function around std::equal to detect if all elements
-/// in a container are same.
-template <typename R>
-bool is_splat(R &&Range) {
-  size_t range_size = size(Range);
-  return range_size != 0 && (range_size == 1 ||
-         std::equal(adl_begin(Range) + 1, adl_end(Range), adl_begin(Range)));
+/// Returns true if all elements in Range are equal or when the Range is empty.
+template <typename R> bool all_equal(R &&Range) {
+  auto Begin = adl_begin(Range);
+  auto End = adl_end(Range);
+  return Begin == End || std::equal(Begin + 1, End, Begin);
+}
+
+/// Returns true if all Values in the initializer lists are equal or the list
+// is empty.
+template <typename T> bool all_equal(std::initializer_list<T> Values) {
+  return all_equal<std::initializer_list<T>>(std::move(Values));
+}
+
+/// Returns true if Range consists of the same value repeated multiple times.
+template <typename R> bool is_splat(R &&Range) {
+  return !llvm::empty(Range) && all_equal(Range);
 }
 
-/// Returns true iff all Values in the initializer lists are same.
+/// Returns true if Values consists of the same value repeated multiple times.
 template <typename T> bool is_splat(std::initializer_list<T> Values) {
   return is_splat<std::initializer_list<T>>(std::move(Values));
 }
diff --git a/llvm/unittests/ADT/STLExtrasTest.cpp b/llvm/unittests/ADT/STLExtrasTest.cpp
index 8ae5020..9b0af51 100644
--- a/llvm/unittests/ADT/STLExtrasTest.cpp
+++ b/llvm/unittests/ADT/STLExtrasTest.cpp
@@ -588,6 +588,29 @@ TEST(STLExtrasTest, EarlyIncrementTestCustomPointerIterator) {
   EXPECT_EQ(EIR.end(), I);
 }
 
+TEST(STLExtrasTest, AllEqual) {
+  std::vector<int> V;
+  EXPECT_TRUE(all_equal(V));
+
+  V.push_back(1);
+  EXPECT_TRUE(all_equal(V));
+
+  V.push_back(1);
+  V.push_back(1);
+  EXPECT_TRUE(all_equal(V));
+
+  V.push_back(2);
+  EXPECT_FALSE(all_equal(V));
+}
+
+TEST(STLExtrasTest, AllEqualInitializerList) {
+  EXPECT_TRUE(all_equal({1}));
+  EXPECT_TRUE(all_equal({1, 1}));
+  EXPECT_FALSE(all_equal({1, 2}));
+  EXPECT_FALSE(all_equal({2, 1}));
+  EXPECT_TRUE(all_equal({1, 1, 1}));
+}
+
 TEST(STLExtrasTest, IsSplat) {
   std::vector<int> V;
   EXPECT_FALSE(is_splat(V));
-- 
2.7.4