[llvm] [ADT] Add `from_range` constructor for (Small)DenseMap (PR #153515)

[Jakub Kuderski via llvm-commits]

https://github.com/kuhar created https://github.com/llvm/llvm-project/pull/153515

This follows how we support range construction for (Small)DenseSet.

>From 6bf0cb8a8ca66c355e3c33f4ea5d2f9a530a32a8 Mon Sep 17 00:00:00 2001
From: Jakub Kuderski <jakub at nod-labs.com>
Date: Wed, 13 Aug 2025 20:49:41 -0400
Subject: [PATCH] [ADT] Add `from_range` constructor for (Small)DenseMap

This follows how we support (Small)DenseSet.
---
 llvm/include/llvm/ADT/DenseMap.h    | 15 +++++++++++----
 llvm/unittests/ADT/DenseMapTest.cpp | 29 +++++++++++++++++++++++++++++
 2 files changed, 40 insertions(+), 4 deletions(-)

diff --git a/llvm/include/llvm/ADT/DenseMap.h b/llvm/include/llvm/ADT/DenseMap.h
index 1f2721322e34a..2a35c3d583f70 100644
--- a/llvm/include/llvm/ADT/DenseMap.h
+++ b/llvm/include/llvm/ADT/DenseMap.h
@@ -18,6 +18,7 @@
 #include "llvm/ADT/DenseMapInfo.h"
 #include "llvm/ADT/EpochTracker.h"
 #include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/STLForwardCompat.h"
 #include "llvm/Support/AlignOf.h"
 #include "llvm/Support/Compiler.h"
 #include "llvm/Support/MathExtras.h"
@@ -811,10 +812,12 @@ class DenseMap : public DenseMapBase<DenseMap<KeyT, ValueT, KeyInfoT, BucketT>,
     this->insert(I, E);
   }
 
-  DenseMap(std::initializer_list<typename BaseT::value_type> Vals) {
-    init(Vals.size());
-    this->insert(Vals.begin(), Vals.end());
-  }
+  template <typename RangeT>
+  DenseMap(llvm::from_range_t, const RangeT &Range)
+      : DenseMap(adl_begin(Range), adl_end(Range)) {}
+
+  DenseMap(std::initializer_list<typename BaseT::value_type> Vals)
+      : DenseMap(Vals.begin(), Vals.end()) {}
 
   ~DenseMap() {
     this->destroyAll();
@@ -985,6 +988,10 @@ class SmallDenseMap
     this->insert(I, E);
   }
 
+  template <typename RangeT>
+  SmallDenseMap(llvm::from_range_t, const RangeT &Range)
+      : SmallDenseMap(adl_begin(Range), adl_end(Range)) {}
+
   SmallDenseMap(std::initializer_list<typename BaseT::value_type> Vals)
       : SmallDenseMap(Vals.begin(), Vals.end()) {}
 
diff --git a/llvm/unittests/ADT/DenseMapTest.cpp b/llvm/unittests/ADT/DenseMapTest.cpp
index bdfbc8557859a..fdecfb7bb5b0b 100644
--- a/llvm/unittests/ADT/DenseMapTest.cpp
+++ b/llvm/unittests/ADT/DenseMapTest.cpp
@@ -10,6 +10,7 @@
 #include "CountCopyAndMove.h"
 #include "llvm/ADT/DenseMapInfo.h"
 #include "llvm/ADT/DenseMapInfoVariant.h"
+#include "llvm/ADT/STLForwardCompat.h"
 #include "llvm/ADT/SmallSet.h"
 #include "llvm/ADT/StringRef.h"
 #include "gmock/gmock.h"
@@ -249,6 +250,25 @@ TYPED_TEST(DenseMapTest, CopyConstructorNotSmallTest) {
     EXPECT_EQ(this->getValue(Key), copyMap[this->getKey(Key)]);
 }
 
+// Test range constructors.
+TYPED_TEST(DenseMapTest, RangeConstructorTest) {
+  using KeyAndValue =
+      std::pair<typename TypeParam::key_type, typename TypeParam::mapped_type>;
+  KeyAndValue PlainArray[] = {{this->getKey(0), this->getValue(0)},
+                              {this->getKey(1), this->getValue(1)}};
+
+  TypeParam MapFromRange(llvm::from_range, PlainArray);
+  EXPECT_EQ(2u, MapFromRange.size());
+  EXPECT_EQ(this->getValue(0), MapFromRange[this->getKey(0)]);
+  EXPECT_EQ(this->getValue(1), MapFromRange[this->getKey(1)]);
+
+  TypeParam MapFromInitList({{this->getKey(0), this->getValue(1)},
+                             {this->getKey(1), this->getValue(2)}});
+  EXPECT_EQ(2u, MapFromInitList.size());
+  EXPECT_EQ(this->getValue(1), MapFromInitList[this->getKey(0)]);
+  EXPECT_EQ(this->getValue(2), MapFromInitList[this->getKey(1)]);
+}
+
 // Test copying from a default-constructed map.
 TYPED_TEST(DenseMapTest, CopyConstructorFromDefaultTest) {
   TypeParam copyMap(this->Map);
@@ -726,6 +746,15 @@ TEST(DenseMapCustomTest, FindAsTest) {
   EXPECT_TRUE(map.find_as("d") == map.end());
 }
 
+TEST(DenseMapCustomTest, SmallDenseMapFromRange) {
+  std::pair<int, StringRef> PlainArray[] = {{0, "0"}, {1, "1"}, {2, "2"}};
+  SmallDenseMap<int, StringRef> M(llvm::from_range, PlainArray);
+  EXPECT_EQ(3u, M.size());
+  using testing::Pair;
+  EXPECT_THAT(M, testing::UnorderedElementsAre(Pair(0, "0"), Pair(1, "1"),
+                                               Pair(2, "2")));
+}
+
 TEST(DenseMapCustomTest, SmallDenseMapInitializerList) {
   SmallDenseMap<int, int> M = {{0, 0}, {0, 1}, {1, 2}};
   EXPECT_EQ(2u, M.size());