[STLExtras] Add a default value to drop_begin

This patch adds the default value of 1 to drop_begin.

In the llvm codebase, 70% of calls to drop_begin have 1 as the second
argument.  The interface similar to with std::next should improve
readability.

This patch converts a couple of calls to drop_begin as examples.

Differential Revision: https://reviews.llvm.org/D94858

diff --git a/llvm/include/llvm/ADT/STLExtras.h b/llvm/include/llvm/ADT/STLExtras.h
index c8c1aff..63c7f48 100644 (file)
--- a/llvm/include/llvm/ADT/STLExtras.h
+++ b/llvm/include/llvm/ADT/STLExtras.h
@@ -272,7 +272,7 @@ template <typename ContainerTy> bool hasSingleElement(ContainerTy &&C) {
 
 /// Return a range covering \p RangeOrContainer with the first N elements
 /// excluded.
-template <typename T> auto drop_begin(T &&RangeOrContainer, size_t N) {
+template <typename T> auto drop_begin(T &&RangeOrContainer, size_t N = 1) {
   return make_range(std::next(adl_begin(RangeOrContainer), N),
                     adl_end(RangeOrContainer));
 }

diff --git a/llvm/lib/Transforms/Utils/LoopUtils.cpp b/llvm/lib/Transforms/Utils/LoopUtils.cpp
index 401fe45..e6575ee 100644 (file)
--- a/llvm/lib/Transforms/Utils/LoopUtils.cpp
+++ b/llvm/lib/Transforms/Utils/LoopUtils.cpp
@@ -349,7 +349,7 @@ Optional<MDNode *> llvm::makeFollowupLoopID(
 
   bool Changed = false;
   if (InheritAllAttrs || InheritSomeAttrs) {
-    for (const MDOperand &Existing : drop_begin(OrigLoopID->operands(), 1)) {
+    for (const MDOperand &Existing : drop_begin(OrigLoopID->operands())) {
       MDNode *Op = cast<MDNode>(Existing.get());
 
       auto InheritThisAttribute = [InheritSomeAttrs,
@@ -386,7 +386,7 @@ Optional<MDNode *> llvm::makeFollowupLoopID(
       continue;
 
     HasAnyFollowup = true;
-    for (const MDOperand &Option : drop_begin(FollowupNode->operands(), 1)) {
+    for (const MDOperand &Option : drop_begin(FollowupNode->operands())) {
       MDs.push_back(Option.get());
       Changed = true;
     }

diff --git a/llvm/unittests/ADT/STLExtrasTest.cpp b/llvm/unittests/ADT/STLExtrasTest.cpp
index 0196817..8626530 100644 (file)
--- a/llvm/unittests/ADT/STLExtrasTest.cpp
+++ b/llvm/unittests/ADT/STLExtrasTest.cpp
@@ -400,6 +400,17 @@ TEST(STLExtrasTest, DropBeginTest) {
   }
 }
 
+TEST(STLExtrasTest, DropBeginDefaultTest) {
+  SmallVector<int, 5> vec{0, 1, 2, 3, 4};
+
+  int i = 1;
+  for (auto &v : drop_begin(vec)) {
+    EXPECT_EQ(v, i);
+    i += 1;
+  }
+  EXPECT_EQ(i, 5);
+}
+
 TEST(STLExtrasTest, EarlyIncrementTest) {
   std::list<int> L = {1, 2, 3, 4};