[PATCH] D52236: [ADT][BitVector] Add push_back()

[Simon Pilgrim via Phabricator via llvm-commits]

RKSimon created this revision.
RKSimon added reviewers: zturner, efriedma, craig.topper, spatel.
Herald added a subscriber: dexonsmith.

Add a higher performance alternative to calling resize() every time which performs a lot of clearing to zero - when we're adding a single bit most of the time this will be completely unnecessary.

Converting CodeGenDAGPatterns::GenerateVariants() to use this saves 10secs in debug builds of x86 -gen-dag-isel


Repository:
  rL LLVM

https://reviews.llvm.org/D52236

Files:
  include/llvm/ADT/BitVector.h
  include/llvm/ADT/SmallBitVector.h
  unittests/ADT/BitVectorTest.cpp


Index: unittests/ADT/BitVectorTest.cpp
===================================================================
--- unittests/ADT/BitVectorTest.cpp
+++ unittests/ADT/BitVectorTest.cpp
@@ -836,5 +836,27 @@
   for (unsigned Bit : ToFill.set_bits())
     EXPECT_EQ(List[i++], Bit);
 }
+
+TYPED_TEST(BitVectorTest, PushBack) {
+  TypeParam Vec(10, false);
+  Vec.push_back(true);
+  EXPECT_EQ(10, Vec.find_first());
+  EXPECT_EQ(10, Vec.find_last());
+
+  Vec.push_back(false);
+  EXPECT_EQ(10, Vec.find_first());
+  EXPECT_EQ(10, Vec.find_last());
+
+  Vec.push_back(true);
+  EXPECT_EQ(10, Vec.find_first());
+  EXPECT_EQ(12, Vec.find_last());
+
+  // Add a lot of values to cause reallocation.
+  for (int i = 0; i != 100; ++i) {
+    Vec.push_back(true);
+    Vec.push_back(false);
+  }
+  EXPECT_EQ(102, Vec.count());
+}
 }
 #endif
Index: include/llvm/ADT/SmallBitVector.h
===================================================================
--- include/llvm/ADT/SmallBitVector.h
+++ include/llvm/ADT/SmallBitVector.h
@@ -465,6 +465,11 @@
     return (*this)[Idx];
   }
 
+  // Push single bit to end of vector.
+  void push_back(bool Val) {
+    resize(size() + 1, Val);
+  }
+
   /// Test if any common bits are set.
   bool anyCommon(const SmallBitVector &RHS) const {
     if (isSmall() && RHS.isSmall())
Index: include/llvm/ADT/BitVector.h
===================================================================
--- include/llvm/ADT/BitVector.h
+++ include/llvm/ADT/BitVector.h
@@ -503,6 +503,23 @@
     return (*this)[Idx];
   }
 
+  // Push single bit to end of vector.
+  void push_back(bool Val) {
+    unsigned OldSize = Size;
+    unsigned NewSize = Size + 1;
+
+    // Resize, which will insert zeros.
+    // If we already fit then the unused bits will be already zero.
+    if (NewSize > getBitCapacity())
+      resize(NewSize, false);
+    else
+      Size = NewSize;
+
+    // If true, set single bit.
+    if (Val)
+      set(OldSize);
+  }
+
   /// Test if any common bits are set.
   bool anyCommon(const BitVector &RHS) const {
     unsigned ThisWords = NumBitWords(size());


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