IR: Add Value::sortUseList()

Add `Value::sortUseList()`, templated on the comparison function to use.

The sort is an iterative merge sort that uses a binomial vector of
already-merged lists to limit the size overhead to `O(1)`.

This is part of PR5680.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@213824 91177308-0d34-0410-b5e6-96231b3b80d8

unittests/IR/UseTest.cpp

@@ -0,0 +1,62 @@
+//===- llvm/unittest/IR/UseTest.cpp - Use unit tests ----------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/AsmParser/Parser.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/LLVMContext.h"
+#include "llvm/IR/Module.h"
+#include "llvm/IR/User.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/Support/SourceMgr.h"
+#include "gtest/gtest.h"
+using namespace llvm;
+
+namespace {
+
+TEST(UseTest, sort) {
+  LLVMContext C;
+
+  const char *ModuleString = "define void @f(i32 %x) {\n"
+                             "entry:\n"
+                             "  %v0 = add i32 %x, 0\n"
+                             "  %v2 = add i32 %x, 2\n"
+                             "  %v5 = add i32 %x, 5\n"
+                             "  %v1 = add i32 %x, 1\n"
+                             "  %v3 = add i32 %x, 3\n"
+                             "  %v7 = add i32 %x, 7\n"
+                             "  %v6 = add i32 %x, 6\n"
+                             "  %v4 = add i32 %x, 4\n"
+                             "  ret void\n"
+                             "}\n";
+  SMDiagnostic Err;
+  Module *M = ParseAssemblyString(ModuleString, nullptr, Err, C);
+  Function *F = M->getFunction("f");
+  ASSERT_TRUE(F);
+  ASSERT_TRUE(F->arg_begin() != F->arg_end());
+  Argument &X = *F->arg_begin();
+  ASSERT_EQ("x", X.getName());
+
+  X.sortUseList([](const Use &L, const Use &R) {
+    return L.getUser()->getName() < R.getUser()->getName();
+  });
+  unsigned I = 0;
+  for (User *U : X.users())
+    EXPECT_EQ("v" + std::to_string(I++), U->getName());
+  ASSERT_EQ(8u, I);
+
+  X.sortUseList([](const Use &L, const Use &R) {
+    return L.getUser()->getName() > R.getUser()->getName();
+  });
+  I = 0;
+  for (User *U : X.users())
+    EXPECT_EQ("v" + std::to_string((7 - I++)), U->getName());
+  ASSERT_EQ(8u, I);
+}
+
+} // end anonymous namespace