[CodeMoverUtils] Added an API to check if an instruction can be safely

moved before another instruction.
Summary:Added an API to check if an instruction can be safely moved
before another instruction. In future PRs, we will like to add support
of moving instructions between blocks that are not control flow
equivalent, and add other APIs to enhance usability, e.g. moving basic
blocks, moving list of instructions...
Loop Fusion will be its first user. When there is intervening code in
between two loops, fusion is currently unable to fuse them. Loop Fusion
can use this utility to check if the intervening code can be safely
moved before or after the two loops, and move them, then it can
successfully fuse them.
Reviewer:kbarton,jdoerfert,Meinersbur,bmahjour,etiotto
Reviewed By:bmahjour
Subscribers:mgorny,hiraditya,llvm-commits
Tag:LLVM
Differential Revision:https://reviews.llvm.org/D70049

2 files changed, 173 insertions, 0 deletions

diff --git a/llvm/unittests/Transforms/Utils/CMakeLists.txt b/llvm/unittests/Transforms/Utils/CMakeLists.txt
index 8d9d7df4f40..5a8204cb86a 100644
--- a/llvm/unittests/Transforms/Utils/CMakeLists.txt
+++ b/llvm/unittests/Transforms/Utils/CMakeLists.txt
@@ -11,6 +11,7 @@ add_llvm_unittest(UtilsTests
   BasicBlockUtilsTest.cpp
   CloningTest.cpp
   CodeExtractorTest.cpp
+  CodeMoverUtilsTest.cpp
   FunctionComparatorTest.cpp
   IntegerDivisionTest.cpp
   LocalTest.cpp
diff --git a/llvm/unittests/Transforms/Utils/CodeMoverUtilsTest.cpp b/llvm/unittests/Transforms/Utils/CodeMoverUtilsTest.cpp
new file mode 100644
index 00000000000..64c4f796cb8
--- /dev/null
+++ b/llvm/unittests/Transforms/Utils/CodeMoverUtilsTest.cpp
@@ -0,0 +1,172 @@
+//===- CodeMoverUtils.cpp - Unit tests for CodeMoverUtils ---------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Transforms/Utils/CodeMoverUtils.h"
+#include "llvm/Analysis/AssumptionCache.h"
+#include "llvm/Analysis/DependenceAnalysis.h"
+#include "llvm/Analysis/LoopInfo.h"
+#include "llvm/Analysis/PostDominators.h"
+#include "llvm/Analysis/ScalarEvolutionExpander.h"
+#include "llvm/AsmParser/Parser.h"
+#include "llvm/IR/Dominators.h"
+#include "llvm/IR/LLVMContext.h"
+#include "llvm/Support/SourceMgr.h"
+#include "gtest/gtest.h"
+
+using namespace llvm;
+
+static std::unique_ptr<Module> parseIR(LLVMContext &C, const char *IR) {
+  SMDiagnostic Err;
+  std::unique_ptr<Module> Mod = parseAssemblyString(IR, Err, C);
+  if (!Mod)
+    Err.print("CodeMoverUtilsTests", errs());
+  return Mod;
+}
+
+static void run(Module &M, StringRef FuncName,
+                function_ref<void(Function &F, DominatorTree &DT,
+                                  PostDominatorTree &PDT, DependenceInfo &DI)>
+                    Test) {
+  auto *F = M.getFunction(FuncName);
+  DominatorTree DT(*F);
+  PostDominatorTree PDT(*F);
+  TargetLibraryInfoImpl TLII;
+  TargetLibraryInfo TLI(TLII);
+  AssumptionCache AC(*F);
+  AliasAnalysis AA(TLI);
+  LoopInfo LI(DT);
+  ScalarEvolution SE(*F, TLI, AC, DT, LI);
+  DependenceInfo DI(F, &AA, &SE, &LI);
+  Test(*F, DT, PDT, DI);
+}
+
+TEST(CodeMoverUtils, BasicTest) {
+  LLVMContext C;
+
+  // void safecall() noexcept willreturn nosync;
+  // void unsafecall();
+  // void foo(int * __restrict__ A, int * __restrict__ B, int * __restrict__ C,
+  //          long N) {
+  //   X = N / 1;
+  //   safecall();
+  //   unsafecall1();
+  //   unsafecall2();
+  //   for (long i = 0; i < N; ++i) {
+  //     A[5] = 5;
+  //     A[i] = 0;
+  //     B[i] = A[i];
+  //     C[i] = A[i];
+  //     A[6] = 6;
+  //   }
+  // }
+  std::unique_ptr<Module> M = parseIR(
+      C,
+      "define void @foo(i32* noalias %A, i32* noalias %B, i32* noalias %C\n"
+      "                  , i64 %N) {\n"
+      "entry:\n"
+      "  %X = sdiv i64 1, %N\n"
+      "  call void @safecall()\n"
+      "  %cmp1 = icmp slt i64 0, %N\n"
+      "  call void @unsafecall1()\n"
+      "  call void @unsafecall2()\n"
+      "  br i1 %cmp1, label %for.body, label %for.end\n"
+      "for.body:\n"
+      "  %i = phi i64 [ 0, %entry ], [ %inc, %for.body ]\n"
+      "  %arrayidx_A5 = getelementptr inbounds i32, i32* %A, i64 5\n"
+      "  store i32 5, i32* %arrayidx_A5, align 4\n"
+      "  %arrayidx_A = getelementptr inbounds i32, i32* %A, i64 %i\n"
+      "  store i32 0, i32* %arrayidx_A, align 4\n"
+      "  %load1 = load i32, i32* %arrayidx_A, align 4\n"
+      "  %arrayidx_B = getelementptr inbounds i32, i32* %B, i64 %i\n"
+      "  store i32 %load1, i32* %arrayidx_B, align 4\n"
+      "  %load2 = load i32, i32* %arrayidx_A, align 4\n"
+      "  %arrayidx_C = getelementptr inbounds i32, i32* %C, i64 %i\n"
+      "  store i32 %load2, i32* %arrayidx_C, align 4\n"
+      "  %arrayidx_A6 = getelementptr inbounds i32, i32* %A, i64 6\n"
+      "  store i32 6, i32* %arrayidx_A6, align 4\n"
+      "  %inc = add nsw i64 %i, 1\n"
+      "  %cmp = icmp slt i64 %inc, %N\n"
+      "  br i1 %cmp, label %for.body, label %for.end\n"
+      "for.end:\n"
+      "  ret void\n"
+      "}\n"
+      "declare void @safecall() nounwind nosync willreturn\n"
+      "declare void @unsafecall1()\n"
+      "declare void @unsafecall2()\n");
+
+  run(*M, "foo",
+      [&](Function &F, DominatorTree &DT, PostDominatorTree &PDT,
+          DependenceInfo &DI) {
+        Function::iterator FI = F.begin();
+        BasicBlock *Entry = &*(FI++);
+        assert(Entry->getName() == "entry" && "Expecting BasicBlock entry");
+        Instruction *CI_safecall = Entry->front().getNextNode();
+        assert(isa<CallInst>(CI_safecall) && "Expecting CI_safecall to be a CallInst");
+        Instruction *CI_unsafecall = CI_safecall->getNextNode()->getNextNode();
+        assert(isa<CallInst>(CI_unsafecall) && "Expecting CI_unsafecall to be a CallInst");
+        BasicBlock *ForBody = &*(FI++);
+        assert(ForBody->getName() == "for.body" &&
+               "Expecting BasicBlock for.body");
+        Instruction &PN = ForBody->front();
+        assert(isa<PHINode>(PN) && "Expecting PN to be a PHINode");
+        Instruction *SI_A5 = PN.getNextNode()->getNextNode();
+        assert(isa<StoreInst>(SI_A5) &&
+               SI_A5->getOperand(1)->getName() == "arrayidx_A5" &&
+               "Expecting store to arrayidx_A5");
+        Instruction *SI = SI_A5->getNextNode()->getNextNode();
+        assert(isa<StoreInst>(SI) &&
+               SI->getOperand(1)->getName() == "arrayidx_A" &&
+               "Expecting store to arrayidx_A");
+        Instruction *LI1 = SI->getNextNode();
+        assert(LI1->getName() == "load1" && "Expecting LI1 to be load1");
+        Instruction *LI2 = LI1->getNextNode()->getNextNode()->getNextNode();
+        assert(LI2->getName() == "load2" && "Expecting LI2 to be load2");
+        Instruction *SI_A6 = LI2->getNextNode()->getNextNode()->getNextNode()->getNextNode();
+        assert(isa<StoreInst>(SI_A6) &&
+               SI_A6->getOperand(1)->getName() == "arrayidx_A6" &&
+               "Expecting store to arrayidx_A6");
+
+        // Can move after CI_safecall, as it does not throw, not synchronize, or must return.
+        EXPECT_TRUE(isSafeToMoveBefore(*CI_safecall->getPrevNode(), *CI_safecall->getNextNode(), DT, PDT, DI));
+
+        // Cannot move CI_unsafecall, as it may throw.
+        EXPECT_FALSE(isSafeToMoveBefore(*CI_unsafecall->getNextNode(), *CI_unsafecall, DT, PDT, DI));
+
+        // Moving instruction to non control flow equivalent places are not
+        // supported.
+        EXPECT_FALSE(isSafeToMoveBefore(*SI_A5, *Entry->getTerminator(), DT, PDT, DI));
+
+        // Moving PHINode is not supported.
+        EXPECT_FALSE(isSafeToMoveBefore(PN, *PN.getPrevNode(), DT, PDT, DI));
+
+        // Cannot move non-PHINode before PHINode.
+        EXPECT_FALSE(isSafeToMoveBefore(*PN.getNextNode(), PN, DT, PDT, DI));
+
+        // Moving Terminator is not supported.
+        EXPECT_FALSE(isSafeToMoveBefore(*Entry->getTerminator(), *PN.getNextNode(), DT,
+                                PDT, DI));
+
+        // Cannot move %arrayidx_A after SI, as SI is its user.
+        EXPECT_FALSE(isSafeToMoveBefore(*SI->getPrevNode(), *SI->getNextNode(), DT, PDT, DI));
+
+        // Cannot move SI before %arrayidx_A, as %arrayidx_A is its operand.
+        EXPECT_FALSE(isSafeToMoveBefore(*SI, *SI->getPrevNode(), DT, PDT, DI));
+
+        // Cannot move LI2 after SI_A6, as there is a flow dependence.
+        EXPECT_FALSE(isSafeToMoveBefore(*LI2, *SI_A6->getNextNode(), DT, PDT, DI));
+
+        // Cannot move SI after LI1, as there is a anti dependence.
+        EXPECT_FALSE(isSafeToMoveBefore(*SI, *LI1->getNextNode(), DT, PDT, DI));
+
+        // Cannot move SI_A5 after SI, as there is a output dependence.
+        EXPECT_FALSE(isSafeToMoveBefore(*SI_A5, *LI1, DT, PDT, DI));
+
+        // Can move LI2 before LI1, as there is only an input dependence.
+        EXPECT_TRUE(isSafeToMoveBefore(*LI2, *LI1, DT, PDT, DI));
+      });
+}