Save the induction binary operator in IVDescriptors for non FP induction variables.

[Whitney]

Summary

Currently InductionBinOps are only saved for FP induction variables, the PR extends it with non FP induction variable, so user of IVDescriptors can query the InductionBinOps for integer induction variables.

The changes in hasUnsafeAlgebra() and getUnsafeAlgebraInst() are required for the existing LIT test cases to pass. As described in the comment of the two functions, one of the requirement to return true is it is a FP induction variable. The checks was not needed because InductionBinOp was not set on non FP cases before.

https://reviews.llvm.org/D60565 depends on the patch.

[Whitney]

clang-format

[Whitney]

Any comments?

[jdoerfert]

LGTM

llvm/include/llvm/Analysis/IVDescriptors.h

public:
   static bool isInductionPHI(PHINode *Phi, const Loop *L,
                              PredicatedScalarEvolution &PSE,
                              InductionDescriptor &D, bool Assume = false);
 
   /// Returns true if the induction type is FP and the binary operator does
   /// not have the "fast-math" property. Such operation requires a relaxed FP
   /// mode.
   bool hasUnsafeAlgebra() {
-    return InductionBinOp && !cast<FPMathOperator>(InductionBinOp)->isFast();
+    return IK == IK_FpInduction && InductionBinOp &&
+           !cast<FPMathOperator>(InductionBinOp)->isFast();
   }
 
   /// Returns induction operator that does not have "fast-math" property
   /// and requires FP unsafe mode.
   Instruction *getUnsafeAlgebraInst() {
+    if (IK != IK_FpInduction)
+      return nullptr;
+
     if (!InductionBinOp || cast<FPMathOperator>(InductionBinOp)->isFast())
       return nullptr;
     return InductionBinOp;
   }
 
   /// Returns binary opcode of the induction operator.
   Instruction::BinaryOps getInductionOpcode() const {
     return InductionBinOp ? InductionBinOp->getOpcode()

llvm/lib/Analysis/IVDescriptors.cpp

if (AR->getLoop() != TheLoop) {
     // don't currently know how to handled uniform PHIs.
     LLVM_DEBUG(
         dbgs() << "LV: PHI is a recurrence with respect to an outer loop.\n");
     return false;
   }
 
   Value *StartValue =
       Phi->getIncomingValueForBlock(AR->getLoop()->getLoopPreheader());
+
+  BasicBlock *Latch = AR->getLoop()->getLoopLatch();
+  if (!Latch)
+    return false;
+  BinaryOperator *BOp =
+      dyn_cast<BinaryOperator>(Phi->getIncomingValueForBlock(Latch));
+
   const SCEV *Step = AR->getStepRecurrence(*SE);
   // Calculate the pointer stride and check if it is consecutive.
   // The stride may be a constant or a loop invariant integer value.
   const SCEVConstant *ConstStep = dyn_cast<SCEVConstant>(Step);
   if (!ConstStep && !SE->isLoopInvariant(Step, TheLoop))
     return false;
 
   if (PhiTy->isIntegerTy()) {
-    D = InductionDescriptor(StartValue, IK_IntInduction, Step, /*BOp=*/nullptr,
+    D = InductionDescriptor(StartValue, IK_IntInduction, Step, BOp,
                             CastsToIgnore);
     return true;
   }
 
   assert(PhiTy->isPointerTy() && "The PHI must be a pointer");
   // Pointer induction should be a constant.
   if (!ConstStep)
     return false;
bool InductionDescriptor::isInductionPHI(
   if (!Size)
     return false;
 
   int64_t CVSize = CV->getSExtValue();
   if (CVSize % Size)
     return false;
   auto *StepValue =
       SE->getConstant(CV->getType(), CVSize / Size, true /* signed */);
-  D = InductionDescriptor(StartValue, IK_PtrInduction, StepValue);
+  D = InductionDescriptor(StartValue, IK_PtrInduction, StepValue, BOp);
   return true;
 }

llvm/unittests/Analysis/CMakeLists.txt

add_llvm_unittest(AnalysisTests
   BranchProbabilityInfoTest.cpp
   CallGraphTest.cpp
   CaptureTrackingTest.cpp
   CFGTest.cpp
   CGSCCPassManagerTest.cpp
   DivergenceAnalysisTest.cpp
   DomTreeUpdaterTest.cpp
   GlobalsModRefTest.cpp
+  IVDescriptorsTest.cpp
   LazyCallGraphTest.cpp
   LoopInfoTest.cpp
   MemoryBuiltinsTest.cpp
   MemorySSATest.cpp
   OrderedBasicBlockTest.cpp
   OrderedInstructionsTest.cpp
   PhiValuesTest.cpp
   ProfileSummaryInfoTest.cpp
   ScalarEvolutionTest.cpp
   SparsePropagation.cpp
   TargetLibraryInfoTest.cpp
   TBAATest.cpp
   UnrollAnalyzerTest.cpp
   ValueLatticeTest.cpp
   ValueTrackingTest.cpp
   )

llvm/unittests/Analysis/IVDescriptorsTest.cpp

+//===- IVDescriptorsTest.cpp - IVDescriptors unit tests -------------------===//
+//
+// 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/Analysis/IVDescriptors.h"
+#include "llvm/Analysis/AssumptionCache.h"
+#include "llvm/Analysis/LoopInfo.h"
+#include "llvm/Analysis/ScalarEvolution.h"
+#include "llvm/Analysis/TargetLibraryInfo.h"
+#include "llvm/AsmParser/Parser.h"
+#include "llvm/IR/Dominators.h"
+#include "llvm/Support/SourceMgr.h"
+#include "gtest/gtest.h"
+
+using namespace llvm;
+
+/// Build the loop info and scalar evolution for the function and run the Test.
+static void runWithLoopInfoAndSE(
+    Module &M, StringRef FuncName,
+    function_ref<void(Function &F, LoopInfo &LI, ScalarEvolution &SE)> Test) {
+  auto *F = M.getFunction(FuncName);
+  ASSERT_NE(F, nullptr) << "Could not find " << FuncName;
+
+  TargetLibraryInfoImpl TLII;
+  TargetLibraryInfo TLI(TLII);
+  AssumptionCache AC(*F);
+  DominatorTree DT(*F);
+  LoopInfo LI(DT);
+  ScalarEvolution SE(*F, TLI, AC, DT, LI);
+
+  Test(*F, LI, SE);
+}
+
+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("IVDescriptorsTests", errs());
+  return Mod;
+}
+
+// This tests that IVDescriptors can obtain the induction binary operator for
+// integer induction variables. And hasUnsafeAlgebra() and
+// getUnsafeAlgebraInst() correctly return the expected behavior, i.e. no unsafe
+// algebra.
+TEST(IVDescriptorsTest, LoopWithSingleLatch) {
+  // Parse the module.
+  LLVMContext Context;
+
+  std::unique_ptr<Module> M = parseIR(
+    Context,
+    R"(define void @foo(i32* %A, i32 %ub) {
+entry:
+  br label %for.body
+for.body:
+  %i = phi i32 [ 0, %entry ], [ %inc, %for.body ]
+  %idxprom = sext i32 %i to i64
+  %arrayidx = getelementptr inbounds i32, i32* %A, i64 %idxprom
+  store i32 %i, i32* %arrayidx, align 4
+  %inc = add nsw i32 %i, 1
+  %cmp = icmp slt i32 %inc, %ub
+  br i1 %cmp, label %for.body, label %for.exit
+for.exit:
+  br label %for.end
+for.end:
+  ret void
+})"
+    );
+
+  runWithLoopInfoAndSE(
+      *M, "foo", [&](Function &F, LoopInfo &LI, ScalarEvolution &SE) {
+        Function::iterator FI = F.begin();
+        // First basic block is entry - skip it.
+        BasicBlock *Header = &*(++FI);
+        assert(Header->getName() == "for.body");
+        Loop *L = LI.getLoopFor(Header);
+        EXPECT_NE(L, nullptr);
+        PHINode *Inst_i = dyn_cast<PHINode>(&Header->front());
+        assert(Inst_i->getName() == "i");
+        InductionDescriptor IndDesc;
+        bool IsInductionPHI =
+            InductionDescriptor::isInductionPHI(Inst_i, L, &SE, IndDesc);
+        EXPECT_TRUE(IsInductionPHI);
+        Instruction *Inst_inc = nullptr;
+        BasicBlock::iterator BBI = Header->begin();
+        do {
+          if ((&*BBI)->getName() == "inc")
+            Inst_inc = &*BBI;
+          ++BBI;
+        } while (!Inst_inc);
+        assert(Inst_inc->getName() == "inc");
+        EXPECT_EQ(IndDesc.getInductionBinOp(), Inst_inc);
+        EXPECT_FALSE(IndDesc.hasUnsafeAlgebra());
+        EXPECT_EQ(IndDesc.getUnsafeAlgebraInst(), nullptr);
+      });
+}