[PATCH] D38814: [SCEV] Properly handle the case of a non-constant start with a zero accum in ScalarEvolution::createAddRecFromPHIWithCastsImpl

[Daniel Neilson via Phabricator via llvm-commits]

This revision was automatically updated to reflect the committed changes.
Closed by commit rL315491: [SCEV] Properly handle the case of a non-constant start with a zero accum in… (authored by dneilson).

Repository:
  rL LLVM

https://reviews.llvm.org/D38814

Files:
  llvm/trunk/lib/Analysis/ScalarEvolution.cpp
  llvm/trunk/unittests/Analysis/ScalarEvolutionTest.cpp


Index: llvm/trunk/lib/Analysis/ScalarEvolution.cpp
===================================================================
--- llvm/trunk/lib/Analysis/ScalarEvolution.cpp
+++ llvm/trunk/lib/Analysis/ScalarEvolution.cpp
@@ -4523,8 +4523,7 @@
                : SCEVWrapPredicate::IncrementNUSW;
     const SCEVPredicate *AddRecPred = getWrapPredicate(AR, AddedFlags);
     Predicates.push_back(AddRecPred);
-  } else
-    assert(isa<SCEVConstant>(PHISCEV) && "Expected constant SCEV");
+  }
 
   // Create the Equal Predicates P2,P3:
 
Index: llvm/trunk/unittests/Analysis/ScalarEvolutionTest.cpp
===================================================================
--- llvm/trunk/unittests/Analysis/ScalarEvolutionTest.cpp
+++ llvm/trunk/unittests/Analysis/ScalarEvolutionTest.cpp
@@ -1009,6 +1009,63 @@
   auto Result = SE.createAddRecFromPHIWithCasts(cast<SCEVUnknown>(Expr));
 }
 
+TEST_F(ScalarEvolutionsTest, SCEVAddRecFromPHIwithLargeConstantAccum) {
+  // Make sure that SCEV does not blow up when constructing an AddRec
+  // with predicates for a phi with the update pattern:
+  //  (SExt/ZExt ix (Trunc iy (%SymbolicPHI) to ix) to iy) + InvariantAccum
+  // when the InvariantAccum is a constant that is too large to fit in an
+  // ix but are zero when truncated to ix, and the initial value of the
+  // phi is not a constant.
+  Type *Int32Ty = Type::getInt32Ty(Context);
+  SmallVector<Type *, 1> Types;
+  Types.push_back(Int32Ty);
+  FunctionType *FTy = FunctionType::get(Type::getVoidTy(Context), Types, false);
+  Function *F = cast<Function>(M.getOrInsertFunction("addrecphitest", FTy));
+
+  /*
+    Create IR:
+    define @addrecphitest(i32)
+    entry:
+     br label %loop
+    loop:
+     %1 = phi i32 [%0, %entry], [%4, %loop]
+     %2 = shl i32 %1, 16
+     %3 = ashr exact i32 %2, 16
+     %4 = add i32 %3, -2147483648
+     br i1 undef, label %exit, label %loop
+    exit:
+     ret void
+   */
+  BasicBlock *EntryBB = BasicBlock::Create(Context, "entry", F);
+  BasicBlock *LoopBB = BasicBlock::Create(Context, "loop", F);
+  BasicBlock *ExitBB = BasicBlock::Create(Context, "exit", F);
+
+  // entry:
+  BranchInst::Create(LoopBB, EntryBB);
+  // loop:
+  auto *MinInt32 = ConstantInt::get(Context, APInt(32, 0x80000000U, true));
+  auto *Int32_16 = ConstantInt::get(Context, APInt(32, 16));
+  auto *Br = BranchInst::Create(
+      LoopBB, ExitBB, UndefValue::get(Type::getInt1Ty(Context)), LoopBB);
+  auto *Phi = PHINode::Create(Int32Ty, 2, "", Br);
+  auto *Shl = BinaryOperator::CreateShl(Phi, Int32_16, "", Br);
+  auto *AShr = BinaryOperator::CreateExactAShr(Shl, Int32_16, "", Br);
+  auto *Add = BinaryOperator::CreateAdd(AShr, MinInt32, "", Br);
+  auto *Arg = &*(F->arg_begin());
+  Phi->addIncoming(Arg, EntryBB);
+  Phi->addIncoming(Add, LoopBB);
+  // exit:
+  ReturnInst::Create(Context, nullptr, ExitBB);
+
+  // Make sure that SCEV doesn't blow up
+  ScalarEvolution SE = buildSE(*F);
+  SCEVUnionPredicate Preds;
+  const SCEV *Expr = SE.getSCEV(Phi);
+  EXPECT_NE(nullptr, Expr);
+  EXPECT_TRUE(isa<SCEVUnknown>(Expr));
+  auto Result = SE.createAddRecFromPHIWithCasts(cast<SCEVUnknown>(Expr));
+}
+
 TEST_F(ScalarEvolutionsTest, SCEVFoldSumOfTruncs) {
   // Verify that the following SCEV gets folded to a zero:
   //  (-1 * (trunc i64 (-1 * %0) to i32)) + (-1 * (trunc i64 %0 to i32)
@@ -1035,7 +1092,6 @@
   const auto *B = SE.getNegativeSCEV(B0);
 
   const auto *Expr = SE.getAddExpr(A, B);
-  dbgs() << "DDN\nExpr: " << *Expr << "\n";
   // Verify that the SCEV was folded to 0
   const auto *ZeroConst = SE.getConstant(Int32Ty, 0);
   EXPECT_EQ(Expr, ZeroConst);


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