ScalarEvolution: Do not keep temporary PHI values in ValueExprMap

Before this patch simplified SCEV expressions for PHI nodes were only returned
the very first time getSCEV() was called, but later calls to getSCEV always
returned the non-simplified value, which had "temporarily" been stored in the
ValueExprMap, but was never removed and consequently blocked the caching of the
simplified PHI expression.

llvm-svn: 261485

diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index 4c3c5c7..6e8fa5d 100644 (file)
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -3897,6 +3897,11 @@ const SCEV *ScalarEvolution::createAddRecFromPHI(PHINode *PN) {
     }
   }
 
+  // Remove the temporary PHI node SCEV that has been inserted while intending
+  // to create an AddRecExpr for this PHI node. We can not keep this temporary
+  // as it will prevent later (possibly simpler) SCEV expressions to be added
+  // to the ValueExprMap.
+  ValueExprMap.erase(PN);
   return nullptr;
 }
 

diff --git a/llvm/unittests/Analysis/ScalarEvolutionTest.cpp b/llvm/unittests/Analysis/ScalarEvolutionTest.cpp
index 938dafe..4089e5d 100644 (file)
--- a/llvm/unittests/Analysis/ScalarEvolutionTest.cpp
+++ b/llvm/unittests/Analysis/ScalarEvolutionTest.cpp
@@ -237,5 +237,31 @@ TEST_F(ScalarEvolutionsTest, SCEVMultiplyAddRecs) {
   EXPECT_EQ(Product->getOperand(8), SE.getAddExpr(Sum));
 }
 
+TEST_F(ScalarEvolutionsTest, SimplifiedPHI) {
+  FunctionType *FTy = FunctionType::get(Type::getVoidTy(Context),
+                                              std::vector<Type *>(), false);
+  Function *F = cast<Function>(M.getOrInsertFunction("f", FTy));
+  BasicBlock *EntryBB = BasicBlock::Create(Context, "entry", F);
+  BasicBlock *LoopBB = BasicBlock::Create(Context, "loop", F);
+  BasicBlock *ExitBB = BasicBlock::Create(Context, "exit", F);
+  BranchInst::Create(LoopBB, EntryBB);
+  BranchInst::Create(LoopBB, ExitBB, UndefValue::get(Type::getInt1Ty(Context)),
+                     LoopBB);
+  ReturnInst::Create(Context, nullptr, ExitBB);
+  auto *Ty = Type::getInt32Ty(Context);
+  auto *PN = PHINode::Create(Ty, 2, "", &*LoopBB->begin());
+  PN->addIncoming(Constant::getNullValue(Ty), EntryBB);
+  PN->addIncoming(UndefValue::get(Ty), LoopBB);
+  ScalarEvolution SE = buildSE(*F);
+  auto *S1 = SE.getSCEV(PN);
+  auto *S2 = SE.getSCEV(PN);
+  assert(isa<SCEVConstant>(S1) && "Expected a SCEV Constant");
+
+  // At some point, only the first call to getSCEV returned the simplified
+  // SCEVConstant and later calls just returned a SCEVUnknown referencing the
+  // PHI node.
+  assert(S1 == S2 && "Expected identical SCEV values");
+}
+
 }  // end anonymous namespace
 }  // end namespace llvm