[SCEVExpander] Hoist unsigned divisons when safe

That is, when the divisor is a constant non-zero.

llvm-svn: 286438

2 files changed, 16 insertions, 1 deletions

diff --git a/llvm/lib/Analysis/ScalarEvolutionExpander.cpp b/llvm/lib/Analysis/ScalarEvolutionExpander.cpp
index d94782ab899..216a95870a8 100644
--- a/llvm/lib/Analysis/ScalarEvolutionExpander.cpp
+++ b/llvm/lib/Analysis/ScalarEvolutionExpander.cpp
@@ -198,7 +198,9 @@ Value *SCEVExpander::InsertBinop(Instruction::BinaryOps Opcode,
   DebugLoc Loc = Builder.GetInsertPoint()->getDebugLoc();
   SCEVInsertPointGuard Guard(Builder, this);
 
-  if (Opcode != Instruction::UDiv) {
+  auto *RHSConst = dyn_cast<ConstantInt>(RHS);
+
+  if (Opcode != Instruction::UDiv || (RHSConst && !RHSConst->isZero())) {
     // FIXME: There is alredy similar logic in expandCodeFor, we should see if
     // this is actually needed here.
 
diff --git a/llvm/unittests/Analysis/ScalarEvolutionTest.cpp b/llvm/unittests/Analysis/ScalarEvolutionTest.cpp
index f9289250419..bc5b12ae892 100644
--- a/llvm/unittests/Analysis/ScalarEvolutionTest.cpp
+++ b/llvm/unittests/Analysis/ScalarEvolutionTest.cpp
@@ -538,6 +538,19 @@ TEST_F(ScalarEvolutionsTest, BadHoistingSCEVExpander_PR30942) {
       ASSERT_NE(DivFromScratchExpansionInst, nullptr);
       EXPECT_EQ(DivInst->getParent(), DivFromScratchExpansionInst->getParent());
     }
+
+    {
+      auto *ArgY = getArgByName(F, "y");
+      auto *SafeDivSCEV =
+          SE.getUDivExpr(SE.getSCEV(ArgY), SE.getConstant(APInt(32, 19)));
+
+      auto *SafeDivExpansion =
+          Expander.expandCodeFor(SafeDivSCEV, SafeDivSCEV->getType(),
+                                 DivInst->getParent()->getTerminator());
+      auto *SafeDivExpansionInst = dyn_cast<Instruction>(SafeDivExpansion);
+      ASSERT_NE(SafeDivExpansionInst, nullptr);
+      EXPECT_EQ("loop.ph", SafeDivExpansionInst->getParent()->getName());
+    }
   });
 }