3 files changed, 68 insertions, 0 deletions

diff --git a/llvm/include/llvm/Analysis/LazyValueInfo.h b/llvm/include/llvm/Analysis/LazyValueInfo.h
index 7b178fc7bcc..787c88cc6ec 100644
--- a/llvm/include/llvm/Analysis/LazyValueInfo.h
+++ b/llvm/include/llvm/Analysis/LazyValueInfo.h
@@ -93,6 +93,13 @@ public:
   Constant *getConstantOnEdge(Value *V, BasicBlock *FromBB, BasicBlock *ToBB,
                               Instruction *CxtI = nullptr);
 
+  /// Return the ConstantRage constraint that is known to hold for the
+  /// specified value on the specified edge. This may be only be called
+  /// on integer-typed Values.
+  ConstantRange getConstantRangeOnEdge(Value *V, BasicBlock *FromBB,
+                                       BasicBlock *ToBB,
+                                       Instruction *CxtI = nullptr);
+
   /// Inform the analysis cache that we have threaded an edge from
   /// PredBB to OldSucc to be from PredBB to NewSucc instead.
   void threadEdge(BasicBlock *PredBB, BasicBlock *OldSucc, BasicBlock *NewSucc);
diff --git a/llvm/lib/Analysis/LazyValueInfo.cpp b/llvm/lib/Analysis/LazyValueInfo.cpp
index a5d6e670f72..102081e721a 100644
--- a/llvm/lib/Analysis/LazyValueInfo.cpp
+++ b/llvm/lib/Analysis/LazyValueInfo.cpp
@@ -1660,6 +1660,26 @@ Constant *LazyValueInfo::getConstantOnEdge(Value *V, BasicBlock *FromBB,
   return nullptr;
 }
 
+ConstantRange LazyValueInfo::getConstantRangeOnEdge(Value *V,
+                                                    BasicBlock *FromBB,
+                                                    BasicBlock *ToBB,
+                                                    Instruction *CxtI) {
+  unsigned Width = V->getType()->getIntegerBitWidth();
+  const DataLayout &DL = FromBB->getModule()->getDataLayout();
+  LVILatticeVal Result =
+      getImpl(PImpl, AC, &DL, DT).getValueOnEdge(V, FromBB, ToBB, CxtI);
+
+  if (Result.isUndefined())
+    return ConstantRange(Width, /*isFullSet=*/false);
+  if (Result.isConstantRange())
+    return Result.getConstantRange();
+  // We represent ConstantInt constants as constant ranges but other kinds
+  // of integer constants, i.e. ConstantExpr will be tagged as constants
+  assert(!(Result.isConstant() && isa<ConstantInt>(Result.getConstant())) &&
+         "ConstantInt value must be represented as constantrange");
+  return ConstantRange(Width, /*isFullSet=*/true);
+}
+
 static LazyValueInfo::Tristate getPredicateResult(unsigned Pred, Constant *C,
                                                   const LVILatticeVal &Val,
                                                   const DataLayout &DL,
diff --git a/llvm/lib/Transforms/Scalar/JumpThreading.cpp b/llvm/lib/Transforms/Scalar/JumpThreading.cpp
index 011a81e1654..05293eb0079 100644
--- a/llvm/lib/Transforms/Scalar/JumpThreading.cpp
+++ b/llvm/lib/Transforms/Scalar/JumpThreading.cpp
@@ -25,6 +25,7 @@
 #include "llvm/Analysis/Loads.h"
 #include "llvm/Analysis/LoopInfo.h"
 #include "llvm/Analysis/ValueTracking.h"
+#include "llvm/IR/ConstantRange.h"
 #include "llvm/IR/DataLayout.h"
 #include "llvm/IR/IntrinsicInst.h"
 #include "llvm/IR/LLVMContext.h"
@@ -635,6 +636,46 @@ bool JumpThreadingPass::ComputeValueKnownInPredecessors(
         return !Result.empty();
       }
 
+      // InstCombine can fold some forms of constant range checks into
+      // (icmp (add (x, C1)), C2). See if we have we have such a thing with
+      // x as a live-in.
+      {
+        using namespace PatternMatch;
+        Value *AddLHS;
+        ConstantInt *AddConst;
+        if (isa<ConstantInt>(CmpConst) &&
+            match(CmpLHS, m_Add(m_Value(AddLHS), m_ConstantInt(AddConst)))) {
+          if (!isa<Instruction>(AddLHS) ||
+              cast<Instruction>(AddLHS)->getParent() != BB) {
+            for (BasicBlock *P : predecessors(BB)) {
+              // If the value is known by LazyValueInfo to be a ConstantRange in
+              // a predecessor, use that information to try to thread this
+              // block.
+              ConstantRange CR = LVI->getConstantRangeOnEdge(
+                  AddLHS, P, BB, CxtI ? CxtI : cast<Instruction>(CmpLHS));
+              // Propagate the range through the addition.
+              CR = CR.add(AddConst->getValue());
+
+              // Get the range where the compare returns true.
+              ConstantRange CmpRange = ConstantRange::makeExactICmpRegion(
+                  Pred, cast<ConstantInt>(CmpConst)->getValue());
+
+              Constant *ResC;
+              if (CmpRange.contains(CR))
+                ResC = ConstantInt::getTrue(CmpType);
+              else if (CmpRange.inverse().contains(CR))
+                ResC = ConstantInt::getFalse(CmpType);
+              else
+                continue;
+
+              Result.push_back(std::make_pair(ResC, P));
+            }
+
+            return !Result.empty();
+          }
+        }
+      }
+
       // Try to find a constant value for the LHS of a comparison,
       // and evaluate it statically if we can.
       PredValueInfoTy LHSVals;