1 files changed, 41 insertions, 0 deletions
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;