2 files changed, 38 insertions, 0 deletions
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
index 669d4f0..8d9933b 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -582,6 +582,18 @@ static Instruction *foldCttzCtlz(IntrinsicInst &II, InstCombinerImpl &IC) {
           IC.Builder.CreateBinaryIntrinsic(Intrinsic::ctlz, C, Op1);
       return BinaryOperator::CreateSub(ConstCtlz, X);
     }
+
+    // ctlz(~x & (x - 1)) -> bitwidth - cttz(x, false)
+    if (Op0->hasOneUse() &&
+        match(Op0,
+              m_c_And(m_Not(m_Value(X)), m_Add(m_Deferred(X), m_AllOnes())))) {
+      Type *Ty = II.getType();
+      unsigned BitWidth = Ty->getScalarSizeInBits();
+      auto *Cttz = IC.Builder.CreateIntrinsic(Intrinsic::cttz, Ty,
+                                              {X, IC.Builder.getFalse()});
+      auto *Bw = ConstantInt::get(Ty, APInt(BitWidth, BitWidth));
+      return IC.replaceInstUsesWith(II, IC.Builder.CreateSub(Bw, Cttz));
+    }
   }
 
   // cttz(Pow2) -> Log2(Pow2)
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
index 5aa8de3..f5130da 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -4697,5 +4697,31 @@ Instruction *InstCombinerImpl::visitSelectInst(SelectInst &SI) {
                 cast<IntrinsicInst>(TrueVal)->getParamAlign(0).valueOrOne(),
                 CondVal, FalseVal));
 
+  // Canonicalize sign function ashr pattern: select (icmp slt X, 1), ashr X,
+  // bitwidth-1, 1 -> scmp(X, 0)
+  // Also handles: select (icmp sgt X, 0), 1, ashr X, bitwidth-1 -> scmp(X, 0)
+  unsigned BitWidth = SI.getType()->getScalarSizeInBits();
+  CmpPredicate Pred;
+  Value *CmpLHS, *CmpRHS;
+
+  // Canonicalize sign function ashr patterns:
+  // select (icmp slt X, 1), ashr X, bitwidth-1, 1 -> scmp(X, 0)
+  // select (icmp sgt X, 0), 1, ashr X, bitwidth-1 -> scmp(X, 0)
+  if (match(&SI, m_Select(m_ICmp(Pred, m_Value(CmpLHS), m_Value(CmpRHS)),
+                          m_Value(TrueVal), m_Value(FalseVal))) &&
+      ((Pred == ICmpInst::ICMP_SLT && match(CmpRHS, m_One()) &&
+        match(TrueVal,
+              m_AShr(m_Specific(CmpLHS), m_SpecificInt(BitWidth - 1))) &&
+        match(FalseVal, m_One())) ||
+       (Pred == ICmpInst::ICMP_SGT && match(CmpRHS, m_Zero()) &&
+        match(TrueVal, m_One()) &&
+        match(FalseVal,
+              m_AShr(m_Specific(CmpLHS), m_SpecificInt(BitWidth - 1)))))) {
+
+    Function *Scmp = Intrinsic::getOrInsertDeclaration(
+        SI.getModule(), Intrinsic::scmp, {SI.getType(), SI.getType()});
+    return CallInst::Create(Scmp, {CmpLHS, ConstantInt::get(SI.getType(), 0)});
+  }
+
   return nullptr;
 }