1 files changed, 24 insertions, 0 deletions
diff --git a/contrib/llvm-project/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/contrib/llvm-project/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
index 96b612254ca5..c7e6f32c5406 100644
--- a/contrib/llvm-project/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ b/contrib/llvm-project/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -1723,6 +1723,30 @@ Instruction *InstCombinerImpl::visitAdd(BinaryOperator &I) {
         I, Builder.CreateIntrinsic(Intrinsic::ctpop, {I.getType()},
                                    {Builder.CreateOr(A, B)}));
 
+  // Fold the log2_ceil idiom:
+  // zext(ctpop(A) >u/!= 1) + (ctlz(A, true) ^ (BW - 1))
+  // -->
+  // BW - ctlz(A - 1, false)
+  const APInt *XorC;
+  if (match(&I,
+            m_c_Add(
+                m_ZExt(m_ICmp(Pred, m_Intrinsic<Intrinsic::ctpop>(m_Value(A)),
+                              m_One())),
+                m_OneUse(m_ZExtOrSelf(m_OneUse(m_Xor(
+                    m_OneUse(m_TruncOrSelf(m_OneUse(
+                        m_Intrinsic<Intrinsic::ctlz>(m_Deferred(A), m_One())))),
+                    m_APInt(XorC))))))) &&
+      (Pred == ICmpInst::ICMP_UGT || Pred == ICmpInst::ICMP_NE) &&
+      *XorC == A->getType()->getScalarSizeInBits() - 1) {
+    Value *Sub = Builder.CreateAdd(A, Constant::getAllOnesValue(A->getType()));
+    Value *Ctlz = Builder.CreateIntrinsic(Intrinsic::ctlz, {A->getType()},
+                                          {Sub, Builder.getFalse()});
+    Value *Ret = Builder.CreateSub(
+        ConstantInt::get(A->getType(), A->getType()->getScalarSizeInBits()),
+        Ctlz, "", /*HasNUW*/ true, /*HasNSW*/ true);
+    return replaceInstUsesWith(I, Builder.CreateZExtOrTrunc(Ret, I.getType()));
+  }
+
   if (Instruction *Res = foldSquareSumInt(I))
     return Res;