1 files changed, 21 insertions, 0 deletions
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
index fdef49e..ccf918f 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
@@ -11,11 +11,13 @@
 //===----------------------------------------------------------------------===//
 
 #include "InstCombineInternal.h"
+#include "llvm/ADT/APInt.h"
 #include "llvm/ADT/SetVector.h"
 #include "llvm/Analysis/ConstantFolding.h"
 #include "llvm/IR/DataLayout.h"
 #include "llvm/IR/DebugInfo.h"
 #include "llvm/IR/PatternMatch.h"
+#include "llvm/IR/Value.h"
 #include "llvm/Support/KnownBits.h"
 #include "llvm/Transforms/InstCombine/InstCombiner.h"
 #include <optional>
@@ -969,6 +971,25 @@ Instruction *InstCombinerImpl::visitTrunc(TruncInst &Trunc) {
     Changed = true;
   }
 
+  const APInt *C1;
+  Value *V1;
+  // OP = { lshr, ashr }
+  // trunc ( OP i8 C1, V1) to i1 -> icmp eq V1, log_2(C1) iff C1 is power of 2
+  if (DestWidth == 1 && match(Src, m_Shr(m_Power2(C1), m_Value(V1)))) {
+    Value *Right = ConstantInt::get(V1->getType(), C1->countr_zero());
+    Value *Icmp = Builder.CreateICmpEQ(V1, Right);
+    return replaceInstUsesWith(Trunc, Icmp);
+  }
+
+  // OP = { lshr, ashr }
+  // trunc ( OP i8 C1, V1) to i1 -> icmp ult V1, log_2(C1 + 1) iff (C1 + 1) is
+  // power of 2
+  if (DestWidth == 1 && match(Src, m_Shr(m_LowBitMask(C1), m_Value(V1)))) {
+    Value *Right = ConstantInt::get(V1->getType(), C1->countr_one());
+    Value *Icmp = Builder.CreateICmpULT(V1, Right);
+    return replaceInstUsesWith(Trunc, Icmp);
+  }
+
   return Changed ? &Trunc : nullptr;
 }