[llvm] [InstCombine] Added optimisation for trunc (Pow2 >> x) to i1 (PR #157030)

[Andreas Jonson via llvm-commits]

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@@ -969,6 +971,25 @@ Instruction *InstCombinerImpl::visitTrunc(TruncInst &Trunc) {
     Changed = true;
   }
 
+  const APInt *C1;
+  Value *V1;
+  // trunc (lshr i8 C1, V1) to i1 -> icmp eq V1, log_2(C1) iff C1 is power of 2
+  if (DestWidth == 1 &&
+      match(Src, m_OneUse(m_Shr(m_Power2(C1), m_Value(V1))))) {
+    Value *Right = ConstantInt::get(V1->getType(), C1->nearestLogBase2());
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andjo403 wrote:

seems like countr_zero is used instead of nearestLogBase2

https://github.com/llvm/llvm-project/pull/157030