[InstCombine] fold icmp ne (and X, 1), 0 --> trunc X to N x i1

Author: andjo403

llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp

@@ -1768,11 +1768,8 @@ Instruction *InstCombinerImpl::foldICmpAndConstConst(ICmpInst &Cmp,
                                                      const APInt &C1) {
   bool isICMP_NE = Cmp.getPredicate() == ICmpInst::ICMP_NE;
 
-  // For vectors: icmp ne (and X, 1), 0 --> trunc X to N x i1
-  // TODO: We canonicalize to the longer form for scalars because we have
-  // better analysis/folds for icmp, and codegen may be better with icmp.
-  if (isICMP_NE && Cmp.getType()->isVectorTy() && C1.isZero() &&
-      match(And->getOperand(1), m_One()))
+  // icmp ne (and X, 1), 0 --> trunc X to N x i1
+  if (isICMP_NE && C1.isZero() && match(And->getOperand(1), m_One()))
     return new TruncInst(And->getOperand(0), Cmp.getType());
 
   const APInt *C2;
@@ -6778,6 +6775,13 @@ Instruction *InstCombinerImpl::foldICmpUsingKnownBits(ICmpInst &I) {
     break;
   case ICmpInst::ICMP_EQ:
   case ICmpInst::ICMP_NE: {
+    if (Ty->isIntOrIntVectorTy() && Op0Known.countMaxActiveBits() <= 1)
+      if ((Pred == CmpInst::ICMP_NE && Op1Known.isZero()) ||
+          (Pred == CmpInst::ICMP_EQ && Op1Known.isConstant() &&
+           Op1Known.getConstant().isOne()))
+        return replaceInstUsesWith(
+            I, Builder.CreateTrunc(Op0, I.getType(), "", /*IsNUW=*/true));
+
     // If all bits are known zero except for one, then we know at most one bit
     // is set. If the comparison is against zero, then this is a check to see if
     // *that* bit is set.