[llvm] [InstCombine] Fold vector.reduce.OP(F(X)) == 0 -> OP(X) == 0 (PR #173069)

[Yingwei Zheng via llvm-commits]

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@@ -3790,6 +3793,139 @@ static Instruction *foldCtpopPow2Test(ICmpInst &I, IntrinsicInst *CtpopLhs,
   return nullptr;
 }
 
+static bool isNullOrPoison(Constant *C) {
+  const auto Pred = [](Constant *X) {
+    return X->isNullValue() || isa<UndefValue>(X) || isa<PoisonValue>(X);
+  };
+
+  if (auto *VecC = dyn_cast<ConstantVector>(C)) {
+    for (unsigned I = 0; I < VecC->getNumOperands(); ++I) {
+      if (Pred(VecC->getOperand(I)))
+        return true;
+    }
+    return false;
+  }
+
+  if (auto *DataVec = dyn_cast<ConstantDataVector>(C)) {
+    for (unsigned I = 0; I < DataVec->getNumElements(); ++I) {
+      if (Pred(DataVec->getElementAsConstant(I)))
+        return true;
+    }
+    return false;
+  }
+
+  return Pred(C);
+}
+
+Instruction *
+InstCombinerImpl::foldICmpEqZeroVectorReduceIntrinsic(ICmpInst &Cmp,
+                                                      IntrinsicInst *II) {
+  // vector.reduce.OP f(X_i) == 0 -> vector.reduce.OP X_i == 0
+  //
+  // We can prove it for cases when:
+  //
+  //   1.  OP X_i == 0 <=> \forall i \in [1, N] X_i == 0
+  //   1'. OP X_i == 0 <=> \exists j \in [1, N] X_j == 0
+  //   2.  f(x) == 0 <=> x == 0
+  //
+  // From 1 and 2 (or 1' and 2), we can infer that
+  //
+  //   OP f(X_i) == 0 <=> OP X_i == 0.
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dtcxzyw wrote:

Can we extend and reuse the `stripNullTest` helper in ValueTracking?

https://github.com/llvm/llvm-project/pull/173069