[llvm] [InstCombine] Fold (X / C) < X and (X >> C) < X into X > 0 (PR #85555)

[via llvm-commits]

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@@ -7103,6 +7103,37 @@ Instruction *InstCombinerImpl::foldICmpCommutative(ICmpInst::Predicate Pred,
   if (Value *V = foldICmpWithLowBitMaskedVal(Pred, Op0, Op1, Q, *this))
     return replaceInstUsesWith(CxtI, V);
 
+  // Folding (X / Y) pred X => X ~pred 0 for some constant Y other than 0 or 1
+  {
+    const APInt *Divisor;
+    if (match(Op0, m_UDiv(m_Specific(Op1), m_APInt(Divisor))) &&
+        Divisor->ugt(1)) {
+      return new ICmpInst(ICmpInst::getSwappedPredicate(Pred), Op1,
+                          Constant::getNullValue(Op1->getType()));
+    }
+
+    if (match(Op0, m_SDiv(m_Specific(Op1), m_APInt(Divisor))) &&
+        Divisor->ugt(1) && !ICmpInst::isUnsigned(Pred)) {
+      return new ICmpInst(ICmpInst::getSwappedPredicate(Pred), Op1,
+                          Constant::getNullValue(Op1->getType()));
+    }
+  }
+
+  // Another case of this fold is (X >> Y) pred X => X ~pred 0 if Y != 0
+  {
+    const APInt *Shift;
+    if (match(Op0, m_LShr(m_Specific(Op1), m_APInt(Shift))) && Shift->ugt(0)) {
+      return new ICmpInst(ICmpInst::getSwappedPredicate(Pred), Op1,
+                          Constant::getNullValue(Op1->getType()));
+    }
+
+    if (match(Op0, m_AShr(m_Specific(Op1), m_APInt(Shift))) && Shift->ugt(0) &&
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Poseydon42 wrote:

I believe it is fixed now.

https://github.com/llvm/llvm-project/pull/85555