[llvm] [SimplifyIndVar] ICMP predicate conversion to EQ/NE (PR #144945)

[Philip Reames via llvm-commits]

================
@@ -267,33 +390,43 @@ void SimplifyIndvar::eliminateIVComparison(ICmpInst *ICmp,
   // If the condition is always true or always false in the given context,
   // replace it with a constant value.
   SmallVector<Instruction *, 4> Users;
+  bool IsDead = false;
   for (auto *U : ICmp->users())
     Users.push_back(cast<Instruction>(U));
   const Instruction *CtxI = findCommonDominator(Users, *DT);
   if (auto Ev = SE->evaluatePredicateAt(Pred, S, X, CtxI)) {
     SE->forgetValue(ICmp);
     ICmp->replaceAllUsesWith(ConstantInt::getBool(ICmp->getContext(), *Ev));
     DeadInsts.emplace_back(ICmp);
+    IsDead = true;
     LLVM_DEBUG(dbgs() << "INDVARS: Eliminated comparison: " << *ICmp << '\n');
   } else if (makeIVComparisonInvariant(ICmp, IVOperand)) {
-    // fallthrough to end of function
-  } else if (ICmpInst::isSigned(OriginalPred) &&
-             SE->isKnownNonNegative(S) && SE->isKnownNonNegative(X)) {
+    IsDead = true;
+  } else {
     // If we were unable to make anything above, all we can is to canonicalize
     // the comparison hoping that it will open the doors for other
-    // optimizations. If we find out that we compare two non-negative values,
-    // we turn the instruction's predicate to its unsigned version. Note that
-    // we cannot rely on Pred here unless we check if we have swapped it.
-    assert(ICmp->getPredicate() == OriginalPred && "Predicate changed?");
-    LLVM_DEBUG(dbgs() << "INDVARS: Turn to unsigned comparison: " << *ICmp
-                      << '\n');
-    ICmp->setPredicate(ICmpInst::getUnsignedPredicate(OriginalPred));
-    ICmp->setSameSign();
-  } else
-    return;
+    // optimizations.
+    if (ICmpInst::isSigned(OriginalPred) && SE->isKnownNonNegative(S) &&
+        SE->isKnownNonNegative(X)) {
+      // If we find out that we compare two non-negative values,
+      // we turn the instruction's predicate to its unsigned version. Note that
+      // we cannot rely on Pred here unless we check if we have swapped it.
+      assert(ICmp->getPredicate() == OriginalPred && "Predicate changed?");
+      LLVM_DEBUG(dbgs() << "INDVARS: Turn to unsigned comparison: " << *ICmp
+                        << '\n');
+      ICmp->setPredicate(ICmpInst::getUnsignedPredicate(OriginalPred));
+      ICmp->setSameSign();
+      Changed = true;
+    }
+    if (forceEqualityForICmp(ICmp, IVOperand)) {
+      Changed = true;
+    }
+  }
 
-  ++NumElimCmp;
-  Changed = true;
+  if (IsDead) {
----------------
preames wrote:

See https://github.com/llvm/llvm-project/pull/170514

https://github.com/llvm/llvm-project/pull/144945