[PATCH] D111836: [indvars] Use fact loop must exit to canonicalize to unsigned conditions

[Max Kazantsev via Phabricator via llvm-commits]

mkazantsev added inline comments.


================
Comment at: llvm/lib/Transforms/Scalar/IndVarSimplify.cpp:1425
+    return false;
+  auto *BI = dyn_cast<BranchInst>(ExitingBB->getTerminator());
+  if (!BI || BI->isUnconditional())
----------------
Looks like a great place to use pattern matching.


================
Comment at: llvm/test/Transforms/IndVarSimplify/finite-exit-comparisons.ll:304
 ; CHECK-NEXT:    [[ZEXT:%.*]] = zext i8 [[IV_NEXT]] to i16
-; CHECK-NEXT:    [[CMP:%.*]] = icmp sgt i16 [[ZEXT]], 254
+; CHECK-NEXT:    [[CMP:%.*]] = icmp ugt i16 [[ZEXT]], 254
 ; CHECK-NEXT:    br i1 [[CMP]], label [[FOR_BODY]], label [[FOR_END:%.*]]
----------------
Why does it need mustprogress notion to do this at all? Zext is non-negative, 254 is non-negative, we can always do that regardless of mustprogress. We have this logic in `eliminateIVComparison`:

```
  } else if (ICmpInst::isSigned(OriginalPred) &&
             SE->isKnownNonNegative(S) && SE->isKnownNonNegative(X)) {
    // 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));
```
Why it didn't work?


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D111836/new/

https://reviews.llvm.org/D111836