[PATCH] D143409: [SCEV][IndVarSimplify] Support known dominating slt/ult elimination

[Max Kazantsev via Phabricator via llvm-commits]

mkazantsev requested changes to this revision.
mkazantsev added inline comments.
This revision now requires changes to proceed.


================
Comment at: llvm/lib/Analysis/ScalarEvolution.cpp:11115
+    // - If ArLHS is negative, 'ArLHS <u RHS' will be false on the first
+    // iteration
+    if (isKnownPositive(ArLHS->getStepRecurrence(*this)) &&
----------------
Sure this is wrong.
```
start = SINT_MAX - 1
step = 2
RHS = SINT_MAX
```

On first iteration, both checks pass.
```
SINT_MAX - 1 <s SINT_MAX // true
SINT_MAX - 1 <u SINT_MAX // true
```
On the 2nd iteration unsigned check will fail.
SINT_MAX + 1 <s SINT_MAX // true
SINT_MAX + 1 <u SINT_MAX  // false

Note that what you did is just duplicated the checks above, but dropped the `nuw` check that was there for reason.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D143409/new/

https://reviews.llvm.org/D143409