[PATCH] D30887: [ScalarEvolution] Predicate implication from operations

[Max Kazantsev via Phabricator via llvm-commits]

mkazantsev added inline comments.


================
Comment at: lib/Analysis/ScalarEvolution.cpp:8527
+    auto *Zero = getZero(RHS->getType());
+    auto *LLExt = getNoopOrSignExtend(LL, OrigLHS->getType());
+    auto *LRExt = getNoopOrSignExtend(LR, OrigLHS->getType());
----------------
sanjoy wrote:
> Can we get what we want here without sign extension?  As I've said below, sign extension can be expensive.
> 
> In fact, it would be surprising if we see `LHS` is not the same as `OrigLHS` since that would mean a `sext (%a + %b)<nsw>` did not get transformed to `(sext %a + sext %b)<nsw>` as per the rule in `ScalarEvolution::getSignExtendExpr`.  That situation is possible, but should be rare.
Why is it rare? We can calculate sdiv i32 %a, %b and than use it in multiple ways, one of them being comparison to an i64 constant. In this case we will see exactly this.


https://reviews.llvm.org/D30887