Reland "[SCEV] Model ptrtoint(SCEVUnknown) cast not as unknown, but as zext/trunc/self of SCEVUnknown"

This relands commit 1c021c64caef83cccb719c9bf0a2554faa6563af which was
reverted in commit 17cec6a11a12f815052d56a17ef738cf246a2d9a because
an assertion was being triggered, since `BuildConstantFromSCEV()`
wasn't updated to handle the case where the constant we want to truncate
is actually a pointer. I was unsuccessful in coming up with a test case
where we'd end there with constant zext/sext of a pointer,
so i didn't handle those cases there until there is a test case.

Original commit message:

While we indeed can't treat them as no-ops, i believe we can/should
do better than just modelling them as `unknown`. `inttoptr` story
is complicated, but for `ptrtoint`, it seems straight-forward
to model it just as a zext-or-trunc of unknown.

This may be important now that we track towards
making inttoptr/ptrtoint casts not no-op,
and towards preventing folding them into loads/etc
(see D88979/D88789/D88788)

Reviewed By: mkazantsev

Differential Revision: https://reviews.llvm.org/D88806

1 files changed, 1 insertions, 1 deletions

diff --git a/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp b/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp
index 2d71b0f..3e280a6 100644
--- a/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp
@@ -427,7 +427,7 @@ static bool willNotOverflow(ScalarEvolution *SE, Instruction::BinaryOps BinOp,
              : &ScalarEvolution::getZeroExtendExpr;
 
   // Check ext(LHS op RHS) == ext(LHS) op ext(RHS)
-  auto *NarrowTy = cast<IntegerType>(LHS->getType());
+  auto *NarrowTy = cast<IntegerType>(SE->getEffectiveSCEVType(LHS->getType()));
   auto *WideTy =
     IntegerType::get(NarrowTy->getContext(), NarrowTy->getBitWidth() * 2);