[PATCH] D109782: [SCEV] Stop applying contextual flags in applyLoopGuards

[Philip Reames via Phabricator via llvm-commits]

This revision was landed with ongoing or failed builds.
This revision was automatically updated to reflect the committed changes.
Closed by commit rG0dd755f02742: [SCEV] Stop applying contextual flags in applyLoopGuards (authored by reames).

Changed prior to commit:
  https://reviews.llvm.org/D109782?vs=372550&id=372564#toc

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D109782/new/

https://reviews.llvm.org/D109782

Files:
  llvm/lib/Analysis/ScalarEvolution.cpp


Index: llvm/lib/Analysis/ScalarEvolution.cpp
===================================================================
--- llvm/lib/Analysis/ScalarEvolution.cpp
+++ llvm/lib/Analysis/ScalarEvolution.cpp
@@ -13495,6 +13495,11 @@
 const SCEV *ScalarEvolution::applyLoopGuards(const SCEV *Expr, const Loop *L) {
   auto CollectCondition = [&](ICmpInst::Predicate Predicate, const SCEV *LHS,
                               const SCEV *RHS, ValueToSCEVMapTy &RewriteMap) {
+    // WARNING: It is generally unsound to apply any wrap flags to the proposed
+    // replacement SCEV which isn't directly implied by the structure of that
+    // SCEV.  In particular, using contextual facts to imply flags is *NOT*
+    // legal.  See the scoping rules for flags in the header to understand why.
+
     // If we have LHS == 0, check if LHS is computing a property of some unknown
     // SCEV %v which we can rewrite %v to express explicitly.
     const SCEVConstant *RHSC = dyn_cast<SCEVConstant>(RHS);
@@ -13507,10 +13512,7 @@
       if (matchURem(LHS, URemLHS, URemRHS)) {
         if (const SCEVUnknown *LHSUnknown = dyn_cast<SCEVUnknown>(URemLHS)) {
           Value *V = LHSUnknown->getValue();
-          auto Multiple =
-              getMulExpr(getUDivExpr(URemLHS, URemRHS), URemRHS,
-                         (SCEV::NoWrapFlags)(SCEV::FlagNUW | SCEV::FlagNSW));
-          RewriteMap[V] = Multiple;
+          RewriteMap[V] = getMulExpr(getUDivExpr(URemLHS, URemRHS), URemRHS);
           return;
         }
       }


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