[PATCH] D109546: [ScalarEvolution] Add an additional bailout to avoid NOT of pointer.

[Philip Reames via Phabricator via llvm-commits]

reames created this revision.
reames added reviewers: efriedma, mkazantsev, nikic.
Herald added subscribers: javed.absar, bollu, hiraditya, mcrosier.
reames requested review of this revision.
Herald added a project: LLVM.

It's possible in some cases for the LHS to be a pointer where the RHS is not. This isn't directly possible for an icmp, but the analysis mixes up operands of different icmp expressions in some cases.

This does not include a test case as the smallest reduced case we've managed is extremely fragile and unlikely to test anything meaningful in the long term.

Also add an assertion to getNotSCEV() to make tracking down this sort of issue a bit easier in the future.

Fixes https://bugs.llvm.org/show_bug.cgi?id=51787 .  This is the alternate patch mentioned in D109477 <https://reviews.llvm.org/D109477>.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D109546

Files:
  llvm/lib/Analysis/ScalarEvolution.cpp


Index: llvm/lib/Analysis/ScalarEvolution.cpp
===================================================================
--- llvm/lib/Analysis/ScalarEvolution.cpp
+++ llvm/lib/Analysis/ScalarEvolution.cpp
@@ -4127,6 +4127,8 @@
 
 /// Return a SCEV corresponding to ~V = -1-V
 const SCEV *ScalarEvolution::getNotSCEV(const SCEV *V) {
+  assert(!V->getType()->isPointerTy() && "Can't negate pointer");
+
   if (const SCEVConstant *VC = dyn_cast<SCEVConstant>(V))
     return getConstant(
                 cast<ConstantInt>(ConstantExpr::getNot(VC->getValue())));
@@ -10672,15 +10674,21 @@
     if (!isa<SCEVConstant>(FoundRHS) && !isa<SCEVAddRecExpr>(FoundLHS))
       return isImpliedCondOperands(Pred, LHS, RHS, FoundRHS, FoundLHS, Context);
 
-    // Don't try to getNotSCEV pointers.
-    if (LHS->getType()->isPointerTy() || FoundLHS->getType()->isPointerTy())
-      return false;
+    // There's no clear preference between forms 3. and 4., try both.  Avoid
+    // forming getNotSCEV of pointer values as the resulting subtract is
+    // not legal.
+    if (!LHS->getType()->isPointerTy() && !RHS->getType()->isPointerTy() &&
+        isImpliedCondOperands(FoundPred, getNotSCEV(LHS), getNotSCEV(RHS),
+                              FoundLHS, FoundRHS, Context))
+      return true;
 
-    // There's no clear preference between forms 3. and 4., try both.
-    return isImpliedCondOperands(FoundPred, getNotSCEV(LHS), getNotSCEV(RHS),
-                                 FoundLHS, FoundRHS, Context) ||
-           isImpliedCondOperands(Pred, LHS, RHS, getNotSCEV(FoundLHS),
-                                 getNotSCEV(FoundRHS), Context);
+    if (!FoundLHS->getType()->isPointerTy() &&
+        !FoundRHS->getType()->isPointerTy() &&
+        isImpliedCondOperands(Pred, LHS, RHS, getNotSCEV(FoundLHS),
+                              getNotSCEV(FoundRHS), Context))
+      return true;
+
+    return false;
   }
 
   // Unsigned comparison is the same as signed comparison when both the operands


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