[PATCH] D149323: [SCEV] Don't invalidate past dependency-breaking instructions

[Nikita Popov via Phabricator via llvm-commits]

nikic updated this revision to Diff 517858.
nikic added a comment.

Add assertion to make sure the assumption about SCEVUnknown is correct.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D149323/new/

https://reviews.llvm.org/D149323

Files:
  llvm/lib/Analysis/ScalarEvolution.cpp


Index: llvm/lib/Analysis/ScalarEvolution.cpp
===================================================================
--- llvm/lib/Analysis/ScalarEvolution.cpp
+++ llvm/lib/Analysis/ScalarEvolution.cpp
@@ -4490,6 +4490,18 @@
   }
 }
 
+/// Determine whether this instruction is either not SCEVable or will always
+/// produce a SCEVUnknown. We do not have to walk past such instructions when
+/// invalidating.
+static bool isAlwaysUnknown(const Instruction *I) {
+  switch (I->getOpcode()) {
+  case Instruction::Load:
+    return true;
+  default:
+    return false;
+  }
+}
+
 /// Return an existing SCEV if it exists, otherwise analyze the expression and
 /// create a new one.
 const SCEV *ScalarEvolution::getSCEV(Value *V) {
@@ -4497,7 +4509,11 @@
 
   if (const SCEV *S = getExistingSCEV(V))
     return S;
-  return createSCEVIter(V);
+  const SCEV *S = createSCEVIter(V);
+  assert((!isa<Instruction>(V) || !isAlwaysUnknown(cast<Instruction>(V)) ||
+          isa<SCEVUnknown>(S)) &&
+         "isAlwaysUnknown() instruction is not SCEVUnknown");
+  return S;
 }
 
 const SCEV *ScalarEvolution::getExistingSCEV(Value *V) {
@@ -4798,6 +4814,8 @@
   // Push the def-use children onto the Worklist stack.
   for (User *U : I->users()) {
     auto *UserInsn = cast<Instruction>(U);
+    if (isAlwaysUnknown(UserInsn))
+      continue;
     if (Visited.insert(UserInsn).second)
       Worklist.push_back(UserInsn);
   }


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