[PATCH] D114263: [SCEV] Simplify forgetSymbolicName() (NFCI)

[Nikita Popov via Phabricator via llvm-commits]

nikic created this revision.
nikic added reviewers: reames, mkazantsev.
Herald added subscribers: javed.absar, hiraditya.
nikic requested review of this revision.
Herald added a project: LLVM.
Herald added a subscriber: llvm-commits.

With the recently introduced tracking as well as D113349 <https://reviews.llvm.org/D113349>, we can greatly simplify forgetSymbolicName(). In fact, we can simply replace it with forgetMemoizedResults().

What forgetSymbolicName() used to do is to walk the IR use-def chain to find all SCEVs that mention the SymbolicName. However, thanks to use tracking, we can now determine the relevant SCEVs in a more direct way. D113349 <https://reviews.llvm.org/D113349> is needed to also clear out the actual IR to SCEV mapping in ValueExprMap.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D114263

Files:
  llvm/include/llvm/Analysis/ScalarEvolution.h
  llvm/lib/Analysis/ScalarEvolution.cpp


Index: llvm/lib/Analysis/ScalarEvolution.cpp
===================================================================
--- llvm/lib/Analysis/ScalarEvolution.cpp
+++ llvm/lib/Analysis/ScalarEvolution.cpp
@@ -4421,42 +4421,6 @@
   }
 }
 
-void ScalarEvolution::forgetSymbolicName(Instruction *PN, const SCEV *SymName) {
-  SmallVector<Instruction *, 16> Worklist;
-  SmallPtrSet<Instruction *, 8> Visited;
-  SmallVector<const SCEV *, 8> ToForget;
-  Visited.insert(PN);
-  Worklist.push_back(PN);
-  while (!Worklist.empty()) {
-    Instruction *I = Worklist.pop_back_val();
-
-    auto It = ValueExprMap.find_as(static_cast<Value *>(I));
-    if (It != ValueExprMap.end()) {
-      const SCEV *Old = It->second;
-
-      // Short-circuit the def-use traversal if the symbolic name
-      // ceases to appear in expressions.
-      if (Old != SymName && !hasOperand(Old, SymName))
-        continue;
-
-      // SCEVUnknown for a PHI either means that it has an unrecognized
-      // structure, it's a PHI that's in the progress of being computed
-      // by createNodeForPHI, or it's a single-value PHI. In the first case,
-      // additional loop trip count information isn't going to change anything.
-      // In the second case, createNodeForPHI will perform the necessary
-      // updates on its own when it gets to that point. In the third, we do
-      // want to forget the SCEVUnknown.
-      if (!isa<PHINode>(I) || !isa<SCEVUnknown>(Old) || Old == SymName) {
-        eraseValueFromMap(It->first);
-        ToForget.push_back(Old);
-      }
-    }
-
-    PushDefUseChildren(I, Worklist, Visited);
-  }
-  forgetMemoizedResults(ToForget);
-}
-
 namespace {
 
 /// Takes SCEV S and Loop L. For each AddRec sub-expression, use its start
@@ -5452,7 +5416,7 @@
         // Okay, for the entire analysis of this edge we assumed the PHI
         // to be symbolic.  We now need to go back and purge all of the
         // entries for the scalars that use the symbolic expression.
-        forgetSymbolicName(PN, SymbolicName);
+        forgetMemoizedResults(SymbolicName);
         insertValueToMap(PN, PHISCEV);
 
         // We can add Flags to the post-inc expression only if we
@@ -5484,7 +5448,7 @@
         // Okay, for the entire analysis of this edge we assumed the PHI
         // to be symbolic.  We now need to go back and purge all of the
         // entries for the scalars that use the symbolic expression.
-        forgetSymbolicName(PN, SymbolicName);
+        forgetMemoizedResults(SymbolicName);
         insertValueToMap(PN, Shifted);
         return Shifted;
       }
Index: llvm/include/llvm/Analysis/ScalarEvolution.h
===================================================================
--- llvm/include/llvm/Analysis/ScalarEvolution.h
+++ llvm/include/llvm/Analysis/ScalarEvolution.h
@@ -1616,11 +1616,6 @@
   /// SCEV+Loop pair.
   const SCEV *computeSCEVAtScope(const SCEV *S, const Loop *L);
 
-  /// This looks up computed SCEV values for all instructions that depend on
-  /// the given instruction and removes them from the ValueExprMap map if they
-  /// reference SymName. This is used during PHI resolution.
-  void forgetSymbolicName(Instruction *I, const SCEV *SymName);
-
   /// Return the BackedgeTakenInfo for the given loop, lazily computing new
   /// values if the loop hasn't been analyzed yet. The returned result is
   /// guaranteed not to be predicated.


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