[llvm] f492a41 - [SCEV] Simplify forgetSymbolicName() (NFCI)

[Nikita Popov via llvm-commits]

Author: Nikita Popov
Date: 2021-11-27T16:42:38+01:00
New Revision: f492a414bad782ae4202d2af9d3408f8e727599d

URL: https://github.com/llvm/llvm-project/commit/f492a414bad782ae4202d2af9d3408f8e727599d
DIFF: https://github.com/llvm/llvm-project/commit/f492a414bad782ae4202d2af9d3408f8e727599d.diff

LOG: [SCEV] Simplify forgetSymbolicName() (NFCI)

With the recently introduced tracking as well as 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 is needed to also clear out the
actual IR to SCEV mapping in ValueExprMap.

Differential Revision: https://reviews.llvm.org/D114263

Added: 
    

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

Removed: 
    


################################################################################
diff  --git a/llvm/include/llvm/Analysis/ScalarEvolution.h b/llvm/include/llvm/Analysis/ScalarEvolution.h
index 4cfbf49bbc862..3051204f4c5b7 100644
--- a/llvm/include/llvm/Analysis/ScalarEvolution.h
+++ b/llvm/include/llvm/Analysis/ScalarEvolution.h
@@ -1616,11 +1616,6 @@ class ScalarEvolution {
   /// 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.

diff  --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index 76af5a6d16172..f41b89517abcb 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -4442,42 +4442,6 @@ static void PushDefUseChildren(Instruction *I,
   }
 }
 
-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
@@ -5469,7 +5433,7 @@ const SCEV *ScalarEvolution::createAddRecFromPHI(PHINode *PN) {
         // 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
@@ -5501,7 +5465,7 @@ const SCEV *ScalarEvolution::createAddRecFromPHI(PHINode *PN) {
         // 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;
       }