[llvm] 17c20a6 - [SCEV] Avoid unnecessary domination checks (NFC)

[Nikita Popov via llvm-commits]

Author: Nikita Popov
Date: 2021-10-06T22:14:04+02:00
New Revision: 17c20a6dfb7c89ac4eb13990308b731263345918

URL: https://github.com/llvm/llvm-project/commit/17c20a6dfb7c89ac4eb13990308b731263345918
DIFF: https://github.com/llvm/llvm-project/commit/17c20a6dfb7c89ac4eb13990308b731263345918.diff

LOG: [SCEV] Avoid unnecessary domination checks (NFC)

When determining the defining scope, avoid repeatedly querying
dominationg against the function entry instruction. This ends up
begin a very common case that we can handle more efficiently.

Added: 
    

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

Removed: 
    


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diff  --git a/llvm/include/llvm/Analysis/ScalarEvolution.h b/llvm/include/llvm/Analysis/ScalarEvolution.h
index df1b7c2ad157..a38b1a299163 100644
--- a/llvm/include/llvm/Analysis/ScalarEvolution.h
+++ b/llvm/include/llvm/Analysis/ScalarEvolution.h
@@ -1921,9 +1921,10 @@ class ScalarEvolution {
   SCEV::NoWrapFlags getNoWrapFlagsFromUB(const Value *V);
 
   /// Return a scope which provides an upper bound on the defining scope of
-  /// 'S'.  Specifically, return the first instruction in said bounding scope.
+  /// 'S'. Specifically, return the first instruction in said bounding scope.
+  /// Return nullptr if the scope is trivial (function entry).
   /// (See scope definition rules associated with flag discussion above)
-  const Instruction *getDefiningScopeBound(const SCEV *S);
+  const Instruction *getNonTrivialDefiningScopeBound(const SCEV *S);
 
   /// Return a scope which provides an upper bound on the defining scope for
   /// a SCEV with the operands in Ops.

diff  --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index b767adac6a59..14f5dd51c406 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -6585,25 +6585,24 @@ SCEV::NoWrapFlags ScalarEvolution::getNoWrapFlagsFromUB(const Value *V) {
   return isSCEVExprNeverPoison(BinOp) ? Flags : SCEV::FlagAnyWrap;
 }
 
-const Instruction *ScalarEvolution::getDefiningScopeBound(const SCEV *S) {
+const Instruction *
+ScalarEvolution::getNonTrivialDefiningScopeBound(const SCEV *S) {
   if (auto *AddRec = dyn_cast<SCEVAddRecExpr>(S))
     return &*AddRec->getLoop()->getHeader()->begin();
   if (auto *U = dyn_cast<SCEVUnknown>(S))
     if (auto *I = dyn_cast<Instruction>(U->getValue()))
       return I;
-  // All SCEVs are bound by the entry to F
-  return &*F.getEntryBlock().begin();
+  return nullptr;
 }
 
 const Instruction *
 ScalarEvolution::getDefiningScopeBound(ArrayRef<const SCEV *> Ops) {
-  const Instruction *Bound = &*F.getEntryBlock().begin();
-  for (auto *S : Ops) {
-    auto *DefI = getDefiningScopeBound(S);
-    if (DT.dominates(Bound, DefI))
-      Bound = DefI;
-  }
-  return Bound;
+  const Instruction *Bound = nullptr;
+  for (auto *S : Ops)
+    if (auto *DefI = getNonTrivialDefiningScopeBound(S))
+      if (!Bound || DT.dominates(Bound, DefI))
+        Bound = DefI;
+  return Bound ? Bound : &*F.getEntryBlock().begin();
 }