From: Sanjoy Das <sanjoy@playingwithpointers.com>
Date: Fri, 14 Apr 2017 17:42:08 +0000 (+0000)
Subject: Make SCEVRewriteVisitor smarter about when it trys to create SCEVs
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=e4f44dfa7398c7669169973c1509659c5af60108;p=llvm

Make SCEVRewriteVisitor smarter about when it trys to create SCEVs

This change really saves just one foldingset lookup, but makes
SCEVRewriteVisitor "feature compatible" with the handwritten logic in
ScalarEvolutionNormalization, so that I can change
ScalarEvolutionNormalization to use SCEVRewriteVisitor in a next step.

This is a non-functional change, but _may_ improve performance in some
pathological cases, but that's unlikely.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@300348 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/include/llvm/Analysis/ScalarEvolutionExpressions.h b/include/llvm/Analysis/ScalarEvolutionExpressions.h
index fdcd8be00dd..1cee5d0b9e9 100644
--- a/include/llvm/Analysis/ScalarEvolutionExpressions.h
+++ b/include/llvm/Analysis/ScalarEvolutionExpressions.h
@@ -595,58 +595,82 @@ namespace llvm {
 
     const SCEV *visitTruncateExpr(const SCEVTruncateExpr *Expr) {
       const SCEV *Operand = ((SC*)this)->visit(Expr->getOperand());
-      return SE.getTruncateExpr(Operand, Expr->getType());
+      return Operand == Expr->getOperand()
+                 ? Expr
+                 : SE.getTruncateExpr(Operand, Expr->getType());
     }
 
     const SCEV *visitZeroExtendExpr(const SCEVZeroExtendExpr *Expr) {
       const SCEV *Operand = ((SC*)this)->visit(Expr->getOperand());
-      return SE.getZeroExtendExpr(Operand, Expr->getType());
+      return Operand == Expr->getOperand()
+                 ? Expr
+                 : SE.getZeroExtendExpr(Operand, Expr->getType());
     }
 
     const SCEV *visitSignExtendExpr(const SCEVSignExtendExpr *Expr) {
       const SCEV *Operand = ((SC*)this)->visit(Expr->getOperand());
-      return SE.getSignExtendExpr(Operand, Expr->getType());
+      return Operand == Expr->getOperand()
+                 ? Expr
+                 : SE.getSignExtendExpr(Operand, Expr->getType());
     }
 
     const SCEV *visitAddExpr(const SCEVAddExpr *Expr) {
       SmallVector<const SCEV *, 2> Operands;
-      for (int i = 0, e = Expr->getNumOperands(); i < e; ++i)
+      bool Changed = false;
+      for (int i = 0, e = Expr->getNumOperands(); i < e; ++i) {
         Operands.push_back(((SC*)this)->visit(Expr->getOperand(i)));
-      return SE.getAddExpr(Operands);
+        Changed |= Expr->getOperand(i) != Operands.back();
+      }
+      return !Changed ? Expr : SE.getAddExpr(Operands);
     }
 
     const SCEV *visitMulExpr(const SCEVMulExpr *Expr) {
       SmallVector<const SCEV *, 2> Operands;
-      for (int i = 0, e = Expr->getNumOperands(); i < e; ++i)
+      bool Changed = false;
+      for (int i = 0, e = Expr->getNumOperands(); i < e; ++i) {
         Operands.push_back(((SC*)this)->visit(Expr->getOperand(i)));
-      return SE.getMulExpr(Operands);
+        Changed |= Expr->getOperand(i) != Operands.back();
+      }
+      return !Changed ? Expr : SE.getMulExpr(Operands);
     }
 
     const SCEV *visitUDivExpr(const SCEVUDivExpr *Expr) {
-      return SE.getUDivExpr(((SC*)this)->visit(Expr->getLHS()),
-                            ((SC*)this)->visit(Expr->getRHS()));
+      auto *LHS = ((SC *)this)->visit(Expr->getLHS());
+      auto *RHS = ((SC *)this)->visit(Expr->getRHS());
+      bool Changed = LHS != Expr->getLHS() || RHS != Expr->getRHS();
+      return !Changed ? Expr : SE.getUDivExpr(LHS, RHS);
     }
 
     const SCEV *visitAddRecExpr(const SCEVAddRecExpr *Expr) {
       SmallVector<const SCEV *, 2> Operands;
-      for (int i = 0, e = Expr->getNumOperands(); i < e; ++i)
+      bool Changed = false;
+      for (int i = 0, e = Expr->getNumOperands(); i < e; ++i) {
         Operands.push_back(((SC*)this)->visit(Expr->getOperand(i)));
-      return SE.getAddRecExpr(Operands, Expr->getLoop(),
-                              Expr->getNoWrapFlags());
+        Changed |= Expr->getOperand(i) != Operands.back();
+      }
+      return !Changed ? Expr
+                      : SE.getAddRecExpr(Operands, Expr->getLoop(),
+                                         Expr->getNoWrapFlags());
     }
 
     const SCEV *visitSMaxExpr(const SCEVSMaxExpr *Expr) {
       SmallVector<const SCEV *, 2> Operands;
-      for (int i = 0, e = Expr->getNumOperands(); i < e; ++i)
-        Operands.push_back(((SC*)this)->visit(Expr->getOperand(i)));
-      return SE.getSMaxExpr(Operands);
+      bool Changed = false;
+      for (int i = 0, e = Expr->getNumOperands(); i < e; ++i) {
+        Operands.push_back(((SC *)this)->visit(Expr->getOperand(i)));
+        Changed |= Expr->getOperand(i) != Operands.back();
+      }
+      return !Changed ? Expr : SE.getSMaxExpr(Operands);
     }
 
     const SCEV *visitUMaxExpr(const SCEVUMaxExpr *Expr) {
       SmallVector<const SCEV *, 2> Operands;
-      for (int i = 0, e = Expr->getNumOperands(); i < e; ++i)
+      bool Changed = false;
+      for (int i = 0, e = Expr->getNumOperands(); i < e; ++i) {
         Operands.push_back(((SC*)this)->visit(Expr->getOperand(i)));
-      return SE.getUMaxExpr(Operands);
+        Changed |= Expr->getOperand(i) != Operands.back();
+      }
+      return !Changed ? Expr : SE.getUMaxExpr(Operands);
     }
 
     const SCEV *visitUnknown(const SCEVUnknown *Expr) {