From: Dan Gohman <gohman@apple.com>
Date: Mon, 13 Jul 2009 20:55:53 +0000 (+0000)
Subject: Move the memoization check for SCEVSignExtendExpr and
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=69fbc7f477c21ce1d8ae5a4aa8a701e47aa2d163;p=oota-llvm.git

Move the memoization check for SCEVSignExtendExpr and
SCEVZeroExtendExpr ahead of the most expensive analysis. This
speeds up analysis and helps avoid pathologically bad behavior
on the testcase in PR4534.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@75496 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Analysis/ScalarEvolution.cpp b/lib/Analysis/ScalarEvolution.cpp
index 815a6f21cd2..6a028c19faf 100644
--- a/lib/Analysis/ScalarEvolution.cpp
+++ b/lib/Analysis/ScalarEvolution.cpp
@@ -772,6 +772,15 @@ const SCEV *ScalarEvolution::getZeroExtendExpr(const SCEV *Op,
   if (const SCEVZeroExtendExpr *SZ = dyn_cast<SCEVZeroExtendExpr>(Op))
     return getZeroExtendExpr(SZ->getOperand(), Ty);
 
+  // Before doing any expensive analysis, check to see if we've already
+  // computed a SCEV for this Op and Ty.
+  FoldingSetNodeID ID;
+  ID.AddInteger(scZeroExtend);
+  ID.AddPointer(Op);
+  ID.AddPointer(Ty);
+  void *IP = 0;
+  if (const SCEV *S = UniqueSCEVs.FindNodeOrInsertPos(ID, IP)) return S;
+
   // If the input value is a chrec scev, and we can prove that the value
   // did not overflow the old, smaller, value, we can zero extend all of the
   // operands (often constants).  This allows analysis of something like
@@ -836,11 +845,8 @@ const SCEV *ScalarEvolution::getZeroExtendExpr(const SCEV *Op,
       }
     }
 
-  FoldingSetNodeID ID;
-  ID.AddInteger(scZeroExtend);
-  ID.AddPointer(Op);
-  ID.AddPointer(Ty);
-  void *IP = 0;
+  // The cast wasn't folded; create an explicit cast node.
+  // Recompute the insert position, as it may have been invalidated.
   if (const SCEV *S = UniqueSCEVs.FindNodeOrInsertPos(ID, IP)) return S;
   SCEV *S = SCEVAllocator.Allocate<SCEVZeroExtendExpr>();
   new (S) SCEVZeroExtendExpr(ID, Op, Ty);
@@ -868,6 +874,15 @@ const SCEV *ScalarEvolution::getSignExtendExpr(const SCEV *Op,
   if (const SCEVSignExtendExpr *SS = dyn_cast<SCEVSignExtendExpr>(Op))
     return getSignExtendExpr(SS->getOperand(), Ty);
 
+  // Before doing any expensive analysis, check to see if we've already
+  // computed a SCEV for this Op and Ty.
+  FoldingSetNodeID ID;
+  ID.AddInteger(scSignExtend);
+  ID.AddPointer(Op);
+  ID.AddPointer(Ty);
+  void *IP = 0;
+  if (const SCEV *S = UniqueSCEVs.FindNodeOrInsertPos(ID, IP)) return S;
+
   // If the input value is a chrec scev, and we can prove that the value
   // did not overflow the old, smaller, value, we can sign extend all of the
   // operands (often constants).  This allows analysis of something like
@@ -916,11 +931,8 @@ const SCEV *ScalarEvolution::getSignExtendExpr(const SCEV *Op,
       }
     }
 
-  FoldingSetNodeID ID;
-  ID.AddInteger(scSignExtend);
-  ID.AddPointer(Op);
-  ID.AddPointer(Ty);
-  void *IP = 0;
+  // The cast wasn't folded; create an explicit cast node.
+  // Recompute the insert position, as it may have been invalidated.
   if (const SCEV *S = UniqueSCEVs.FindNodeOrInsertPos(ID, IP)) return S;
   SCEV *S = SCEVAllocator.Allocate<SCEVSignExtendExpr>();
   new (S) SCEVSignExtendExpr(ID, Op, Ty);