From: Evan Cheng <evan.cheng@apple.com>
Date: Tue, 18 Jul 2006 19:07:58 +0000 (+0000)
Subject: Only reuse a previous IV if it would not require a type conversion.
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=31e773147bf13cb11c2bf343db5706fe3e2923d7;p=oota-llvm.git

Only reuse a previous IV if it would not require a type conversion.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@29186 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Transforms/Scalar/LoopStrengthReduce.cpp b/lib/Transforms/Scalar/LoopStrengthReduce.cpp
index ec15b646c73..bcdf6dabe54 100644
--- a/lib/Transforms/Scalar/LoopStrengthReduce.cpp
+++ b/lib/Transforms/Scalar/LoopStrengthReduce.cpp
@@ -187,7 +187,7 @@ private:
 
     void OptimizeIndvars(Loop *L);
 
-    unsigned CheckForIVReuse(const SCEVHandle &Stride, IVExpr &IV);
+    unsigned CheckForIVReuse(const SCEVHandle&, IVExpr&, const Type*);
 
     void StrengthReduceStridedIVUsers(const SCEVHandle &Stride,
                                       IVUsersOfOneStride &Uses,
@@ -872,7 +872,7 @@ static bool isZero(SCEVHandle &V) {
 /// mode scale component. This allows the users of this stride to be rewritten
 /// as prev iv * factor. It returns 0 if no reuse is possible.
 unsigned LoopStrengthReduce::CheckForIVReuse(const SCEVHandle &Stride,
-                                             IVExpr &IV) {
+                                             IVExpr &IV, const Type *Ty) {
   if (!TLI) return 0;
 
   if (SCEVConstant *SC = dyn_cast<SCEVConstant>(Stride)) {
@@ -892,7 +892,9 @@ unsigned LoopStrengthReduce::CheckForIVReuse(const SCEVHandle &Stride,
       for (std::vector<IVExpr>::iterator II = SI->second.IVs.begin(),
              IE = SI->second.IVs.end(); II != IE; ++II)
         // FIXME: Only handle base == 0 for now.
-        if (isZero(II->Base)) {
+        // Only reuse previous IV if it would not require a type conversion.
+        if (isZero(II->Base) &&
+            II->Base->getType()->isLosslesslyConvertibleTo(Ty)) {
           IV = *II;
           return Scale;
         }
@@ -929,13 +931,24 @@ void LoopStrengthReduce::StrengthReduceStridedIVUsers(const SCEVHandle &Stride,
            "Base value is not loop invariant!");
   }
 
+  // We now have a whole bunch of uses of like-strided induction variables, but
+  // they might all have different bases.  We want to emit one PHI node for this
+  // stride which we fold as many common expressions (between the IVs) into as
+  // possible.  Start by identifying the common expressions in the base values 
+  // for the strides (e.g. if we have "A+C+B" and "A+B+D" as our bases, find
+  // "A+B"), emit it to the preheader, then remove the expression from the
+  // UsersToProcess base values.
+  SCEVHandle CommonExprs =
+    RemoveCommonExpressionsFromUseBases(UsersToProcess);
+  
   // Check if it is possible to reuse a IV with stride that is factor of this
   // stride. And the multiple is a number that can be encoded in the scale
   // field of the target addressing mode.
   PHINode *NewPHI = NULL;
   Value   *IncV   = NULL;
   IVExpr   ReuseIV;
-  unsigned RewriteFactor = CheckForIVReuse(Stride, ReuseIV);
+  unsigned RewriteFactor = CheckForIVReuse(Stride, ReuseIV,
+                                           CommonExprs->getType());
   if (RewriteFactor != 0) {
     DEBUG(std::cerr << "BASED ON IV of STRIDE " << *ReuseIV.Stride
           << " and BASE " << *ReuseIV.Base << " :\n");
@@ -943,16 +956,6 @@ void LoopStrengthReduce::StrengthReduceStridedIVUsers(const SCEVHandle &Stride,
     IncV   = ReuseIV.IncV;
   }
 
-  // We now have a whole bunch of uses of like-strided induction variables, but
-  // they might all have different bases.  We want to emit one PHI node for this
-  // stride which we fold as many common expressions (between the IVs) into as
-  // possible.  Start by identifying the common expressions in the base values 
-  // for the strides (e.g. if we have "A+C+B" and "A+B+D" as our bases, find
-  // "A+B"), emit it to the preheader, then remove the expression from the
-  // UsersToProcess base values.
-  SCEVHandle CommonExprs =
-    RemoveCommonExpressionsFromUseBases(UsersToProcess);
-  
   // Next, figure out what we can represent in the immediate fields of
   // instructions.  If we can represent anything there, move it to the imm
   // fields of the BasedUsers.  We do this so that it increases the commonality