Rename ValueRequiresCast to ShouldOptimizeCast, to better reflect

what it does.  Enhance it to return false to optimizing vector
sign extensions from vector comparisions, which is the idiom used
to get a splatted vector for a vector comparison.

Doing this breaks vector-casts.ll, add some compensating 
transformations to handle the important case they cover without
depending on this canonicalization.

This fixes rdar://7434900 a serious pessimization of vector compares.

llvm-svn: 95855

3 files changed, 97 insertions, 55 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombine.h b/llvm/lib/Transforms/InstCombine/InstCombine.h
index 536790004e8..09accb6b857 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombine.h
+++ b/llvm/lib/Transforms/InstCombine/InstCombine.h
@@ -199,11 +199,12 @@ private:
                                   SmallVectorImpl<Value*> &NewIndices);
   Instruction *FoldOpIntoSelect(Instruction &Op, SelectInst *SI);
                                  
-  /// ValueRequiresCast - Return true if the cast from "V to Ty" actually
-  /// results in any code being generated.  It does not require codegen if V is
-  /// simple enough or if the cast can be folded into other casts.
-  bool ValueRequiresCast(Instruction::CastOps opcode,const Value *V,
-                         const Type *Ty);
+  /// ShouldOptimizeCast - Return true if the cast from "V to Ty" actually
+  /// results in any code being generated and is interesting to optimize out. If
+  /// the cast can be eliminated by some other simple transformation, we prefer
+  /// to do the simplification first.
+  bool ShouldOptimizeCast(Instruction::CastOps opcode,const Value *V,
+                          const Type *Ty);
 
   Instruction *visitCallSite(CallSite CS);
   bool transformConstExprCastCall(CallSite CS);
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
index 28fd70ef69f..515753fae49 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
@@ -932,24 +932,49 @@ Instruction *InstCombiner::visitAnd(BinaryOperator &I) {
     if (ICmpInst *LHS = dyn_cast<ICmpInst>(Op0))
       if (Instruction *Res = FoldAndOfICmps(I, LHS, RHS))
         return Res;
-
+  
+  // If and'ing two fcmp, try combine them into one.
+  if (FCmpInst *LHS = dyn_cast<FCmpInst>(I.getOperand(0)))
+    if (FCmpInst *RHS = dyn_cast<FCmpInst>(I.getOperand(1)))
+      if (Instruction *Res = FoldAndOfFCmps(I, LHS, RHS))
+        return Res;
+  
+  
   // fold (and (cast A), (cast B)) -> (cast (and A, B))
   if (CastInst *Op0C = dyn_cast<CastInst>(Op0))
-    if (CastInst *Op1C = dyn_cast<CastInst>(Op1))
-      if (Op0C->getOpcode() == Op1C->getOpcode()) { // same cast kind ?
-        const Type *SrcTy = Op0C->getOperand(0)->getType();
-        if (SrcTy == Op1C->getOperand(0)->getType() &&
-            SrcTy->isIntOrIntVector() &&
-            // Only do this if the casts both really cause code to be generated.
-            ValueRequiresCast(Op0C->getOpcode(), Op0C->getOperand(0),
-                              I.getType()) &&
-            ValueRequiresCast(Op1C->getOpcode(), Op1C->getOperand(0), 
-                              I.getType())) {
-          Value *NewOp = Builder->CreateAnd(Op0C->getOperand(0),
-                                            Op1C->getOperand(0), I.getName());
+    if (CastInst *Op1C = dyn_cast<CastInst>(Op1)) {
+      const Type *SrcTy = Op0C->getOperand(0)->getType();
+      if (Op0C->getOpcode() == Op1C->getOpcode() && // same cast kind ?
+          SrcTy == Op1C->getOperand(0)->getType() &&
+          SrcTy->isIntOrIntVector()) {
+        Value *Op0COp = Op0C->getOperand(0), *Op1COp = Op1C->getOperand(0);
+        
+        // Only do this if the casts both really cause code to be generated.
+        if (ShouldOptimizeCast(Op0C->getOpcode(), Op0COp, I.getType()) &&
+            ShouldOptimizeCast(Op1C->getOpcode(), Op1COp, I.getType())) {
+          Value *NewOp = Builder->CreateAnd(Op0COp, Op1COp, I.getName());
           return CastInst::Create(Op0C->getOpcode(), NewOp, I.getType());
         }
+        
+        // If this is and(cast(icmp), cast(icmp)), try to fold this even if the
+        // cast is otherwise not optimizable.  This happens for vector sexts.
+        if (ICmpInst *RHS = dyn_cast<ICmpInst>(Op1COp))
+          if (ICmpInst *LHS = dyn_cast<ICmpInst>(Op0COp))
+            if (Instruction *Res = FoldAndOfICmps(I, LHS, RHS)) {
+              InsertNewInstBefore(Res, I);
+              return CastInst::Create(Op0C->getOpcode(), Res, I.getType());
+            }
+        
+        // If this is and(cast(fcmp), cast(fcmp)), try to fold this even if the
+        // cast is otherwise not optimizable.  This happens for vector sexts.
+        if (FCmpInst *RHS = dyn_cast<FCmpInst>(Op1COp))
+          if (FCmpInst *LHS = dyn_cast<FCmpInst>(Op0COp))
+            if (Instruction *Res = FoldAndOfFCmps(I, LHS, RHS)) {
+              InsertNewInstBefore(Res, I);
+              return CastInst::Create(Op0C->getOpcode(), Res, I.getType());
+            }
       }
+    }
     
   // (X >> Z) & (Y >> Z)  -> (X&Y) >> Z  for all shifts.
   if (BinaryOperator *SI1 = dyn_cast<BinaryOperator>(Op1)) {
@@ -965,13 +990,6 @@ Instruction *InstCombiner::visitAnd(BinaryOperator &I) {
       }
   }
 
-  // If and'ing two fcmp, try combine them into one.
-  if (FCmpInst *LHS = dyn_cast<FCmpInst>(I.getOperand(0))) {
-    if (FCmpInst *RHS = dyn_cast<FCmpInst>(I.getOperand(1)))
-      if (Instruction *Res = FoldAndOfFCmps(I, LHS, RHS))
-        return Res;
-  }
-
   return Changed ? &I : 0;
 }
 
@@ -1669,37 +1687,51 @@ Instruction *InstCombiner::visitOr(BinaryOperator &I) {
       if (Instruction *Res = FoldOrOfICmps(I, LHS, RHS))
         return Res;
     
+  // (fcmp uno x, c) | (fcmp uno y, c)  -> (fcmp uno x, y)
+  if (FCmpInst *LHS = dyn_cast<FCmpInst>(I.getOperand(0)))
+    if (FCmpInst *RHS = dyn_cast<FCmpInst>(I.getOperand(1)))
+      if (Instruction *Res = FoldOrOfFCmps(I, LHS, RHS))
+        return Res;
+  
   // fold (or (cast A), (cast B)) -> (cast (or A, B))
   if (CastInst *Op0C = dyn_cast<CastInst>(Op0)) {
     if (CastInst *Op1C = dyn_cast<CastInst>(Op1))
       if (Op0C->getOpcode() == Op1C->getOpcode()) {// same cast kind ?
-        if (!isa<ICmpInst>(Op0C->getOperand(0)) ||
-            !isa<ICmpInst>(Op1C->getOperand(0))) {
-          const Type *SrcTy = Op0C->getOperand(0)->getType();
-          if (SrcTy == Op1C->getOperand(0)->getType() &&
-              SrcTy->isIntOrIntVector() &&
+        const Type *SrcTy = Op0C->getOperand(0)->getType();
+        if (SrcTy == Op1C->getOperand(0)->getType() &&
+            SrcTy->isIntOrIntVector()) {
+          Value *Op0COp = Op0C->getOperand(0), *Op1COp = Op1C->getOperand(0);
+
+          if ((!isa<ICmpInst>(Op0COp) || !isa<ICmpInst>(Op1COp)) &&
               // Only do this if the casts both really cause code to be
               // generated.
-              ValueRequiresCast(Op0C->getOpcode(), Op0C->getOperand(0), 
-                                I.getType()) &&
-              ValueRequiresCast(Op1C->getOpcode(), Op1C->getOperand(0), 
-                                I.getType())) {
-            Value *NewOp = Builder->CreateOr(Op0C->getOperand(0),
-                                             Op1C->getOperand(0), I.getName());
+              ShouldOptimizeCast(Op0C->getOpcode(), Op0COp, I.getType()) &&
+              ShouldOptimizeCast(Op1C->getOpcode(), Op1COp, I.getType())) {
+            Value *NewOp = Builder->CreateOr(Op0COp, Op1COp, I.getName());
             return CastInst::Create(Op0C->getOpcode(), NewOp, I.getType());
           }
+          
+          // If this is or(cast(icmp), cast(icmp)), try to fold this even if the
+          // cast is otherwise not optimizable.  This happens for vector sexts.
+          if (ICmpInst *RHS = dyn_cast<ICmpInst>(Op1COp))
+            if (ICmpInst *LHS = dyn_cast<ICmpInst>(Op0COp))
+              if (Instruction *Res = FoldOrOfICmps(I, LHS, RHS)) {
+                InsertNewInstBefore(Res, I);
+                return CastInst::Create(Op0C->getOpcode(), Res, I.getType());
+              }
+          
+          // If this is or(cast(fcmp), cast(fcmp)), try to fold this even if the
+          // cast is otherwise not optimizable.  This happens for vector sexts.
+          if (FCmpInst *RHS = dyn_cast<FCmpInst>(Op1COp))
+            if (FCmpInst *LHS = dyn_cast<FCmpInst>(Op0COp))
+              if (Instruction *Res = FoldOrOfFCmps(I, LHS, RHS)) {
+                InsertNewInstBefore(Res, I);
+                return CastInst::Create(Op0C->getOpcode(), Res, I.getType());
+              }
         }
       }
   }
   
-    
-  // (fcmp uno x, c) | (fcmp uno y, c)  -> (fcmp uno x, y)
-  if (FCmpInst *LHS = dyn_cast<FCmpInst>(I.getOperand(0))) {
-    if (FCmpInst *RHS = dyn_cast<FCmpInst>(I.getOperand(1)))
-      if (Instruction *Res = FoldOrOfFCmps(I, LHS, RHS))
-        return Res;
-  }
-
   return Changed ? &I : 0;
 }
 
@@ -1986,10 +2018,10 @@ Instruction *InstCombiner::visitXor(BinaryOperator &I) {
         const Type *SrcTy = Op0C->getOperand(0)->getType();
         if (SrcTy == Op1C->getOperand(0)->getType() && SrcTy->isInteger() &&
             // Only do this if the casts both really cause code to be generated.
-            ValueRequiresCast(Op0C->getOpcode(), Op0C->getOperand(0), 
-                              I.getType()) &&
-            ValueRequiresCast(Op1C->getOpcode(), Op1C->getOperand(0), 
-                              I.getType())) {
+            ShouldOptimizeCast(Op0C->getOpcode(), Op0C->getOperand(0), 
+                               I.getType()) &&
+            ShouldOptimizeCast(Op1C->getOpcode(), Op1C->getOperand(0), 
+                               I.getType())) {
           Value *NewOp = Builder->CreateXor(Op0C->getOperand(0),
                                             Op1C->getOperand(0), I.getName());
           return CastInst::Create(Op0C->getOpcode(), NewOp, I.getType());
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
index 09cd21f1443..68e17e59f6a 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
@@ -255,17 +255,26 @@ isEliminableCastPair(
   return Instruction::CastOps(Res);
 }
 
-/// ValueRequiresCast - Return true if the cast from "V to Ty" actually results
-/// in any code being generated.  It does not require codegen if V is simple
-/// enough or if the cast can be folded into other casts.
-bool InstCombiner::ValueRequiresCast(Instruction::CastOps opcode,const Value *V,
-                                     const Type *Ty) {
+/// ShouldOptimizeCast - Return true if the cast from "V to Ty" actually
+/// results in any code being generated and is interesting to optimize out. If
+/// the cast can be eliminated by some other simple transformation, we prefer
+/// to do the simplification first.
+bool InstCombiner::ShouldOptimizeCast(Instruction::CastOps opc, const Value *V,
+                                      const Type *Ty) {
+  // Noop casts and casts of constants should be eliminated trivially.
   if (V->getType() == Ty || isa<Constant>(V)) return false;
   
-  // If this is another cast that can be eliminated, it isn't codegen either.
+  // If this is another cast that can be eliminated, we prefer to have it
+  // eliminated.
   if (const CastInst *CI = dyn_cast<CastInst>(V))
-    if (isEliminableCastPair(CI, opcode, Ty, TD))
+    if (isEliminableCastPair(CI, opc, Ty, TD))
       return false;
+  
+  // If this is a vector sext from a compare, then we don't want to break the
+  // idiom where each element of the extended vector is either zero or all ones.
+  if (opc == Instruction::SExt && isa<CmpInst>(V) && isa<VectorType>(Ty))
+    return false;
+  
   return true;
 }