Add predicates for checking whether targets have free FNEG and FABS operations, and prevent the DAGCombiner from turning them into bitwise operations if they do.

llvm-svn: 153901

2 files changed, 17 insertions, 3 deletions

diff --git a/llvm/include/llvm/Target/TargetLowering.h b/llvm/include/llvm/Target/TargetLowering.h
index 08420ef70b9..153138f08af 100644
--- a/llvm/include/llvm/Target/TargetLowering.h
+++ b/llvm/include/llvm/Target/TargetLowering.h
@@ -1600,6 +1600,18 @@ public:
     return false;
   }
 
+  /// isFNegFree - Return true if an fneg operation is free to the point where
+  /// it is never worthwhile to replace it with a bitwise operation.
+  virtual bool isFNegFree(EVT) const {
+    return false;
+  }
+
+  /// isFAbsFree - Return true if an fneg operation is free to the point where
+  /// it is never worthwhile to replace it with a bitwise operation.
+  virtual bool isFAbsFree(EVT) const {
+    return false;
+  }
+
   /// isNarrowingProfitable - Return true if it's profitable to narrow
   /// operations of type VT1 to VT2. e.g. on x86, it's profitable to narrow
   /// from i32 to i8 but not from i32 to i16.
diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 08946070b44..a71cf82cd58 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -5342,7 +5342,8 @@ SDValue DAGCombiner::visitBITCAST(SDNode *N) {
   // fold (bitconvert (fneg x)) -> (xor (bitconvert x), signbit)
   // fold (bitconvert (fabs x)) -> (and (bitconvert x), (not signbit))
   // This often reduces constant pool loads.
-  if ((N0.getOpcode() == ISD::FNEG || N0.getOpcode() == ISD::FABS) &&
+  if (((N0.getOpcode() == ISD::FNEG && !TLI.isFNegFree(VT)) ||
+       (N0.getOpcode() == ISD::FABS && !TLI.isFAbsFree(VT))) &&
       N0.getNode()->hasOneUse() && VT.isInteger() && !VT.isVector()) {
     SDValue NewConv = DAG.getNode(ISD::BITCAST, N0.getDebugLoc(), VT,
                                   N0.getOperand(0));
@@ -5993,7 +5994,7 @@ SDValue DAGCombiner::visitFNEG(SDNode *N) {
 
   // Transform fneg(bitconvert(x)) -> bitconvert(x^sign) to avoid loading
   // constant pool values.
-  if (N0.getOpcode() == ISD::BITCAST &&
+  if (!TLI.isFNegFree(VT) && N0.getOpcode() == ISD::BITCAST &&
       !VT.isVector() &&
       N0.getNode()->hasOneUse() &&
       N0.getOperand(0).getValueType().isInteger()) {
@@ -6029,7 +6030,8 @@ SDValue DAGCombiner::visitFABS(SDNode *N) {
 
   // Transform fabs(bitconvert(x)) -> bitconvert(x&~sign) to avoid loading
   // constant pool values.
-  if (N0.getOpcode() == ISD::BITCAST && N0.getNode()->hasOneUse() &&
+  if (!TLI.isFAbsFree(VT) && 
+      N0.getOpcode() == ISD::BITCAST && N0.getNode()->hasOneUse() &&
       N0.getOperand(0).getValueType().isInteger() &&
       !N0.getOperand(0).getValueType().isVector()) {
     SDValue Int = N0.getOperand(0);