[Power9] Add __float128 support in the backend for bitcast to a i128

Add support to allow bit-casting from f128 to i128 and then
extracting 64 bits from the result.

Differential Revision: https://reviews.llvm.org/D49507

llvm-svn: 345053

1 files changed, 58 insertions, 0 deletions

diff --git a/llvm/lib/Target/PowerPC/PPCISelLowering.cpp b/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
index 1fd5018d05c..ca60f318278 100644
--- a/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
+++ b/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
@@ -1070,6 +1070,8 @@ PPCTargetLowering::PPCTargetLowering(const PPCTargetMachine &TM,
   setTargetDAGCombine(ISD::ZERO_EXTEND);
   setTargetDAGCombine(ISD::ANY_EXTEND);
 
+  setTargetDAGCombine(ISD::TRUNCATE);
+
   if (Subtarget.useCRBits()) {
     setTargetDAGCombine(ISD::TRUNCATE);
     setTargetDAGCombine(ISD::SETCC);
@@ -9634,6 +9636,9 @@ void PPCTargetLowering::ReplaceNodeResults(SDNode *N,
       return;
     Results.push_back(LowerFP_TO_INT(SDValue(N, 0), DAG, dl));
     return;
+  case ISD::BITCAST:
+    // Don't handle bitcast here.
+    return;
   }
 }
 
@@ -12479,6 +12484,7 @@ SDValue PPCTargetLowering::PerformDAGCombine(SDNode *N,
   case ISD::ANY_EXTEND:
     return DAGCombineExtBoolTrunc(N, DCI);
   case ISD::TRUNCATE:
+    return combineTRUNCATE(N, DCI);
   case ISD::SETCC:
   case ISD::SELECT_CC:
     return DAGCombineTruncBoolExt(N, DCI);
@@ -14253,6 +14259,58 @@ SDValue PPCTargetLowering::combineADD(SDNode *N, DAGCombinerInfo &DCI) const {
   return SDValue();
 }
 
+// Detect TRUNCATE operations on bitcasts of float128 values.
+// What we are looking for here is the situtation where we extract a subset
+// of bits from a 128 bit float.
+// This can be of two forms:
+// 1) BITCAST of f128 feeding TRUNCATE
+// 2) BITCAST of f128 feeding SRL (a shift) feeding TRUNCATE
+// The reason this is required is because we do not have a legal i128 type
+// and so we want to prevent having to store the f128 and then reload part
+// of it.
+SDValue PPCTargetLowering::combineTRUNCATE(SDNode *N,
+                                           DAGCombinerInfo &DCI) const {
+  // If we are using CRBits then try that first.
+  if (Subtarget.useCRBits()) {
+    // Check if CRBits did anything and return that if it did.
+    if (SDValue CRTruncValue = DAGCombineTruncBoolExt(N, DCI))
+      return CRTruncValue;
+  }
+
+  SDLoc dl(N);
+  SDValue Op0 = N->getOperand(0);
+
+  // Looking for a truncate of i128 to i64.
+  if (Op0.getValueType() != MVT::i128 || N->getValueType(0) != MVT::i64)
+    return SDValue();
+
+  int EltToExtract = DCI.DAG.getDataLayout().isBigEndian() ? 1 : 0;
+
+  // SRL feeding TRUNCATE.
+  if (Op0.getOpcode() == ISD::SRL) {
+    ConstantSDNode *ConstNode = dyn_cast<ConstantSDNode>(Op0.getOperand(1));
+    // The right shift has to be by 64 bits.
+    if (!ConstNode || ConstNode->getZExtValue() != 64)
+      return SDValue();
+
+    // Switch the element number to extract.
+    EltToExtract = EltToExtract ? 0 : 1;
+    // Update Op0 past the SRL.
+    Op0 = Op0.getOperand(0);
+  }
+
+  // BITCAST feeding a TRUNCATE possibly via SRL.
+  if (Op0.getOpcode() == ISD::BITCAST &&
+      Op0.getValueType() == MVT::i128 &&
+      Op0.getOperand(0).getValueType() == MVT::f128) {
+    SDValue Bitcast = DCI.DAG.getBitcast(MVT::v2i64, Op0.getOperand(0));
+    return DCI.DAG.getNode(
+        ISD::EXTRACT_VECTOR_ELT, dl, MVT::i64, Bitcast,
+        DCI.DAG.getTargetConstant(EltToExtract, dl, MVT::i32));
+  }
+  return SDValue();
+}
+
 bool PPCTargetLowering::mayBeEmittedAsTailCall(const CallInst *CI) const {
   // Only duplicate to increase tail-calls for the 64bit SysV ABIs.
   if (!Subtarget.isSVR4ABI() || !Subtarget.isPPC64())