ARM: implement some simple f64 materializations.

Previously we used a const-pool load for virtually all 64-bit floating values.
Actually, we can get quite a few common values (including 0.0, 1.0) via "vmov"
instructions of one stripe or another.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@188773 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 40 insertions, 10 deletions

diff --git a/lib/Target/ARM/ARMISelLowering.cpp b/lib/Target/ARM/ARMISelLowering.cpp
index caec11e..f22c5b9 100644
--- a/lib/Target/ARM/ARMISelLowering.cpp
+++ b/lib/Target/ARM/ARMISelLowering.cpp
@@ -452,6 +452,7 @@ ARMTargetLowering::ARMTargetLowering(TargetMachine &TM)
   }
 
   setOperationAction(ISD::ConstantFP, MVT::f32, Custom);
+  setOperationAction(ISD::ConstantFP, MVT::f64, Custom);
 
   if (Subtarget->hasNEON()) {
     addDRTypeForNEON(MVT::v2f32);
@@ -4271,17 +4272,25 @@ static SDValue isNEONModifiedImm(uint64_t SplatBits, uint64_t SplatUndef,
 
 SDValue ARMTargetLowering::LowerConstantFP(SDValue Op, SelectionDAG &DAG,
                                            const ARMSubtarget *ST) const {
-  if (!ST->useNEONForSinglePrecisionFP() || !ST->hasVFP3() || ST->hasD16())
+  if (!ST->hasVFP3())
     return SDValue();
 
+  bool IsDouble = Op.getValueType() == MVT::f64;
   ConstantFPSDNode *CFP = cast<ConstantFPSDNode>(Op);
-  assert(Op.getValueType() == MVT::f32 &&
-         "ConstantFP custom lowering should only occur for f32.");
 
   // Try splatting with a VMOV.f32...
   APFloat FPVal = CFP->getValueAPF();
-  int ImmVal = ARM_AM::getFP32Imm(FPVal);
+  int ImmVal = IsDouble ? ARM_AM::getFP64Imm(FPVal) : ARM_AM::getFP32Imm(FPVal);
+
   if (ImmVal != -1) {
+    if (IsDouble || !ST->useNEONForSinglePrecisionFP()) {
+      // We have code in place to select a valid ConstantFP already, no need to
+      // do any mangling.
+      return Op;
+    }
+
+    // It's a float and we are trying to use NEON operations where
+    // possible. Lower it to a splat followed by an extract.
     SDLoc DL(Op);
     SDValue NewVal = DAG.getTargetConstant(ImmVal, MVT::i32);
     SDValue VecConstant = DAG.getNode(ARMISD::VMOVFPIMM, DL, MVT::v2f32,
@@ -4290,15 +4299,31 @@ SDValue ARMTargetLowering::LowerConstantFP(SDValue Op, SelectionDAG &DAG,
                        DAG.getConstant(0, MVT::i32));
   }
 
-  // If that fails, try a VMOV.i32
+  // The rest of our options are NEON only, make sure that's allowed before
+  // proceeding..
+  if (!ST->hasNEON() || (!IsDouble && !ST->useNEONForSinglePrecisionFP()))
+    return SDValue();
+
   EVT VMovVT;
-  unsigned iVal = FPVal.bitcastToAPInt().getZExtValue();
-  SDValue NewVal = isNEONModifiedImm(iVal, 0, 32, DAG, VMovVT, false,
-                                     VMOVModImm);
+  uint64_t iVal = FPVal.bitcastToAPInt().getZExtValue();
+
+  // It wouldn't really be worth bothering for doubles except for one very
+  // important value, which does happen to match: 0.0. So make sure we don't do
+  // anything stupid.
+  if (IsDouble && (iVal & 0xffffffff) != (iVal >> 32))
+    return SDValue();
+
+  // Try a VMOV.i32 (FIXME: i8, i16, or i64 could work too).
+  SDValue NewVal = isNEONModifiedImm(iVal & 0xffffffffU, 0, 32, DAG, VMovVT,
+                                     false, VMOVModImm);
   if (NewVal != SDValue()) {
     SDLoc DL(Op);
     SDValue VecConstant = DAG.getNode(ARMISD::VMOVIMM, DL, VMovVT,
                                       NewVal);
+    if (IsDouble)
+      return DAG.getNode(ISD::BITCAST, DL, MVT::f64, VecConstant);
+
+    // It's a float: cast and extract a vector element.
     SDValue VecFConstant = DAG.getNode(ISD::BITCAST, DL, MVT::v2f32,
                                        VecConstant);
     return DAG.getNode(ISD::EXTRACT_VECTOR_ELT, DL, MVT::f32, VecFConstant,
@@ -4306,11 +4331,16 @@ SDValue ARMTargetLowering::LowerConstantFP(SDValue Op, SelectionDAG &DAG,
   }
 
   // Finally, try a VMVN.i32
-  NewVal = isNEONModifiedImm(~iVal & 0xffffffff, 0, 32, DAG, VMovVT, false,
-                             VMVNModImm);
+  NewVal = isNEONModifiedImm(~iVal & 0xffffffffU, 0, 32, DAG, VMovVT,
+                             false, VMVNModImm);
   if (NewVal != SDValue()) {
     SDLoc DL(Op);
     SDValue VecConstant = DAG.getNode(ARMISD::VMVNIMM, DL, VMovVT, NewVal);
+
+    if (IsDouble)
+      return DAG.getNode(ISD::BITCAST, DL, MVT::f64, VecConstant);
+
+    // It's a float: cast and extract a vector element.
     SDValue VecFConstant = DAG.getNode(ISD::BITCAST, DL, MVT::v2f32,
                                        VecConstant);
     return DAG.getNode(ISD::EXTRACT_VECTOR_ELT, DL, MVT::f32, VecFConstant,