[llvm] Nvptx port LowerBITCAST to SelectionDAG (PR #120903)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-llvm-selectiondag

@llvm/pr-subscribers-backend-nvptx

Author: None (GrumpyPigSkin)

<details>
<summary>Changes</summary>

Addressing #<!-- -->116695: Ports Bitcast to SelectionDAG

---
Full diff: https://github.com/llvm/llvm-project/pull/120903.diff


5 Files Affected:

- (modified) llvm/lib/CodeGen/SelectionDAG/LegalizeIntegerTypes.cpp (+6-2) 
- (modified) llvm/lib/CodeGen/SelectionDAG/LegalizeTypes.cpp (+32) 
- (modified) llvm/lib/CodeGen/SelectionDAG/LegalizeTypes.h (+1) 
- (modified) llvm/lib/Target/NVPTX/NVPTXISelLowering.cpp (+1-25) 
- (modified) llvm/lib/Target/NVPTX/NVPTXISelLowering.h (-2) 


``````````diff
diff --git a/llvm/lib/CodeGen/SelectionDAG/LegalizeIntegerTypes.cpp b/llvm/lib/CodeGen/SelectionDAG/LegalizeIntegerTypes.cpp
index be7521f3416850..bcb59e3c2aef3e 100644
--- a/llvm/lib/CodeGen/SelectionDAG/LegalizeIntegerTypes.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/LegalizeIntegerTypes.cpp
@@ -2174,8 +2174,12 @@ SDValue DAGTypeLegalizer::PromoteIntOp_ATOMIC_STORE(AtomicSDNode *N) {
 }
 
 SDValue DAGTypeLegalizer::PromoteIntOp_BITCAST(SDNode *N) {
-  // This should only occur in unusual situations like bitcasting to an
-  // x86_fp80, so just turn it into a store+load
+  // Use the custom lowering.
+  if (const auto Res = LowerBitcast(N)) {
+    return Res;
+  }
+
+  // If it fails fall back to the default method
   return CreateStackStoreLoad(N->getOperand(0), N->getValueType(0));
 }
 
diff --git a/llvm/lib/CodeGen/SelectionDAG/LegalizeTypes.cpp b/llvm/lib/CodeGen/SelectionDAG/LegalizeTypes.cpp
index b6abad830c371e..4aecf667b2cee1 100644
--- a/llvm/lib/CodeGen/SelectionDAG/LegalizeTypes.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/LegalizeTypes.cpp
@@ -910,6 +910,38 @@ SDValue DAGTypeLegalizer::CreateStackStoreLoad(SDValue Op,
   return DAG.getLoad(DestVT, dl, Store, StackPtr, MachinePointerInfo(), Align);
 }
 
+static SDValue MaybeBitcast(SelectionDAG &DAG, SDLoc DL, EVT VT,
+                            SDValue Value) {
+  if (Value->getValueType(0) == VT)
+    return Value;
+  return DAG.getNode(ISD::BITCAST, DL, VT, Value);
+}
+
+SDValue DAGTypeLegalizer::LowerBitcast(SDNode *Node) const {
+  assert(Node->getOpcode() == ISD::BITCAST && "Unexpected opcode!");
+  // Handle bitcasting from v2i8 without hitting the default promotion
+  // strategy which goes through stack memory.
+  EVT FromVT = Node->getOperand(0)->getValueType(0);
+  if (FromVT != MVT::v2i8) {
+    return SDValue();
+  }
+
+  // Pack vector elements into i16 and bitcast to final type
+  SDLoc DL(Node);
+  SDValue Vec0 = DAG.getNode(ISD::EXTRACT_VECTOR_ELT, DL, MVT::i8,
+                             Node->getOperand(0), DAG.getIntPtrConstant(0, DL));
+  SDValue Vec1 = DAG.getNode(ISD::EXTRACT_VECTOR_ELT, DL, MVT::i8,
+                             Node->getOperand(0), DAG.getIntPtrConstant(1, DL));
+  SDValue Extend0 = DAG.getNode(ISD::ZERO_EXTEND, DL, MVT::i16, Vec0);
+  SDValue Extend1 = DAG.getNode(ISD::ZERO_EXTEND, DL, MVT::i16, Vec1);
+  SDValue Const8 = DAG.getConstant(8, DL, MVT::i16);
+  SDValue AsInt = DAG.getNode(
+      ISD::OR, DL, MVT::i16,
+      {Extend0, DAG.getNode(ISD::SHL, DL, MVT::i16, {Extend1, Const8})});
+  EVT ToVT = Node->getValueType(0);
+  return MaybeBitcast(DAG, DL, ToVT, AsInt);
+}
+
 /// Replace the node's results with custom code provided by the target and
 /// return "true", or do nothing and return "false".
 /// The last parameter is FALSE if we are dealing with a node with legal
diff --git a/llvm/lib/CodeGen/SelectionDAG/LegalizeTypes.h b/llvm/lib/CodeGen/SelectionDAG/LegalizeTypes.h
index 571a710cc92a34..30951112069ed5 100644
--- a/llvm/lib/CodeGen/SelectionDAG/LegalizeTypes.h
+++ b/llvm/lib/CodeGen/SelectionDAG/LegalizeTypes.h
@@ -216,6 +216,7 @@ class LLVM_LIBRARY_VISIBILITY DAGTypeLegalizer {
   SDValue BitConvertToInteger(SDValue Op);
   SDValue BitConvertVectorToIntegerVector(SDValue Op);
   SDValue CreateStackStoreLoad(SDValue Op, EVT DestVT);
+  SDValue LowerBitcast(SDNode *N) const;
   bool CustomLowerNode(SDNode *N, EVT VT, bool LegalizeResult);
   bool CustomWidenLowerNode(SDNode *N, EVT VT);
 
diff --git a/llvm/lib/Target/NVPTX/NVPTXISelLowering.cpp b/llvm/lib/Target/NVPTX/NVPTXISelLowering.cpp
index 5c1f717694a4c7..2eaeb624004730 100644
--- a/llvm/lib/Target/NVPTX/NVPTXISelLowering.cpp
+++ b/llvm/lib/Target/NVPTX/NVPTXISelLowering.cpp
@@ -2086,30 +2086,6 @@ NVPTXTargetLowering::LowerCONCAT_VECTORS(SDValue Op, SelectionDAG &DAG) const {
   return DAG.getBuildVector(Node->getValueType(0), dl, Ops);
 }
 
-SDValue NVPTXTargetLowering::LowerBITCAST(SDValue Op, SelectionDAG &DAG) const {
-  // Handle bitcasting from v2i8 without hitting the default promotion
-  // strategy which goes through stack memory.
-  EVT FromVT = Op->getOperand(0)->getValueType(0);
-  if (FromVT != MVT::v2i8) {
-    return Op;
-  }
-
-  // Pack vector elements into i16 and bitcast to final type
-  SDLoc DL(Op);
-  SDValue Vec0 = DAG.getNode(ISD::EXTRACT_VECTOR_ELT, DL, MVT::i8,
-                             Op->getOperand(0), DAG.getIntPtrConstant(0, DL));
-  SDValue Vec1 = DAG.getNode(ISD::EXTRACT_VECTOR_ELT, DL, MVT::i8,
-                             Op->getOperand(0), DAG.getIntPtrConstant(1, DL));
-  SDValue Extend0 = DAG.getNode(ISD::ZERO_EXTEND, DL, MVT::i16, Vec0);
-  SDValue Extend1 = DAG.getNode(ISD::ZERO_EXTEND, DL, MVT::i16, Vec1);
-  SDValue Const8 = DAG.getConstant(8, DL, MVT::i16);
-  SDValue AsInt = DAG.getNode(
-      ISD::OR, DL, MVT::i16,
-      {Extend0, DAG.getNode(ISD::SHL, DL, MVT::i16, {Extend1, Const8})});
-  EVT ToVT = Op->getValueType(0);
-  return MaybeBitcast(DAG, DL, ToVT, AsInt);
-}
-
 // We can init constant f16x2/v2i16/v4i8 with a single .b32 move.  Normally it
 // would get lowered as two constant loads and vector-packing move.
 // Instead we want just a constant move:
@@ -2619,7 +2595,7 @@ NVPTXTargetLowering::LowerOperation(SDValue Op, SelectionDAG &DAG) const {
   case ISD::BUILD_VECTOR:
     return LowerBUILD_VECTOR(Op, DAG);
   case ISD::BITCAST:
-    return LowerBITCAST(Op, DAG);
+    return SDValue();
   case ISD::EXTRACT_SUBVECTOR:
     return Op;
   case ISD::EXTRACT_VECTOR_ELT:
diff --git a/llvm/lib/Target/NVPTX/NVPTXISelLowering.h b/llvm/lib/Target/NVPTX/NVPTXISelLowering.h
index 4a98fe21b81dc6..446ff1536d36cf 100644
--- a/llvm/lib/Target/NVPTX/NVPTXISelLowering.h
+++ b/llvm/lib/Target/NVPTX/NVPTXISelLowering.h
@@ -265,8 +265,6 @@ class NVPTXTargetLowering : public TargetLowering {
   const NVPTXSubtarget &STI; // cache the subtarget here
   SDValue getParamSymbol(SelectionDAG &DAG, int idx, EVT) const;
 
-  SDValue LowerBITCAST(SDValue Op, SelectionDAG &DAG) const;
-
   SDValue LowerBUILD_VECTOR(SDValue Op, SelectionDAG &DAG) const;
   SDValue LowerCONCAT_VECTORS(SDValue Op, SelectionDAG &DAG) const;
   SDValue LowerEXTRACT_VECTOR_ELT(SDValue Op, SelectionDAG &DAG) const;

``````````

</details>


https://github.com/llvm/llvm-project/pull/120903