R600: Add comments to subword private address load lowering code

v2: Use C++ comments and end with periods

Signed-off-by: Jan Vesely <jan.vesely@rutgers.edu>
Reviewed-by: Matt Arsenault <Matthew.Arsenault@amd.com>
llvm-svn: 238228

1 files changed, 13 insertions, 0 deletions

diff --git a/llvm/lib/Target/R600/AMDGPUISelLowering.cpp b/llvm/lib/Target/R600/AMDGPUISelLowering.cpp
index 880240c51a8..d00ae78c99b 100644
--- a/llvm/lib/Target/R600/AMDGPUISelLowering.cpp
+++ b/llvm/lib/Target/R600/AMDGPUISelLowering.cpp
@@ -1451,22 +1451,34 @@ SDValue AMDGPUTargetLowering::LowerLOAD(SDValue Op, SelectionDAG &DAG) const {
       ExtType == ISD::NON_EXTLOAD || Load->getMemoryVT().bitsGE(MVT::i32))
     return SDValue();
 
+  // <SI && AS=PRIVATE && EXTLOAD && size < 32bit,
+  // register (2-)byte extract.
 
+  // Get Register holding the target.
   SDValue Ptr = DAG.getNode(ISD::SRL, DL, MVT::i32, Load->getBasePtr(),
                             DAG.getConstant(2, DL, MVT::i32));
+  // Load the Register.
   SDValue Ret = DAG.getNode(AMDGPUISD::REGISTER_LOAD, DL, Op.getValueType(),
                             Load->getChain(), Ptr,
                             DAG.getTargetConstant(0, DL, MVT::i32),
                             Op.getOperand(2));
+
+  // Get offset within the register.
   SDValue ByteIdx = DAG.getNode(ISD::AND, DL, MVT::i32,
                                 Load->getBasePtr(),
                                 DAG.getConstant(0x3, DL, MVT::i32));
+
+  // Bit offset of target byte (byteIdx * 8).
   SDValue ShiftAmt = DAG.getNode(ISD::SHL, DL, MVT::i32, ByteIdx,
                                  DAG.getConstant(3, DL, MVT::i32));
 
+  // Shift to the right.
   Ret = DAG.getNode(ISD::SRL, DL, MVT::i32, Ret, ShiftAmt);
 
+  // Eliminate the upper bits by setting them to ...
   EVT MemEltVT = MemVT.getScalarType();
+
+  // ... ones.
   if (ExtType == ISD::SEXTLOAD) {
     SDValue MemEltVTNode = DAG.getValueType(MemEltVT);
 
@@ -1478,6 +1490,7 @@ SDValue AMDGPUTargetLowering::LowerLOAD(SDValue Op, SelectionDAG &DAG) const {
     return DAG.getMergeValues(Ops, DL);
   }
 
+  // ... or zeros.
   SDValue Ops[] = {
     DAG.getZeroExtendInReg(Ret, DL, MemEltVT),
     Load->getChain()