[PowerPC] Zero-extend the compare operand for ATOMIC_CMP_SWAP

Part of the fix for https://bugs.llvm.org/show_bug.cgi?id=35812.
This patch ensures that the compare operand for the atomic compare and swap
is properly zero-extended to 32 bits if applicable.
A follow-up commit will fix the extension for the SETCC node generated when
expanding an ATOMIC_CMP_SWAP_WITH_SUCCESS. That will complete the bug fix.

Differential Revision: https://reviews.llvm.org/D41856

llvm-svn: 322372

3 files changed, 61 insertions, 0 deletions

diff --git a/llvm/lib/Target/PowerPC/PPCISelLowering.cpp b/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
index d31d499ff32..3c09ab8d755 100644
--- a/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
+++ b/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
@@ -142,6 +142,9 @@ PPCTargetLowering::PPCTargetLowering(const PPCTargetMachine &TM,
   setOperationAction(ISD::BITREVERSE, MVT::i32, Legal);
   setOperationAction(ISD::BITREVERSE, MVT::i64, Legal);
 
+  // Sub-word ATOMIC_CMP_SWAP need to ensure that the input is zero-extended.
+  setOperationAction(ISD::ATOMIC_CMP_SWAP, MVT::i32, Custom);
+
   // PowerPC has an i16 but no i8 (or i1) SEXTLOAD.
   for (MVT VT : MVT::integer_valuetypes()) {
     setLoadExtAction(ISD::SEXTLOAD, VT, MVT::i1, Promote);
@@ -1154,6 +1157,8 @@ const char *PPCTargetLowering::getTargetNodeName(unsigned Opcode) const {
   case PPCISD::Hi:              return "PPCISD::Hi";
   case PPCISD::Lo:              return "PPCISD::Lo";
   case PPCISD::TOC_ENTRY:       return "PPCISD::TOC_ENTRY";
+  case PPCISD::ATOMIC_CMP_SWAP_8: return "PPCISD::ATOMIC_CMP_SWAP_8";
+  case PPCISD::ATOMIC_CMP_SWAP_16: return "PPCISD::ATOMIC_CMP_SWAP_16";
   case PPCISD::DYNALLOC:        return "PPCISD::DYNALLOC";
   case PPCISD::DYNAREAOFFSET:   return "PPCISD::DYNAREAOFFSET";
   case PPCISD::GlobalBaseReg:   return "PPCISD::GlobalBaseReg";
@@ -8834,6 +8839,42 @@ SDValue PPCTargetLowering::LowerBSWAP(SDValue Op, SelectionDAG &DAG) const {
   return Op;
 }
 
+// ATOMIC_CMP_SWAP for i8/i16 needs to zero-extend its input since it will be
+// compared to a value that is atomically loaded (atomic loads zero-extend).
+SDValue PPCTargetLowering::LowerATOMIC_CMP_SWAP(SDValue Op,
+                                                SelectionDAG &DAG) const {
+  assert(Op.getOpcode() == ISD::ATOMIC_CMP_SWAP &&
+         "Expecting an atomic compare-and-swap here.");
+  SDLoc dl(Op);
+  auto *AtomicNode = cast<AtomicSDNode>(Op.getNode());
+  EVT MemVT = AtomicNode->getMemoryVT();
+  if (MemVT.getSizeInBits() >= 32)
+    return Op;
+
+  SDValue CmpOp = Op.getOperand(2);
+  // If this is already correctly zero-extended, leave it alone.
+  auto HighBits = APInt::getHighBitsSet(32, 32 - MemVT.getSizeInBits());
+  if (DAG.MaskedValueIsZero(CmpOp, HighBits))
+    return Op;
+
+  // Clear the high bits of the compare operand.
+  unsigned MaskVal = (1 << MemVT.getSizeInBits()) - 1;
+  SDValue NewCmpOp =
+    DAG.getNode(ISD::AND, dl, MVT::i32, CmpOp,
+                DAG.getConstant(MaskVal, dl, MVT::i32));
+
+  // Replace the existing compare operand with the properly zero-extended one.
+  SmallVector<SDValue, 4> Ops;
+  for (int i = 0, e = AtomicNode->getNumOperands(); i < e; i++)
+    Ops.push_back(AtomicNode->getOperand(i));
+  Ops[2] = NewCmpOp;
+  MachineMemOperand *MMO = AtomicNode->getMemOperand();
+  SDVTList Tys = DAG.getVTList(MVT::i32, MVT::Other);
+  auto NodeTy =
+    (MemVT == MVT::i8) ? PPCISD::ATOMIC_CMP_SWAP_8 : PPCISD::ATOMIC_CMP_SWAP_16;
+  return DAG.getMemIntrinsicNode(NodeTy, dl, Tys, Ops, MemVT, MMO);
+}
+
 SDValue PPCTargetLowering::LowerSIGN_EXTEND_INREG(SDValue Op,
                                                   SelectionDAG &DAG) const {
   SDLoc dl(Op);
@@ -9325,6 +9366,8 @@ SDValue PPCTargetLowering::LowerOperation(SDValue Op, SelectionDAG &DAG) const {
     return LowerREM(Op, DAG);
   case ISD::BSWAP:
     return LowerBSWAP(Op, DAG);
+  case ISD::ATOMIC_CMP_SWAP:
+    return LowerATOMIC_CMP_SWAP(Op, DAG);
   }
 }
 
diff --git a/llvm/lib/Target/PowerPC/PPCISelLowering.h b/llvm/lib/Target/PowerPC/PPCISelLowering.h
index b119e5b4a56..b3215a84829 100644
--- a/llvm/lib/Target/PowerPC/PPCISelLowering.h
+++ b/llvm/lib/Target/PowerPC/PPCISelLowering.h
@@ -430,6 +430,11 @@ namespace llvm {
       /// The 4xf32 load used for v4i1 constants.
       QVLFSb,
 
+      /// ATOMIC_CMP_SWAP - the exact same as the target-independent nodes
+      /// except they ensure that the compare input is zero-extended for
+      /// sub-word versions because the atomic loads zero-extend.
+      ATOMIC_CMP_SWAP_8, ATOMIC_CMP_SWAP_16,
+
       /// GPRC = TOC_ENTRY GA, TOC
       /// Loads the entry for GA from the TOC, where the TOC base is given by
       /// the last operand.
@@ -955,6 +960,7 @@ namespace llvm {
     SDValue LowerINTRINSIC_VOID(SDValue Op, SelectionDAG &DAG) const;
     SDValue LowerREM(SDValue Op, SelectionDAG &DAG) const;
     SDValue LowerBSWAP(SDValue Op, SelectionDAG &DAG) const;
+    SDValue LowerATOMIC_CMP_SWAP(SDValue Op, SelectionDAG &DAG) const;
     SDValue LowerSCALAR_TO_VECTOR(SDValue Op, SelectionDAG &DAG) const;
     SDValue LowerSIGN_EXTEND_INREG(SDValue Op, SelectionDAG &DAG) const;
     SDValue LowerMUL(SDValue Op, SelectionDAG &DAG) const;
diff --git a/llvm/lib/Target/PowerPC/PPCInstrInfo.td b/llvm/lib/Target/PowerPC/PPCInstrInfo.td
index a932d05b24e..43dcc4479cf 100644
--- a/llvm/lib/Target/PowerPC/PPCInstrInfo.td
+++ b/llvm/lib/Target/PowerPC/PPCInstrInfo.td
@@ -257,6 +257,13 @@ def PPCvcmp_o     : SDNode<"PPCISD::VCMPo", SDT_PPCvcmp, [SDNPOutGlue]>;
 def PPCcondbranch : SDNode<"PPCISD::COND_BRANCH", SDT_PPCcondbr,
                            [SDNPHasChain, SDNPOptInGlue]>;
 
+// PPC-specific atomic operations.
+def PPCatomicCmpSwap_8 :
+  SDNode<"PPCISD::ATOMIC_CMP_SWAP_8", SDTAtomic3,
+         [SDNPHasChain, SDNPMayStore, SDNPMayLoad, SDNPMemOperand]>;
+def PPCatomicCmpSwap_16 :
+  SDNode<"PPCISD::ATOMIC_CMP_SWAP_16", SDTAtomic3,
+         [SDNPHasChain, SDNPMayStore, SDNPMayLoad, SDNPMemOperand]>;
 def PPClbrx       : SDNode<"PPCISD::LBRX", SDT_PPClbrx,
                            [SDNPHasChain, SDNPMayLoad, SDNPMemOperand]>;
 def PPCstbrx      : SDNode<"PPCISD::STBRX", SDT_PPCstbrx,
@@ -1710,6 +1717,11 @@ let usesCustomInserter = 1 in {
   }
 }
 
+def : Pat<(PPCatomicCmpSwap_8 xoaddr:$ptr, i32:$old, i32:$new),
+        (ATOMIC_CMP_SWAP_I8 xoaddr:$ptr, i32:$old, i32:$new)>;
+def : Pat<(PPCatomicCmpSwap_16 xoaddr:$ptr, i32:$old, i32:$new),
+        (ATOMIC_CMP_SWAP_I16 xoaddr:$ptr, i32:$old, i32:$new)>;
+
 // Instructions to support atomic operations
 let mayLoad = 1, mayStore = 0, hasSideEffects = 0 in {
 def LBARX : XForm_1<31,  52, (outs gprc:$rD), (ins memrr:$src),