[SelectionDAG] Legalize vector types for atomic load

Scalarize vector of atomic load in SelectionDAG.

Author: jofrn

llvm/lib/CodeGen/SelectionDAG/LegalizeTypes.h

@@ -860,6 +860,7 @@ class LLVM_LIBRARY_VISIBILITY DAGTypeLegalizer {
   SDValue ScalarizeVecRes_ExpOp(SDNode *N);
   SDValue ScalarizeVecRes_INSERT_VECTOR_ELT(SDNode *N);
   SDValue ScalarizeVecRes_LOAD(LoadSDNode *N);
+  SDValue ScalarizeVecRes_ATOMIC_LOAD(AtomicSDNode *N);
   SDValue ScalarizeVecRes_SCALAR_TO_VECTOR(SDNode *N);
   SDValue ScalarizeVecRes_VSELECT(SDNode *N);
   SDValue ScalarizeVecRes_SELECT(SDNode *N);

llvm/lib/CodeGen/SelectionDAG/LegalizeVectorTypes.cpp

@@ -60,6 +60,9 @@ void DAGTypeLegalizer::ScalarizeVectorResult(SDNode *N, unsigned ResNo) {
   case ISD::FP_ROUND:          R = ScalarizeVecRes_FP_ROUND(N); break;
   case ISD::FPOWI:             R = ScalarizeVecRes_ExpOp(N); break;
   case ISD::INSERT_VECTOR_ELT: R = ScalarizeVecRes_INSERT_VECTOR_ELT(N); break;
+  case ISD::ATOMIC_LOAD:
+    R = ScalarizeVecRes_ATOMIC_LOAD(cast<AtomicSDNode>(N));
+    break;
   case ISD::LOAD:           R = ScalarizeVecRes_LOAD(cast<LoadSDNode>(N));break;
   case ISD::SCALAR_TO_VECTOR:  R = ScalarizeVecRes_SCALAR_TO_VECTOR(N); break;
   case ISD::SIGN_EXTEND_INREG: R = ScalarizeVecRes_InregOp(N); break;
@@ -451,6 +454,19 @@ SDValue DAGTypeLegalizer::ScalarizeVecRes_INSERT_VECTOR_ELT(SDNode *N) {
   return Op;
 }
 
+SDValue DAGTypeLegalizer::ScalarizeVecRes_ATOMIC_LOAD(AtomicSDNode *N) {
+
+  SDValue Result = DAG.getAtomic(ISD::ATOMIC_LOAD, SDLoc(N),
+      N->getMemoryVT().getVectorElementType(),
+      N->getValueType(0).getVectorElementType(),
+      N->getChain(), N->getBasePtr(), N->getMemOperand());
+
+  // Legalize the chain result - switch anything that used the old chain to
+  // use the new one.
+  ReplaceValueWith(SDValue(N, 1), Result.getValue(1));
+  return Result;
+}
+
 SDValue DAGTypeLegalizer::ScalarizeVecRes_LOAD(LoadSDNode *N) {
   assert(N->isUnindexed() && "Indexed vector load?");
 

llvm/test/CodeGen/Generic/atomic-scalarization.ll

@@ -0,0 +1,17 @@
+; RUN: llc %s --print-after-isel --disable-verify 2>&1 | FileCheck %s
+
+define i32 @atomic_scalar() {
+; CHECK: # After Instruction Selection:
+; CHECK-NEXT: # Machine code for function atomic_scalar: IsSSA, TracksLiveness
+; CHECK-NEXT: Frame Objects:
+; CHECK-NEXT:   fi#0: size=4, align=4, at location [SP+8]
+; CHECK:      bb.0 (%ir-block.0):
+; CHECK-NEXT:   %0:gr32 = MOV32rm %stack.0, 1, $noreg, 0, $noreg :: (dereferenceable load acquire (s32) from %ir.1)
+; CHECK-NEXT:   $eax = COPY %0:gr32
+; CHECK-NEXT:   RET 0, $eax
+; CHECK:      # End machine code for function atomic_scalar.
+  %1 = alloca <1 x i32>
+  %2 = load atomic <1 x i32>, ptr %1 acquire, align 4
+  %3 = extractelement <1 x i32> %2, i32 0
+  ret i32 %3
+}