[DAGCombiner] Add very basic folds for ADDRSPACECAST

Author: AlexMaclean

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

@@ -488,6 +488,7 @@ namespace {
     SDValue visitTRUNCATE(SDNode *N);
     SDValue visitTRUNCATE_USAT_U(SDNode *N);
     SDValue visitBITCAST(SDNode *N);
+    SDValue visitADDRSPACECAST(SDNode *N);
     SDValue visitFREEZE(SDNode *N);
     SDValue visitBUILD_PAIR(SDNode *N);
     SDValue visitFADD(SDNode *N);
@@ -1920,6 +1921,7 @@ SDValue DAGCombiner::visit(SDNode *N) {
   case ISD::TRUNCATE:           return visitTRUNCATE(N);
   case ISD::TRUNCATE_USAT_U:    return visitTRUNCATE_USAT_U(N);
   case ISD::BITCAST:            return visitBITCAST(N);
+  case ISD::ADDRSPACECAST:      return visitADDRSPACECAST(N);
   case ISD::BUILD_PAIR:         return visitBUILD_PAIR(N);
   case ISD::FADD:               return visitFADD(N);
   case ISD::STRICT_FADD:        return visitSTRICT_FADD(N);
@@ -16054,6 +16056,25 @@ SDValue DAGCombiner::visitBITCAST(SDNode *N) {
   return SDValue();
 }
 
+SDValue DAGCombiner::visitADDRSPACECAST(SDNode *N) {
+  auto *ASCN1 = cast<AddrSpaceCastSDNode>(N);
+
+  if (auto *ASCN2 = dyn_cast<AddrSpaceCastSDNode>(ASCN1->getOperand(0))) {
+    assert(ASCN2->getDestAddressSpace() == ASCN1->getSrcAddressSpace());
+
+    // Fold asc[B -> A](asc[A -> B](x)) -> x
+    if (ASCN1->getDestAddressSpace() == ASCN2->getSrcAddressSpace())
+      return ASCN2->getOperand(0);
+
+    // Fold asc[B -> C](asc[A -> B](x)) -> asc[A -> C](x)
+    return DAG.getAddrSpaceCast(
+        SDLoc(N), N->getValueType(0), ASCN2->getOperand(0),
+        ASCN2->getSrcAddressSpace(), ASCN1->getDestAddressSpace());
+  }
+
+  return SDValue();
+}
+
 SDValue DAGCombiner::visitBUILD_PAIR(SDNode *N) {
   EVT VT = N->getValueType(0);
   return CombineConsecutiveLoads(N, VT);

llvm/test/CodeGen/NVPTX/addrspacecast-folding.ll

@@ -7,13 +7,11 @@ target triple = "nvptx64-unknown-unknown"
 define ptr @test1(ptr %p) {
 ; CHECK-LABEL: test1(
 ; CHECK:       {
-; CHECK-NEXT:    .reg .b64 %rd<4>;
+; CHECK-NEXT:    .reg .b64 %rd<2>;
 ; CHECK-EMPTY:
 ; CHECK-NEXT:  // %bb.0:
 ; CHECK-NEXT:    ld.param.u64 %rd1, [test1_param_0];
-; CHECK-NEXT:    cvta.to.local.u64 %rd2, %rd1;
-; CHECK-NEXT:    cvta.local.u64 %rd3, %rd2;
-; CHECK-NEXT:    st.param.b64 [func_retval0], %rd3;
+; CHECK-NEXT:    st.param.b64 [func_retval0], %rd1;
 ; CHECK-NEXT:    ret;
   %a = addrspacecast ptr %p to ptr addrspace(5)
   %b = addrspacecast ptr addrspace(5) %a to ptr
@@ -23,13 +21,10 @@ define ptr @test1(ptr %p) {
 define ptr addrspace(1) @test2(ptr addrspace(5) %p) {
 ; CHECK-LABEL: test2(
 ; CHECK:       {
-; CHECK-NEXT:    .reg .b64 %rd<4>;
+; CHECK-NEXT:    .reg .b64 %rd<2>;
 ; CHECK-EMPTY:
 ; CHECK-NEXT:  // %bb.0:
 ; CHECK-NEXT:    ld.param.u64 %rd1, [test2_param_0];
-; CHECK-NEXT:    cvta.local.u64 %rd2, %rd1;
-; CHECK-NEXT:    cvta.to.global.u64 %rd3, %rd2;
-; CHECK-NEXT:    st.param.b64 [func_retval0], %rd3;
 ; CHECK-NEXT:    ret;
   %a = addrspacecast ptr addrspace(5) %p to ptr
   %b = addrspacecast ptr %a to ptr addrspace(1)