[llvm] [DAGCombiner] Add some very basic folds for ADDRSPACECAST (PR #127733)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-nvptx

Author: Alex MacLean (AlexMaclean)

<details>
<summary>Changes</summary>

Fold an ADDRSPACECAST of another ADDRPSACECAST into a single cast or remove them completely and forward the inner ASC operand.

---
Full diff: https://github.com/llvm/llvm-project/pull/127733.diff


2 Files Affected:

- (modified) llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp (+21) 
- (added) llvm/test/CodeGen/NVPTX/addrspacecast-folding.ll (+32) 


``````````diff
diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index c6fd72b6b76f4..b0af55722f7ff 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/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);
diff --git a/llvm/test/CodeGen/NVPTX/addrspacecast-folding.ll b/llvm/test/CodeGen/NVPTX/addrspacecast-folding.ll
new file mode 100644
index 0000000000000..11c2b6782e0d3
--- /dev/null
+++ b/llvm/test/CodeGen/NVPTX/addrspacecast-folding.ll
@@ -0,0 +1,32 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 5
+; RUN: llc < %s -mcpu=sm_20 -O0 | FileCheck %s
+; RUN: %if ptxas %{ llc < %s -mcpu=sm_20 -O0 | %ptxas-verify %}
+
+target triple = "nvptx64-unknown-unknown"
+
+define ptr @test1(ptr %p) {
+; CHECK-LABEL: test1(
+; CHECK:       {
+; CHECK-NEXT:    .reg .b64 %rd<2>;
+; CHECK-EMPTY:
+; CHECK-NEXT:  // %bb.0:
+; CHECK-NEXT:    ld.param.u64 %rd1, [test1_param_0];
+; 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
+  ret ptr %b
+}
+
+define ptr addrspace(1) @test2(ptr addrspace(5) %p) {
+; CHECK-LABEL: test2(
+; CHECK:       {
+; CHECK-NEXT:    .reg .b64 %rd<2>;
+; CHECK-EMPTY:
+; CHECK-NEXT:  // %bb.0:
+; CHECK-NEXT:    ld.param.u64 %rd1, [test2_param_0];
+; CHECK-NEXT:    ret;
+  %a = addrspacecast ptr addrspace(5) %p to ptr
+  %b = addrspacecast ptr %a to ptr addrspace(1)
+  ret ptr addrspace(1) %b
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/127733