[flang][cuda] Avoid generating data transfer when calling size intrinsic

[clementval]

cuf.data_transfer was wrongly generated when calling the size intrinsic on a device allocatable variable. Since the descriptor is available on the host, there is no transfer needed.

Add DescriptorInquiry in the CollectCudaSymbolsHelper to filter out symbols that are not needed for the transfer decision to be made.

[llvmbot]

@llvm/pr-subscribers-flang-semantics

@llvm/pr-subscribers-flang-fir-hlfir

Author: Valentin Clement (バレンタイン クレメン) (clementval)

Changes

cuf.data_transfer was wrongly generated when calling the size intrinsic on a device allocatable variable. Since the descriptor is available on the host, there is no transfer needed.

Add DescriptorInquiry in the CollectCudaSymbolsHelper to filter out symbols that are not needed for the transfer decision to be made.

---

Full diff: https://github.com/llvm/llvm-project/pull/108081.diff

2 Files Affected:

• (modified) flang/lib/Evaluate/tools.cpp (+3)
• (modified) flang/test/Lower/CUDA/cuda-data-transfer.cuf (+10)

diff --git a/flang/lib/Evaluate/tools.cpp b/flang/lib/Evaluate/tools.cpp
index 6b3db619c1e2f1..400f27aef98da6 100644
--- a/flang/lib/Evaluate/tools.cpp
+++ b/flang/lib/Evaluate/tools.cpp
@@ -1011,6 +1011,9 @@ struct CollectCudaSymbolsHelper : public SetTraverse<CollectCudaSymbolsHelper,
   }
   // Overload some of the operator() to filter out the symbols that are not
   // of interest for CUDA data transfer logic.
+  semantics::UnorderedSymbolSet operator()(const DescriptorInquiry &) const {
+    return {};
+  }
   semantics::UnorderedSymbolSet operator()(const Subscript &) const {
     return {};
   }
diff --git a/flang/test/Lower/CUDA/cuda-data-transfer.cuf b/flang/test/Lower/CUDA/cuda-data-transfer.cuf
index bcbac9c3031423..11f1f33d7cb587 100644
--- a/flang/test/Lower/CUDA/cuda-data-transfer.cuf
+++ b/flang/test/Lower/CUDA/cuda-data-transfer.cuf
@@ -353,3 +353,13 @@ end subroutine
 ! CHECK-LABEL: func.func @_QPsub17()
 ! CHECK: cuf.kernel<<<*, *>>>
 ! CHECK-NOT: cuf.data_transfer
+
+subroutine sub18()
+  integer, device, allocatable :: a(:)
+  integer :: isz
+
+  isz = size(a)
+end subroutine
+
+! CHECK-LABEL: func.func @_QPsub18()
+! CHECK-NOT: cuf.data_transfer

[vzakhari]

LGTM