[flang-commits] [flang] 0aa982f - [flang][cuda] Add restriction on implicit data transfer (#87720)

[via flang-commits]

Author: Valentin Clement (バレンタイン クレメン)
Date: 2024-04-05T13:40:38-07:00
New Revision: 0aa982fb326effa62277028375b5c346e0f6fcf5

URL: https://github.com/llvm/llvm-project/commit/0aa982fb326effa62277028375b5c346e0f6fcf5
DIFF: https://github.com/llvm/llvm-project/commit/0aa982fb326effa62277028375b5c346e0f6fcf5.diff

LOG: [flang][cuda] Add restriction on implicit data transfer (#87720)

In section 3.4.2, some example of illegal data transfer using expression
are given. One of it is when multiple device objects are part of an
expression in the rhs. Current implementation allow a single device
object in such case. This patch adds a similar restriction.

Added: 
    flang/test/Semantics/cuf11.cuf

Modified: 
    flang/include/flang/Evaluate/tools.h
    flang/lib/Semantics/check-cuda.cpp
    flang/lib/Semantics/check-cuda.h

Removed: 
    


################################################################################
diff  --git a/flang/include/flang/Evaluate/tools.h b/flang/include/flang/Evaluate/tools.h
index 29065c9f01ecf2..ca14c144af2d60 100644
--- a/flang/include/flang/Evaluate/tools.h
+++ b/flang/include/flang/Evaluate/tools.h
@@ -1227,18 +1227,24 @@ bool CheckForCoindexedObject(parser::ContextualMessages &,
     const std::optional<ActualArgument> &, const std::string &procName,
     const std::string &argName);
 
-/// Check if any of the symbols part of the expression has a cuda data
-/// attribute.
-inline bool HasCUDAAttrs(const Expr<SomeType> &expr) {
+// Get the number of distinct symbols with CUDA attribute in the expression.
+template <typename A> inline int GetNbOfCUDASymbols(const A &expr) {
+  semantics::UnorderedSymbolSet symbols;
   for (const Symbol &sym : CollectSymbols(expr)) {
     if (const auto *details =
             sym.GetUltimate().detailsIf<semantics::ObjectEntityDetails>()) {
       if (details->cudaDataAttr()) {
-        return true;
+        symbols.insert(sym);
       }
     }
   }
-  return false;
+  return symbols.size();
+}
+
+// Check if any of the symbols part of the expression has a CUDA data
+// attribute.
+template <typename A> inline bool HasCUDAAttrs(const A &expr) {
+  return GetNbOfCUDASymbols(expr) > 0;
 }
 
 /// Check if the expression is a mix of host and device variables that require

diff  --git a/flang/lib/Semantics/check-cuda.cpp b/flang/lib/Semantics/check-cuda.cpp
index c0c6ff4c1a2ba3..39bfc47a8eb1ee 100644
--- a/flang/lib/Semantics/check-cuda.cpp
+++ b/flang/lib/Semantics/check-cuda.cpp
@@ -9,12 +9,14 @@
 #include "check-cuda.h"
 #include "flang/Common/template.h"
 #include "flang/Evaluate/fold.h"
+#include "flang/Evaluate/tools.h"
 #include "flang/Evaluate/traverse.h"
 #include "flang/Parser/parse-tree-visitor.h"
 #include "flang/Parser/parse-tree.h"
 #include "flang/Parser/tools.h"
 #include "flang/Semantics/expression.h"
 #include "flang/Semantics/symbol.h"
+#include "flang/Semantics/tools.h"
 
 // Once labeled DO constructs have been canonicalized and their parse subtrees
 // transformed into parser::DoConstructs, scan the parser::Blocks of the program
@@ -413,4 +415,18 @@ void CUDAChecker::Enter(const parser::CUFKernelDoConstruct &x) {
   }
 }
 
+void CUDAChecker::Enter(const parser::AssignmentStmt &x) {
+  const evaluate::Assignment *assign{semantics::GetAssignment(x)};
+  int nbLhs{evaluate::GetNbOfCUDASymbols(assign->lhs)};
+  int nbRhs{evaluate::GetNbOfCUDASymbols(assign->rhs)};
+  auto lhsLoc{std::get<parser::Variable>(x.t).GetSource()};
+
+  // device to host transfer with more than one device object on the rhs is not
+  // legal.
+  if (nbLhs == 0 && nbRhs > 1) {
+    context_.Say(lhsLoc,
+        "More than one reference to a CUDA object on the right hand side of the assigment"_err_en_US);
+  }
+}
+
 } // namespace Fortran::semantics

diff  --git a/flang/lib/Semantics/check-cuda.h b/flang/lib/Semantics/check-cuda.h
index d863795f16a7c2..aa0cb46360bef5 100644
--- a/flang/lib/Semantics/check-cuda.h
+++ b/flang/lib/Semantics/check-cuda.h
@@ -17,6 +17,7 @@ struct Program;
 class Messages;
 struct Name;
 class CharBlock;
+struct AssignmentStmt;
 struct ExecutionPartConstruct;
 struct ExecutableConstruct;
 struct ActionStmt;
@@ -38,6 +39,7 @@ class CUDAChecker : public virtual BaseChecker {
   void Enter(const parser::FunctionSubprogram &);
   void Enter(const parser::SeparateModuleSubprogram &);
   void Enter(const parser::CUFKernelDoConstruct &);
+  void Enter(const parser::AssignmentStmt &);
 
 private:
   SemanticsContext &context_;

diff  --git a/flang/test/Semantics/cuf11.cuf b/flang/test/Semantics/cuf11.cuf
new file mode 100644
index 00000000000000..96108e2b245560
--- /dev/null
+++ b/flang/test/Semantics/cuf11.cuf
@@ -0,0 +1,12 @@
+! RUN: %python %S/test_errors.py %s %flang_fc1
+
+subroutine sub1()
+  real, device :: adev(10), bdev(10)
+  real :: ahost(10)
+
+!ERROR: More than one reference to a CUDA object on the right hand side of the assigment
+  ahost = adev + bdev
+
+  ahost = adev + adev
+
+end subroutine