[flang-commits] [flang] [flang][cuda] Fix CUDA generic matching with omitted optional args (PR #197275)

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<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-flang-semantics

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

<details>
<summary>Changes</summary>

Skip omitted optional arguments when computing CUDA address-space matching distances, so -gpu=unified overload resolution does not compare expanded dummy-argument lists of different sizes. Adds a regression covering a unified-memory overload with optional extras.

---
Full diff: https://github.com/llvm/llvm-project/pull/197275.diff


2 Files Affected:

- (modified) flang/lib/Semantics/expression.cpp (+4) 
- (modified) flang/test/Semantics/cuf14.cuf (+19) 


``````````diff
diff --git a/flang/lib/Semantics/expression.cpp b/flang/lib/Semantics/expression.cpp
index 066ead7fc28e8..dad401f0baa74 100644
--- a/flang/lib/Semantics/expression.cpp
+++ b/flang/lib/Semantics/expression.cpp
@@ -2965,6 +2965,10 @@ static CudaMatchingDistance ComputeCudaMatchingDistance(
   for (std::size_t i{0}; i < dummies.size(); ++i) {
     const characteristics::DummyArgument &dummy{dummies[i]};
     const std::optional<ActualArgument> &actual{actuals[i]};
+    if (!actual) {
+      // Omitted optional arguments do not affect CUDA matching distances.
+      continue;
+    }
     int d{GetMatchingDistance(features, dummy, actual)};
     if (d == cudaInfMatchingValue) {
       distance.isInfinite = true;
diff --git a/flang/test/Semantics/cuf14.cuf b/flang/test/Semantics/cuf14.cuf
index 29c9ecf90677f..28bd410ad0034 100644
--- a/flang/test/Semantics/cuf14.cuf
+++ b/flang/test/Semantics/cuf14.cuf
@@ -19,6 +19,11 @@ module matching
     module procedure sub_managed
   end interface
 
+  interface optional_extra_args
+    module procedure sub_host_3args
+    module procedure sub_unified_5args
+  end interface
+
 contains
   subroutine sub_host(a)
     integer :: a(:)
@@ -35,21 +40,35 @@ contains
   subroutine sub_unified(a)
     integer, unified :: a(:)
   end
+
+  subroutine sub_host_3args(a, b, c)
+    integer :: a(:)
+    integer :: b, c
+  end
+
+  subroutine sub_unified_5args(a, b, c, d, e)
+    integer, unified :: a(:)
+    integer :: b, c
+    integer, optional :: d, e
+  end
 end module
 
 program m
   use matching
 
   integer, allocatable :: actual_host(:)
+  integer :: i
 
   allocate(actual_host(10))
 
   call host_and_device(actual_host)     ! Should resolve to sub_device
   call all(actual_host)                 ! Should resolved to unified
   call all_without_unified(actual_host) ! Should resolved to managed
+  call optional_extra_args(actual_host, i, i) ! Should resolve to sub_unified_5args
 end
 
 ! CHECK: fir.call @_QMmatchingPsub_device
 ! CHECK: fir.call @_QMmatchingPsub_unified
 ! CHECK: fir.call @_QMmatchingPsub_managed
+! CHECK: fir.call @_QMmatchingPsub_unified_5args
 

``````````

</details>


https://github.com/llvm/llvm-project/pull/197275