[llvm] [Offload]: Skip copying of unused kernel-mapped data (PR #124723)

[Johannes Doerfert via llvm-commits]

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@@ -1197,6 +1197,82 @@ class PrivateArgumentManagerTy {
   }
 };
 
+/// Try to find redundant mappings associated with a kernel launch,
+/// and provide a masked version of the kernel argument types that
+/// avoid redundant to data transfers between the host and device.
+static std::unique_ptr<int64_t[]>
+maskRedundantTransfers(DeviceTy &Device, int32_t ArgNum, int64_t *ArgTypes,
+                       int64_t *ArgSizes, map_var_info_t *ArgNames,
+                       void **ArgPtrs, void **ArgMappers) {
+  std::unique_ptr<int64_t[]> ArgTypesOverride =
+      std::make_unique<int64_t[]>(ArgNum);
+
+  MappingInfoTy &MappingInfo = Device.getMappingInfo();
+  MappingInfoTy::HDTTMapAccessorTy HDTTMap =
+      MappingInfo.HostDataToTargetMap.getExclusiveAccessor();
+
+  int64_t UnusedArgs = 0;
+
+  for (int32_t I = 0; I < ArgNum; ++I) {
+    tgt_map_type ArgType = (tgt_map_type)ArgTypes[I];
+
+    // Check for unused implicit mappings
+    bool IsArgUnused = ArgType == OMP_TGT_MAPTYPE_NONE;
+
+    // Check for unused `map(buf[0:size])` mappings
+    IsArgUnused |= ArgType == OMP_TGT_MAPTYPE_FROM ||
+                   ArgType == OMP_TGT_MAPTYPE_TO ||
+                   ArgType == (OMP_TGT_MAPTYPE_FROM | OMP_TGT_MAPTYPE_TO);
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jdoerfert wrote:

Are there no other flags allowed? It might be so, just checking.

https://github.com/llvm/llvm-project/pull/124723