[Openmp-commits] [openmp] 0c7a487 - [libomptarget] Keep the Shadow Pointer Map up-to-date

[George Rokos via Openmp-commits]

Author: George Rokos
Date: 2021-07-14T15:19:58-07:00
New Revision: 0c7a4870c5b63935b7f0c7cbc380b497341dd203

URL: https://github.com/llvm/llvm-project/commit/0c7a4870c5b63935b7f0c7cbc380b497341dd203
DIFF: https://github.com/llvm/llvm-project/commit/0c7a4870c5b63935b7f0c7cbc380b497341dd203.diff

LOG: [libomptarget] Keep the Shadow Pointer Map up-to-date

D105812 introduced a regression where if a PTR_AND_OBJ entry was mapped on the device, then the OBJ was deallocated and then reallocated at a different address, the Shadow Pointer Map would still contain an entry for the PTR but pointing to the old address. This caused test `env/base_ptr_ref_count.c` to fail.

Differential Revision: https://reviews.llvm.org/D105947

Added: 
    

Modified: 
    openmp/libomptarget/src/omptarget.cpp

Removed: 
    


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diff  --git a/openmp/libomptarget/src/omptarget.cpp b/openmp/libomptarget/src/omptarget.cpp
index 0255f94599ee1..3b1c5a8742f4c 100644
--- a/openmp/libomptarget/src/omptarget.cpp
+++ b/openmp/libomptarget/src/omptarget.cpp
@@ -564,9 +564,20 @@ int targetDataBegin(ident_t *loc, DeviceTy &Device, int32_t arg_num,
 
       Device.ShadowMtx.lock();
       auto Entry = Device.ShadowPtrMap.find(Pointer_HstPtrBegin);
-      // If this pointer is not in the map we need to insert it.
-      if (Entry == Device.ShadowPtrMap.end()) {
-        // create shadow pointers for this entry
+      // If this pointer is not in the map we need to insert it. If the map
+      // contains a stale entry, we need to update it (e.g. if the pointee was
+      // deallocated and later on is reallocated at another device address). The
+      // latter scenario is the subject of LIT test env/base_ptr_ref_count.c. An
+      // entry is removed from ShadowPtrMap only when the PTR of a PTR_AND_OBJ
+      // pair is deallocated, not when the OBJ is deallocated. In
+      // env/base_ptr_ref_count.c the PTR is a global "declare target" pointer,
+      // so it stays in the map for the lifetime of the application. When the
+      // OBJ is deallocated and later on allocated again (at a 
diff erent device
+      // address), ShadowPtrMap still contains an entry for Pointer_HstPtrBegin
+      // which is stale, pointing to the old ExpectedTgtPtrBase of the OBJ.
+      if (Entry == Device.ShadowPtrMap.end() ||
+          Entry->second.TgtPtrVal != ExpectedTgtPtrBase) {
+        // create or update shadow pointers for this entry
         Device.ShadowPtrMap[Pointer_HstPtrBegin] = {
             HstPtrBase, PointerTgtPtrBegin, ExpectedTgtPtrBase};
         UpdateDevPtr = true;