[PATCH] D100551: [deref] No need to check nosync in addition to nofree

[Max Kazantsev via Phabricator via llvm-commits]

mkazantsev created this revision.
mkazantsev added reviewers: reames, nlopes, nikic.
Herald added subscribers: dexonsmith, hiraditya.
mkazantsev requested review of this revision.
Herald added a project: LLVM.
Herald added a subscriber: llvm-commits.

The attribute `nofree` guarantees that a function cannot free memory
by any means, directly or indirectly. If it is specified, there is no need to
check `nosync` separately because it imposes extra limitations (for example,
a function can sync but never write or free memory).

This was already discussed in D99135 <https://reviews.llvm.org/D99135>, but the discussion doesn't explain
case of synching readonly/nofree function.


https://reviews.llvm.org/D100551

Files:
  llvm/lib/IR/Value.cpp
  llvm/test/Analysis/ValueTracking/memory-dereferenceable.ll


Index: llvm/test/Analysis/ValueTracking/memory-dereferenceable.ll
===================================================================
--- llvm/test/Analysis/ValueTracking/memory-dereferenceable.ll
+++ llvm/test/Analysis/ValueTracking/memory-dereferenceable.ll
@@ -261,8 +261,7 @@
 
 ; CHECK-LABEL: 'infer_func_attrs2'
 ; GLOBAL: %p
-; POINT-NOT: %p
-; FIXME: Can be inferred from attributes
+; POINT: %p
 define void @infer_func_attrs2(i32* dereferenceable(8) %p) readonly {
   call void @mayfree()
   %v = load i32, i32* %p
Index: llvm/lib/IR/Value.cpp
===================================================================
--- llvm/lib/IR/Value.cpp
+++ llvm/lib/IR/Value.cpp
@@ -749,10 +749,9 @@
   if (!F)
     return true;
 
-  // A pointer to an object in a function which neither frees, nor can arrange
-  // for another thread to free on its behalf, can not be freed in the scope
-  // of the function.
-  if (F->doesNotFreeMemory() && F->hasNoSync())
+  // A pointer to an object in a function which doesn't free memory, directly
+  // or indirectly (e.g. via creation of other threads that do it).
+  if (F->doesNotFreeMemory())
     return false;
 
   // With garbage collection, deallocation typically occurs solely at or after


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D100551.337722.patch
Type: text/x-patch
Size: 1236 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20210415/e53e1434/attachment.bin>