[PATCH] D99138: [deref] Infer a few more cases of global dereferenceability in a callee

[Philip Reames via Phabricator via llvm-commits]

reames updated this revision to Diff 333179.
reames added a comment.

Refresh per reviewer preference for attribute handling.

Byval, etc... split to https://reviews.llvm.org/D99310.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D99138/new/

https://reviews.llvm.org/D99138

Files:
  llvm/include/llvm/IR/Function.h
  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
@@ -260,9 +260,7 @@
 }
 
 ; CHECK-LABEL: 'infer_func_attrs2'
-; GLOBAL: %p
-; POINT-NOT: %p
-; FIXME: Can be inferred from attributes
+; CHECK: %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
@@ -750,7 +750,8 @@
 
   // 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.
+  // of the function.  Note that readonly implies both of these.  Which is good
+  // because we don't directly infer nosync, but do readonly.
   if (F->doesNotFreeMemory() && F->hasNoSync())
     return false;
 
Index: llvm/include/llvm/IR/Function.h
===================================================================
--- llvm/include/llvm/IR/Function.h
+++ llvm/include/llvm/IR/Function.h
@@ -626,7 +626,9 @@
 
   /// Determine if the call can synchroize with other threads
   bool hasNoSync() const {
-    return hasFnAttribute(Attribute::NoSync);
+    // Coordination with another thread requires at least one write to shared
+    // memory, so readonly also implies nosync.
+    return onlyReadsMemory() || hasFnAttribute(Attribute::NoSync);
   }
   void setNoSync() {
     addFnAttr(Attribute::NoSync);


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