[objc-arc] Introduce the concept of RCIdentity and rename all relevant functions to use that name. NFC.

The RCIdentity root ("Reference Count Identity Root") of a value V is a
dominating value U for which retaining or releasing U is equivalent to
retaining or releasing V. In other words, ARC operations on V are
equivalent to ARC operations on U.

This is a useful property to ascertain since we can use this in the ARC
optimizer to make it easier to match up ARC operations by always mapping
ARC operations to RCIdentityRoots instead of pointers themselves. Then
we perform pairing of retains, releases which are applied to the same
RCIdentityRoot.

In general, the two ways that we see RCIdentical values in ObjC are via:

  1. PointerCasts
  2. Forwarding Calls that return their argument verbatim.

As such in ObjC, two RCIdentical pointers must always point to the same
memory location.

Previously this concept was implicit in the code and various methods
that dealt with this concept were given functional names that did not
conform to any name in the "ARC" model. This often times resulted in
code that was hard for the non-ARC acquanted to understand resulting in
unhappiness and confusion.

llvm-svn: 229796

1 files changed, 2 insertions, 2 deletions

diff --git a/llvm/lib/Transforms/ObjCARC/DependencyAnalysis.cpp b/llvm/lib/Transforms/ObjCARC/DependencyAnalysis.cpp
index f6c236c31ef..9160493212a 100644
--- a/llvm/lib/Transforms/ObjCARC/DependencyAnalysis.cpp
+++ b/llvm/lib/Transforms/ObjCARC/DependencyAnalysis.cpp
@@ -171,7 +171,7 @@ llvm::objcarc::Depends(DependenceKind Flavor, Instruction *Inst,
     case IC_Retain:
     case IC_RetainRV:
       // Check for a retain of the same pointer for merging.
-      return GetObjCArg(Inst) == Arg;
+      return GetArgRCIdentityRoot(Inst) == Arg;
     default:
       // Nothing else matters for objc_retainAutorelease formation.
       return false;
@@ -183,7 +183,7 @@ llvm::objcarc::Depends(DependenceKind Flavor, Instruction *Inst,
     case IC_Retain:
     case IC_RetainRV:
       // Check for a retain of the same pointer for merging.
-      return GetObjCArg(Inst) == Arg;
+      return GetArgRCIdentityRoot(Inst) == Arg;
     default:
       // Anything that can autorelease interrupts
       // retainAutoreleaseReturnValue formation.