[ObjC][ARC] Delete ObjC runtime calls on global variables annotated

with 'objc_arc_inert'

Those calls are no-ops, so they can be safely deleted.

rdar://problem/49839633

Differential Revision: https://reviews.llvm.org/D62433

llvm-svn: 363468

2 files changed, 48 insertions, 0 deletions

diff --git a/llvm/lib/Analysis/ObjCARCInstKind.cpp b/llvm/lib/Analysis/ObjCARCInstKind.cpp
index 59994bae8be..0e96c6e975c 100644
--- a/llvm/lib/Analysis/ObjCARCInstKind.cpp
+++ b/llvm/lib/Analysis/ObjCARCInstKind.cpp
@@ -481,6 +481,41 @@ bool llvm::objcarc::IsNoopOnNull(ARCInstKind Class) {
   llvm_unreachable("covered switch isn't covered?");
 }
 
+/// Test if the given class represents instructions which do nothing if
+/// passed a global variable.
+bool llvm::objcarc::IsNoopOnGlobal(ARCInstKind Class) {
+  switch (Class) {
+  case ARCInstKind::Retain:
+  case ARCInstKind::RetainRV:
+  case ARCInstKind::ClaimRV:
+  case ARCInstKind::Release:
+  case ARCInstKind::Autorelease:
+  case ARCInstKind::AutoreleaseRV:
+  case ARCInstKind::RetainBlock:
+  case ARCInstKind::FusedRetainAutorelease:
+  case ARCInstKind::FusedRetainAutoreleaseRV:
+    return true;
+  case ARCInstKind::AutoreleasepoolPush:
+  case ARCInstKind::AutoreleasepoolPop:
+  case ARCInstKind::LoadWeakRetained:
+  case ARCInstKind::StoreWeak:
+  case ARCInstKind::InitWeak:
+  case ARCInstKind::LoadWeak:
+  case ARCInstKind::MoveWeak:
+  case ARCInstKind::CopyWeak:
+  case ARCInstKind::DestroyWeak:
+  case ARCInstKind::StoreStrong:
+  case ARCInstKind::IntrinsicUser:
+  case ARCInstKind::CallOrUser:
+  case ARCInstKind::Call:
+  case ARCInstKind::User:
+  case ARCInstKind::None:
+  case ARCInstKind::NoopCast:
+    return false;
+  }
+  llvm_unreachable("covered switch isn't covered?");
+}
+
 /// Test if the given class represents instructions which are always safe
 /// to mark with the "tail" keyword.
 bool llvm::objcarc::IsAlwaysTail(ARCInstKind Class) {
diff --git a/llvm/lib/Transforms/ObjCARC/ObjCARCOpts.cpp b/llvm/lib/Transforms/ObjCARC/ObjCARCOpts.cpp
index fa30ee6f72b..6653ff0bb91 100644
--- a/llvm/lib/Transforms/ObjCARC/ObjCARCOpts.cpp
+++ b/llvm/lib/Transforms/ObjCARC/ObjCARCOpts.cpp
@@ -760,6 +760,19 @@ void ObjCARCOpt::OptimizeIndividualCalls(Function &F) {
 
     LLVM_DEBUG(dbgs() << "Visiting: Class: " << Class << "; " << *Inst << "\n");
 
+    // Some of the ARC calls can be deleted if their arguments are global
+    // variables that are inert in ARC.
+    if (IsNoopOnGlobal(Class)) {
+      Value *Opnd = Inst->getOperand(0);
+      if (auto *GV = dyn_cast<GlobalVariable>(Opnd->stripPointerCasts()))
+        if (GV->hasAttribute("objc_arc_inert")) {
+          if (!Inst->getType()->isVoidTy())
+            Inst->replaceAllUsesWith(Opnd);
+          Inst->eraseFromParent();
+          continue;
+        }
+    }
+
     switch (Class) {
     default: break;