[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

1 files changed, 13 insertions, 0 deletions

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;