From 0cdece438972f4c670973d99d2c7743ab822de1a Mon Sep 17 00:00:00 2001
From: Dan Gohman <gohman@apple.com>
Date: Thu, 19 Jan 2012 19:14:36 +0000
Subject: [PATCH] Set the "tail" flag on pattern-matched objc_storeStrong
 calls. rdar://10531041.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@148490 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Transforms/Scalar/ObjCARC.cpp             | 32 +++++++++++++++++++
 .../ObjCARC/contract-storestrong-ivar.ll      |  2 +-
 .../ObjCARC/contract-storestrong.ll           |  2 +-
 3 files changed, 34 insertions(+), 2 deletions(-)

diff --git a/lib/Transforms/Scalar/ObjCARC.cpp b/lib/Transforms/Scalar/ObjCARC.cpp
index 410f6bcd42f..08bb67eb1a2 100644
--- a/lib/Transforms/Scalar/ObjCARC.cpp
+++ b/lib/Transforms/Scalar/ObjCARC.cpp
@@ -3600,6 +3600,11 @@ namespace {
     /// RetainRV calls to make the optimization work on targets which need it.
     const MDString *RetainRVMarker;
 
+    /// StoreStrongCalls - The set of inserted objc_storeStrong calls. If
+    /// at the end of walking the function we have found no alloca
+    /// instructions, these calls can be marked "tail".
+    DenseSet<CallInst *> StoreStrongCalls;
+
     Constant *getStoreStrongCallee(Module *M);
     Constant *getRetainAutoreleaseCallee(Module *M);
     Constant *getRetainAutoreleaseRVCallee(Module *M);
@@ -3803,6 +3808,11 @@ void ObjCARCContract::ContractRelease(Instruction *Release,
   StoreStrong->setDoesNotThrow();
   StoreStrong->setDebugLoc(Store->getDebugLoc());
 
+  // We can't set the tail flag yet, because we haven't yet determined
+  // whether there are any escaping allocas. Remember this call, so that
+  // we can set the tail flag once we know it's safe.
+  StoreStrongCalls.insert(StoreStrong);
+
   if (&*Iter == Store) ++Iter;
   Store->eraseFromParent();
   Release->eraseFromParent();
@@ -3849,6 +3859,13 @@ bool ObjCARCContract::runOnFunction(Function &F) {
 
   PA.setAA(&getAnalysis<AliasAnalysis>());
 
+  // Track whether it's ok to mark objc_storeStrong calls with the "tail"
+  // keyword. Be conservative if the function has variadic arguments.
+  // It seems that functions which "return twice" are also unsafe for the
+  // "tail" argument, because they are setjmp, which could need to
+  // return to an earlier stack state.
+  bool TailOkForStoreStrongs = !F.isVarArg() && !F.callsFunctionThatReturnsTwice();
+
   // For ObjC library calls which return their argument, replace uses of the
   // argument with uses of the call return value, if it dominates the use. This
   // reduces register pressure.
@@ -3905,6 +3922,13 @@ bool ObjCARCContract::runOnFunction(Function &F) {
     case IC_Release:
       ContractRelease(Inst, I);
       continue;
+    case IC_User:
+      // Be conservative if the function has any alloca instructions.
+      // Technically we only care about escaping alloca instructions,
+      // but this is sufficient to handle some interesting cases.
+      if (isa<AllocaInst>(Inst))
+        TailOkForStoreStrongs = false;
+      continue;
     default:
       continue;
     }
@@ -3969,5 +3993,13 @@ bool ObjCARCContract::runOnFunction(Function &F) {
     }
   }
 
+  // If this function has no escaping allocas or suspicious vararg usage,
+  // objc_storeStrong calls can be marked with the "tail" keyword.
+  if (TailOkForStoreStrongs)
+    for (DenseSet<CallInst *>::iterator I = StoreStrongCalls.begin(),
+         E = StoreStrongCalls.end(); I != E; ++I)
+      (*I)->setTailCall();
+  StoreStrongCalls.clear();
+
   return Changed;
 }
diff --git a/test/Transforms/ObjCARC/contract-storestrong-ivar.ll b/test/Transforms/ObjCARC/contract-storestrong-ivar.ll
index 4ad78e75347..4a9b3140f10 100644
--- a/test/Transforms/ObjCARC/contract-storestrong-ivar.ll
+++ b/test/Transforms/ObjCARC/contract-storestrong-ivar.ll
@@ -1,6 +1,6 @@
 ; RUN: opt -objc-arc-contract -S < %s | FileCheck %s
 
-; CHECK: call void @objc_storeStrong(i8**
+; CHECK: tail call void @objc_storeStrong(i8**
 
 target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64"
 target triple = "x86_64-apple-darwin11.0.0"
diff --git a/test/Transforms/ObjCARC/contract-storestrong.ll b/test/Transforms/ObjCARC/contract-storestrong.ll
index fda2ff4cbfc..4ff0596fbbc 100644
--- a/test/Transforms/ObjCARC/contract-storestrong.ll
+++ b/test/Transforms/ObjCARC/contract-storestrong.ll
@@ -9,7 +9,7 @@ declare void @objc_release(i8*)
 
 ; CHECK: define void @test0(
 ; CHECK: entry:
-; CHECK-NEXT: call void @objc_storeStrong(i8** @x, i8* %p) nounwind
+; CHECK-NEXT: tail call void @objc_storeStrong(i8** @x, i8* %p) nounwind
 ; CHECK-NEXT: ret void
 define void @test0(i8* %p) {
 entry: