[ObjC] Override TailCallKind when lowering objc intrinsics

[thegameg]

Summary

The tail-call-kind-ness is known by the ObjCARC analysis and can be enforced while lowering the intrinsics to calls.

This allows us to get the requested tail calls at -O0 without trying to preserve the attributes throughout passes that change code even at -O0 ,like the Always Inliner, where the ObjCOpt pass doesn't run.

[thegameg]

Remove useless #include.

[rjmccall]

LGTM

llvm/lib/CodeGen/PreISelIntrinsicLowering.cpp

61

"whether"

llvm/lib/CodeGen/PreISelIntrinsicLowering.cpp

 //===- PreISelIntrinsicLowering.cpp - Pre-ISel intrinsic lowering pass ----===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 //
 // This pass implements IR lowering for the llvm.load.relative and llvm.objc.*
 // intrinsics.
 //
 //===----------------------------------------------------------------------===//
 
 #include "llvm/CodeGen/PreISelIntrinsicLowering.h"
+#include "llvm/Analysis/ObjCARCInstKind.h"
 #include "llvm/CodeGen/Passes.h"
 #include "llvm/IR/Function.h"
 #include "llvm/IR/Intrinsics.h"
 #include "llvm/IR/IRBuilder.h"
 #include "llvm/IR/Instructions.h"
 #include "llvm/IR/Module.h"
 #include "llvm/IR/Type.h"
 #include "llvm/IR/User.h"
for (auto I = F.use_begin(), E = F.use_end(); I != E;) {
     CI->replaceAllUsesWith(ResultPtr);
     CI->eraseFromParent();
     Changed = true;
   }
 
   return Changed;
 }
 
+// ObjCARC has knowledge about whether an obj-c runtime function needs to be
+// always tail-called or never tail-called.
+static CallInst::TailCallKind getOverridingTailCallKind(const Function &F) {
+  objcarc::ARCInstKind Kind = objcarc::GetFunctionClass(&F);
+  if (objcarc::IsAlwaysTail(Kind))
+    return CallInst::TCK_Tail;
+  else if (objcarc::IsNeverTail(Kind))
+    return CallInst::TCK_NoTail;
+  return CallInst::TCK_None;
+}
+
 static bool lowerObjCCall(Function &F, const char *NewFn,
                           bool setNonLazyBind = false) {
   if (F.use_empty())
     return false;
 
   // If we haven't already looked up this function, check to see if the
   // program already contains a function with this name.
   Module *M = F.getParent();
   FunctionCallee FCache = M->getOrInsertFunction(NewFn, F.getFunctionType());
 
   if (Function *Fn = dyn_cast<Function>(FCache.getCallee())) {
     Fn->setLinkage(F.getLinkage());
     if (setNonLazyBind && !Fn->isWeakForLinker()) {
       // If we have Native ARC, set nonlazybind attribute for these APIs for
       // performance.
       Fn->addFnAttr(Attribute::NonLazyBind);
     }
   }
 
+  CallInst::TailCallKind OverridingTCK = getOverridingTailCallKind(F);
+
   for (auto I = F.use_begin(), E = F.use_end(); I != E;) {
     auto *CI = cast<CallInst>(I->getUser());
     assert(CI->getCalledFunction() && "Cannot lower an indirect call!");
     ++I;
 
     IRBuilder<> Builder(CI->getParent(), CI->getIterator());
     SmallVector<Value *, 8> Args(CI->arg_begin(), CI->arg_end());
     CallInst *NewCI = Builder.CreateCall(FCache, Args);
     NewCI->setName(CI->getName());
-    NewCI->setTailCallKind(CI->getTailCallKind());
+
+    // Try to set the most appropriate TailCallKind based on both the current
+    // attributes and the ones that we could get from ObjCARC's special
+    // knowledge of the runtime functions.
+    //
+    // std::max respects both requirements of notail and tail here:
+    // * notail on either the call or from ObjCARC becomes notail
+    // * tail on either side is stronger than none, but not notail
+    CallInst::TailCallKind TCK = CI->getTailCallKind();
+    NewCI->setTailCallKind(std::max(TCK, OverridingTCK));
+
     if (!CI->use_empty())
       CI->replaceAllUsesWith(NewCI);
     CI->eraseFromParent();
   }
 
   return true;
 }
 

llvm/test/Transforms/PreISelIntrinsicLowering/objc-arc.ll

 ; RUN: opt -pre-isel-intrinsic-lowering -S -o - %s | FileCheck %s
 ; RUN: opt -passes='pre-isel-intrinsic-lowering' -S -o - %s | FileCheck %s
 
 ; Make sure calls to the objc intrinsics are translated to calls in to the
 ; runtime
 
 define i8* @test_objc_autorelease(i8* %arg0) {
 ; CHECK-LABEL: test_objc_autorelease
 ; CHECK-NEXT: entry
-; CHECK-NEXT: %0 = call i8* @objc_autorelease(i8* %arg0)
+; CHECK-NEXT: %0 = notail call i8* @objc_autorelease(i8* %arg0)
 ; CHECK-NEXT: ret i8* %0
 entry:
   %0 = call i8* @llvm.objc.autorelease(i8* %arg0)
   ret i8* %0
 }
 
 define void @test_objc_autoreleasePoolPop(i8* %arg0) {
 ; CHECK-LABEL: test_objc_autoreleasePoolPop

 entry:
   %0 = call i8* @llvm.objc.autoreleasePoolPush()
   ret i8* %0
 }
 
 define i8* @test_objc_autoreleaseReturnValue(i8* %arg0) {
 ; CHECK-LABEL: test_objc_autoreleaseReturnValue
 ; CHECK-NEXT: entry
-; CHECK-NEXT: %0 = call i8* @objc_autoreleaseReturnValue(i8* %arg0)
+; CHECK-NEXT: %0 = tail call i8* @objc_autoreleaseReturnValue(i8* %arg0)
 ; CHECK-NEXT: ret i8* %0
 entry:
   %0 = call i8* @llvm.objc.autoreleaseReturnValue(i8* %arg0)
   ret i8* %0
 }
 
 define void @test_objc_copyWeak(i8** %arg0, i8** %arg1) {
 ; CHECK-LABEL: test_objc_copyWeak

 entry:
   call void @llvm.objc.release(i8* %arg0)
   ret void
 }
 
 define i8* @test_objc_retain(i8* %arg0) {
 ; CHECK-LABEL: test_objc_retain
 ; CHECK-NEXT: entry
-; CHECK-NEXT: %0 = call i8* @objc_retain(i8* %arg0)
+; CHECK-NEXT: %0 = tail call i8* @objc_retain(i8* %arg0)
 ; CHECK-NEXT: ret i8* %0
 entry:
   %0 = call i8* @llvm.objc.retain(i8* %arg0)
   ret i8* %0
 }
 
 define i8* @test_objc_retainAutorelease(i8* %arg0) {
 ; CHECK-LABEL: test_objc_retainAutorelease

 entry:
   %0 = tail call i8* @llvm.objc.retainAutoreleaseReturnValue(i8* %arg0)
   ret i8* %0
 }
 
 define i8* @test_objc_retainAutoreleasedReturnValue(i8* %arg0) {
 ; CHECK-LABEL: test_objc_retainAutoreleasedReturnValue
 ; CHECK-NEXT: entry
-; CHECK-NEXT: %0 = call i8* @objc_retainAutoreleasedReturnValue(i8* %arg0)
+; CHECK-NEXT: %0 = tail call i8* @objc_retainAutoreleasedReturnValue(i8* %arg0)
 ; CHECK-NEXT: ret i8* %0
 entry:
   %0 = call i8* @llvm.objc.retainAutoreleasedReturnValue(i8* %arg0)
   ret i8* %0
 }
 
 define i8* @test_objc_retainBlock(i8* %arg0) {
 ; CHECK-LABEL: test_objc_retainBlock

 entry:
   %0 = call i8* @llvm.objc.storeWeak(i8** %arg0, i8* %arg1)
   ret i8* %0
 }
 
 define i8* @test_objc_unsafeClaimAutoreleasedReturnValue(i8* %arg0) {
 ; CHECK-LABEL: test_objc_unsafeClaimAutoreleasedReturnValue
 ; CHECK-NEXT: entry
-; CHECK-NEXT: %0 = call i8* @objc_unsafeClaimAutoreleasedReturnValue(i8* %arg0)
+; CHECK-NEXT: %0 = tail call i8* @objc_unsafeClaimAutoreleasedReturnValue(i8* %arg0)
 ; CHECK-NEXT: ret i8* %0
 entry:
   %0 = call i8* @llvm.objc.unsafeClaimAutoreleasedReturnValue(i8* %arg0)
   ret i8* %0
 }
 
 define i8* @test_objc_retainedObject(i8* %arg0) {
 ; CHECK-LABEL: test_objc_retainedObject