[Attributor] Shortcut no-return through will-return

No-return and will-return are exclusive, assuming the latter is more
prominent we can avoid updates of the former unless will-return is not
known for sure.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@374739 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/IPO/Attributor.cpp

@@ -2859,6 +2859,14 @@ struct AAAlignCallSiteReturned final : AAAlignImpl {
 struct AANoReturnImpl : public AANoReturn {
   AANoReturnImpl(const IRPosition &IRP) : AANoReturn(IRP) {}
 
+  /// See AbstractAttribute::initialize(...).
+  void initialize(Attributor &A) override {
+    AANoReturn::initialize(A);
+    Function *F = getAssociatedFunction();
+    if (!F || F->hasFnAttribute(Attribute::WillReturn))
+      indicatePessimisticFixpoint();
+  }
+
   /// See AbstractAttribute::getAsStr().
   const std::string getAsStr() const override {
     return getAssumed() ? "noreturn" : "may-return";
@@ -2866,6 +2874,9 @@ struct AANoReturnImpl : public AANoReturn {
 
   /// See AbstractAttribute::updateImpl(Attributor &A).
   virtual ChangeStatus updateImpl(Attributor &A) override {
+    const auto &WillReturnAA = A.getAAFor<AAWillReturn>(*this, getIRPosition());
+    if (WillReturnAA.isKnownWillReturn())
+      return indicatePessimisticFixpoint();
     auto CheckForNoReturn = [](Instruction &) { return false; };
     if (!A.checkForAllInstructions(CheckForNoReturn, *this,
                                    {(unsigned)Instruction::Ret}))
@@ -2885,14 +2896,6 @@ struct AANoReturnFunction final : AANoReturnImpl {
 struct AANoReturnCallSite final : AANoReturnImpl {
   AANoReturnCallSite(const IRPosition &IRP) : AANoReturnImpl(IRP) {}
 
-  /// See AbstractAttribute::initialize(...).
-  void initialize(Attributor &A) override {
-    AANoReturnImpl::initialize(A);
-    Function *F = getAssociatedFunction();
-    if (!F)
-      indicatePessimisticFixpoint();
-  }
-
   /// See AbstractAttribute::updateImpl(...).
   ChangeStatus updateImpl(Attributor &A) override {
     // TODO: Once we have call site specific value information we can provide

test/Transforms/FunctionAttrs/fn_noreturn.ll

@@ -1,4 +1,4 @@
-; RUN: opt -functionattrs -attributor -attributor-disable=false -attributor-max-iterations-verify -attributor-max-iterations=2 -S < %s | FileCheck %s
+; RUN: opt -functionattrs -attributor -attributor-disable=false -attributor-max-iterations-verify -attributor-max-iterations=3 -S < %s | FileCheck %s
 ;
 ; Test cases specifically designed for the "no-return" function attribute.
 ; We use FIXME's to indicate problems and missing attributes.
@@ -124,4 +124,16 @@ cond.end:                                         ; preds = %cond.false, %cond.t
   ret i32 %cond
 }
 
+
+; TEST 6: willreturn means *not* no-return
+; CHECK:      Function Attrs: nofree norecurse nosync nounwind readnone willreturn
+; CHECK-NEXT: define i32 @endless_loop_but_willreturn
+define i32 @endless_loop_but_willreturn(i32 %a) willreturn {
+entry:
+  br label %while.body
+
+while.body:                                       ; preds = %entry, %while.body
+  br label %while.body
+}
+
 attributes #0 = { noinline nounwind uwtable }

test/Transforms/FunctionAttrs/internal-noalias.ll

@@ -1,4 +1,4 @@
-; RUN: opt -S -passes=attributor -aa-pipeline='basic-aa' -attributor-disable=false -attributor-max-iterations-verify -attributor-max-iterations=5 < %s | FileCheck %s
+; RUN: opt -S -passes=attributor -aa-pipeline='basic-aa' -attributor-disable=false -attributor-max-iterations-verify -attributor-max-iterations=3 < %s | FileCheck %s
 
 define dso_local i32 @visible(i32* noalias %A, i32* noalias %B) #0 {
 entry:

test/Transforms/FunctionAttrs/liveness.ll

@@ -1,4 +1,4 @@
-; RUN: opt -attributor --attributor-disable=false -attributor-max-iterations-verify -attributor-max-iterations=2 -S < %s | FileCheck %s
+; RUN: opt -attributor --attributor-disable=false -attributor-max-iterations-verify -attributor-max-iterations=3 -S < %s | FileCheck %s
 
 declare void @no_return_call() nofree noreturn nounwind readnone
 

test/Transforms/FunctionAttrs/norecurse.ll

@@ -1,6 +1,6 @@
 ; RUN: opt < %s -basicaa -functionattrs -rpo-functionattrs -S | FileCheck %s --check-prefixes=CHECK,BOTH
 ; RUN: opt < %s -aa-pipeline=basic-aa -passes='cgscc(function-attrs),rpo-functionattrs' -S | FileCheck %s --check-prefixes=CHECK,BOTH
-; RUN: opt -passes=attributor --attributor-disable=false -attributor-max-iterations-verify -attributor-max-iterations=2 -S < %s | FileCheck %s --check-prefixes=ATTRIBUTOR,BOTH
+; RUN: opt -passes=attributor --attributor-disable=false -attributor-max-iterations-verify -attributor-max-iterations=4 -S < %s | FileCheck %s --check-prefixes=ATTRIBUTOR,BOTH
 
 ; CHECK: Function Attrs
 ; CHECK-SAME: norecurse nounwind readnone

test/Transforms/FunctionAttrs/noreturn_async.ll

@@ -1,4 +1,4 @@
-; RUN: opt -functionattrs -attributor -attributor-disable=false -attributor-max-iterations-verify -attributor-max-iterations=2 -S < %s | FileCheck %s
+; RUN: opt -functionattrs -attributor -attributor-disable=false -attributor-max-iterations-verify -attributor-max-iterations=3 -S < %s | FileCheck %s
 ;
 ; This file is the same as noreturn_sync.ll but with a personality which
 ; indicates that the exception handler *can* catch asynchronous exceptions. As

test/Transforms/FunctionAttrs/noreturn_sync.ll

@@ -1,4 +1,4 @@
-; RUN: opt -functionattrs -attributor -attributor-disable=false -attributor-max-iterations-verify -attributor-max-iterations=2 -S < %s | FileCheck %s
+; RUN: opt -functionattrs -attributor -attributor-disable=false -attributor-max-iterations-verify -attributor-max-iterations=3 -S < %s | FileCheck %s
 ;
 ; This file is the same as noreturn_async.ll but with a personality which
 ; indicates that the exception handler *cannot* catch asynchronous exceptions.