[Attributor] Use Alias Analysis in noalias callsite argument deduction

[uenoku]

Summary

This patch adds a check of alias analysis in noalias callsite argument deduction.

[jdoerfert]

I like this, two comments though.

llvm/lib/Transforms/IPO/Attributor.cpp

1766 ↗

(On Diff #220275)

Hoist this as far out as possible.

llvm/test/Transforms/FunctionAttrs/noalias_returned.ll

266 ↗

(On Diff #220275)

Why didn't this get resolved?

[uenoku]

llvm/test/Transforms/FunctionAttrs/noalias_returned.ll

266 ↗

(On Diff #220275)

This is because, for now, we check noalias for the floating value firsthand:

// (i) Check whether noalias holds in the definition.

    auto &NoAliasAA = A.getAAFor<AANoAlias>(*this, IRP);

    if (!NoAliasAA.isAssumedNoAlias())
      return indicatePessimisticFixpoint();

And GEP is not looked in AANoaliasFloaitingValue so A_0 and B_0 can't be deduced in this point.
I think it is too conservative but without this, at least global variable might be deduced as noalias in the current implementation.

[jdoerfert]

Can you hoist the AAR definition and then this LGTM.

llvm/test/Transforms/FunctionAttrs/noalias_returned.ll

266 ↗

(On Diff #220275)

I see. We need to strip the pointer in the float AANoAlias deduction later.

[uenoku]

Hoist

llvm/trunk/lib/Transforms/IPO/Attributor.cpp

ChangeStatus updateImpl(Attributor &A) override {
     ImmutableCallSite ICS(&getAnchorValue());
     for (unsigned i = 0; i < ICS.getNumArgOperands(); i++) {
       if (getArgNo() == (int)i)
         continue;
       const Value *ArgOp = ICS.getArgOperand(i);
       if (!ArgOp->getType()->isPointerTy())
         continue;
 
-      // TODO: Use AliasAnalysis
-      //       AAResults& AAR = ..;
-      //       if(AAR.isNoAlias(&getAssociatedValue(), ArgOp))
-      //          return indicatePessimitisicFixpoint();
+      if (const Function *F = getAnchorScope()) {
+        if (AAResults *AAR = A.getInfoCache().getAAResultsForFunction(*F)) {
+          LLVM_DEBUG(dbgs()
+                     << "[Attributor][NoAliasCSArg] Check alias between "
+                        "callsite arguments "
+                     << AAR->isNoAlias(&getAssociatedValue(), ArgOp) << " "
+                     << getAssociatedValue() << " " << *ArgOp << "\n");
 
+          if (AAR->isNoAlias(&getAssociatedValue(), ArgOp))
+            continue;
+        }
+      }
       return indicatePessimisticFixpoint();
     }
 
     return ChangeStatus::UNCHANGED;
   }
 
   /// See AbstractAttribute::trackStatistics()
   void trackStatistics() const override { STATS_DECLTRACK_CSARG_ATTR(noalias) }

llvm/trunk/test/Transforms/FunctionAttrs/internal-noalias.ll

-; RUN: opt -S -attributor -attributor-disable=false -attributor-max-iterations-verify -attributor-max-iterations=6 < %s | FileCheck %s
+; RUN: opt -S -passes=attributor -aa-pipeline='basic-aa' -attributor-disable=false -attributor-max-iterations-verify -attributor-max-iterations=6 < %s | FileCheck %s
 
 define dso_local i32 @visible(i32* noalias %A, i32* noalias %B) #0 {
 entry:
   %call1 = call i32 @noalias_args(i32* %A, i32* %B)
   %call2 = call i32 @noalias_args_argmem(i32* %A, i32* %B)
   %add = add nsw i32 %call1, %call2
   ret i32 %add
 }
 
 ; FIXME: Should be something like this.
 ; define internal i32 @noalias_args(i32* nocapture readonly %A, i32* noalias nocapture readonly %B)
-; CHECK: define internal i32 @noalias_args(i32* nocapture %A, i32* nocapture %B)
+; CHECK: define internal i32 @noalias_args(i32* nocapture %A, i32* noalias nocapture %B)
 
 define internal i32 @noalias_args(i32* %A, i32* %B) #0 {
 entry:
   %0 = load i32, i32* %A, align 4
   %1 = load i32, i32* %B, align 4
   %add = add nsw i32 %0, %1
   %call = call i32 @noalias_args_argmem(i32* %A, i32* %B)
   %add2 = add nsw i32 %add, %call

llvm/trunk/test/Transforms/FunctionAttrs/noalias_returned.ll

-; RUN: opt -S -attributor -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=5 < %s | FileCheck %s
 
 ; TEST 1 - negative.
 
 ; void *G;
 ; void *foo(){
 ;   void *V = malloc(4);
 ;   G = V;
 ;   return V;

 declare void @use_nocapture(i8* nocapture)
 declare void @use(i8*)
 define void @test12_1() {
 ; CHECK-LABEL: @test12_1(
 ; CHECK-NEXT:    [[A:%.*]] = alloca i8, align 4
 ; CHECK-NEXT:    [[B:%.*]] = tail call noalias i8* @malloc(i64 4)
 ; CHECK-NEXT:    tail call void @use_nocapture(i8* noalias nonnull align 4 dereferenceable(1) [[A]])
 ; CHECK-NEXT:    tail call void @use_nocapture(i8* noalias nonnull align 4 dereferenceable(1) [[A]])
-; CHECK-NEXT:    tail call void @use_nocapture(i8* noalias [[B]])
+; CHECK-NEXT:    tail call void @use_nocapture(i8* noalias nocapture [[B]])
 ; CHECK-NEXT:    tail call void @use_nocapture(i8* noalias [[B]])
 ; CHECK-NEXT:    ret void
 ;
   %A = alloca i8, align 4
   %B = tail call noalias i8* @malloc(i64 4)
   tail call void @use_nocapture(i8* %A)
   tail call void @use_nocapture(i8* %A)
   tail call void @use_nocapture(i8* %B)
   tail call void @use_nocapture(i8* %B)
   ret void
 }
 
 define void @test12_2(){
 ; CHECK-LABEL: @test12_2(
 ; CHECK-NEXT:    [[A:%.*]] = tail call noalias i8* @malloc(i64 4)
 ; FIXME: This should be @use_nocapture(i8* noalias [[A]])
-; CHECK-NEXT:    tail call void @use_nocapture(i8* [[A]])
+; CHECK-NEXT:    tail call void @use_nocapture(i8* nocapture [[A]])
 ; FIXME: This should be @use_nocapture(i8* noalias [[A]])
 ; CHECK-NEXT:    tail call void @use_nocapture(i8* [[A]])
 ; CHECK-NEXT:    tail call void @use(i8* [[A]])
 ; CHECK-NEXT:    tail call void @use_nocapture(i8* [[A]])
 ; CHECK-NEXT:    ret void
 ;
   %A = tail call noalias i8* @malloc(i64 4)
   tail call void @use_nocapture(i8* %A)
   tail call void @use_nocapture(i8* %A)
   tail call void @use(i8* %A)
   tail call void @use_nocapture(i8* %A)
   ret void
 }
 
 declare void @two_args(i8* nocapture , i8* nocapture)
 define void @test12_3(){
 ; CHECK-LABEL: @test12_3(
   %A = tail call noalias i8* @malloc(i64 4)
-; CHECK: tail call void @two_args(i8* %A, i8* %A)
+; CHECK: tail call void @two_args(i8* nocapture %A, i8* %A)
   tail call void @two_args(i8* %A, i8* %A)
   ret void
 }
 
 define void @test12_4(){
 ; CHECK-LABEL: @test12_4(
   %A = tail call noalias i8* @malloc(i64 4)
   %B = tail call noalias i8* @malloc(i64 4)
   %A_0 = getelementptr i8, i8* %A, i64 0
   %A_1 = getelementptr i8, i8* %A, i64 1
   %B_0 = getelementptr i8, i8* %B, i64 0
 
-; FIXME: This should be @two_args(i8* noalias %A, i8* noalias %B)
-; CHECK: tail call void @two_args(i8* %A, i8* %B)
+; CHECK: tail call void @two_args(i8* noalias %A, i8* noalias %B)
   tail call void @two_args(i8* %A, i8* %B)
 
-; CHECK: tail call void @two_args(i8* %A, i8* %A_0)
+; CHECK: tail call void @two_args(i8* %A, i8* nocapture %A_0)
   tail call void @two_args(i8* %A, i8* %A_0)
 
 ; CHECK: tail call void @two_args(i8* %A, i8* %A_1)
   tail call void @two_args(i8* %A, i8* %A_1)
 
 ; FIXME: This should be @two_args(i8* noalias %A_0, i8* noalias %B_0)
-; CHECK: tail call void @two_args(i8* %A_0, i8* %B_0)
+; CHECK: tail call void @two_args(i8* %A_0, i8* nocapture %B_0)
   tail call void @two_args(i8* %A_0, i8* %B_0)
   ret void
 }