[Attributor] Implement AANoAliasCallSiteArgument initialization

[uenoku]

Summary

This patch adds an appropriate initialize method for AANoAliasCallSiteArgument.

[jdoerfert]

Small nit, otherwise LGTM.

llvm/lib/Transforms/IPO/Attributor.cpp

1597

can't u just say hasAttr( ? Some of the CallSite getters look at the argument, other do not.

[uenoku]

llvm/lib/Transforms/IPO/Attributor.cpp

1597

I think SubsumingPositionIterator will look at associatedValue when given a callsite arugment. test11 below will fail.

llvm/lib/Transforms/IPO/Attributor.cpp

struct AANoAliasArgument final
   void trackStatistics() const override { STATS_DECLTRACK_ARG_ATTR(noalias) }
 };
 
 struct AANoAliasCallSiteArgument final : AANoAliasImpl {
   AANoAliasCallSiteArgument(const IRPosition &IRP) : AANoAliasImpl(IRP) {}
 
   /// See AbstractAttribute::initialize(...).
   void initialize(Attributor &A) override {
-    // TODO: It isn't sound to initialize as the same with `AANoAliasImpl`
-    // because `noalias` may not be valid in the current position.
+    // See callsite argument attribute and callee argument attribute.
+    ImmutableCallSite ICS(&getAnchorValue());
+    if (ICS.paramHasAttr(getArgNo(), Attribute::NoAlias))
+      indicateOptimisticFixpoint();
   }
 
   /// See AbstractAttribute::updateImpl(...).
   ChangeStatus updateImpl(Attributor &A) override {
     // TODO: Implement this.
     return indicatePessimisticFixpoint();
   }
 

llvm/test/Transforms/FunctionAttrs/noalias_returned.ll

 
 5:                                                ; preds = %1, %4
   ret i8* %2
 }
 
 ; TEST 9
 ; Simple Argument Test
 define internal void @test9(i8* %a, i8* %b) {
-; FIXME: missing noalias
-; CHECK: define internal void @test9(i8* %a, i8* %b)
+; CHECK: define internal void @test9(i8* noalias %a, i8* %b)
   ret void
 }
 define void @test9_helper(i8* %a, i8* %b) {
   tail call void @test9(i8* noalias %a, i8* %b)
   tail call void @test9(i8* noalias %b, i8* noalias %a)
   ret void
 }
 
 
 ; TEST 10
 ; Simple CallSite Test
 
-declare void @test10_helper(i8* %a)
+declare void @test10_helper_1(i8* %a)
+define void @test10_helper_2(i8* noalias %a) {
+  ret void
+}
 define void @test10(i8* noalias %a) {
 ; CHECK: define void @test10(i8* noalias %a)
 ; FIXME: missing noalias
-; CHECK-NEXT:   tail call void @test10_helper(i8* %a)
-  tail call void @test10_helper(i8* %a)
+; CHECK-NEXT:   tail call void @test10_helper_1(i8* %a)
+  tail call void @test10_helper_1(i8* %a)
+
+; CHECK-NEXT:   tail call void @test10_helper_2(i8* noalias %a)
+  tail call void @test10_helper_2(i8* %a)
   ret void
 }
 
 ; TEST 11
 ; CallSite Test
 
 declare void @test11_helper(i8* %a, i8 *%b)
 define void @test11(i8* noalias %a) {
 ; CHECK: define void @test11(i8* noalias %a)
 ; CHECK-NEXT:   tail call void @test11_helper(i8* %a, i8* %a)
   tail call void @test11_helper(i8* %a, i8* %a)
   ret void
 }