[LoopIdiom] Merge TBAA of adjacent stores when creating memset

Factor in the TBAA of adjacent stores instead of just the head store
when merging stores into a memset. We were seeing GVN remove a load that
had a TBAA that matched the 2nd store because GVN determined it didn't
match the TBAA of the memset. The memset had the TBAA of only the first
store.

i.e. Loading the field pi_ of shared_count after memset to create an
array of shared_ptr

template<class T>
class shared_ptr {
  T *p;
  shared_count refcount;
};

class shared_count {
  sp_counted_base *pi_;
};

Differential Revision: https://reviews.llvm.org/D122205

(cherry picked from commit e02f497)

Author: steplong

llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp

@@ -1173,6 +1173,8 @@ bool LoopIdiomRecognize::processLoopStridedStore(
   CallInst *NewCall;
   if (SplatValue) {
     AAMDNodes AATags = TheStore->getAAMetadata();
+    for (Instruction *Store : Stores)
+      AATags = AATags.merge(Store->getAAMetadata());
     if (auto CI = dyn_cast<ConstantInt>(NumBytes))
       AATags = AATags.extendTo(CI->getZExtValue());
     else

llvm/test/Transforms/LoopIdiom/memset-tbaa.ll

@@ -91,6 +91,45 @@ for.body:
   br i1 %exitcond.not, label %for.cond.cleanup, label %for.body
 }
 
+%struct.A = type { i32*, %struct.B }
+%struct.B = type { i32* }
+
+define dso_local void @adjacent_store_memset(%struct.A* nocapture %a, i64 %len) {
+; CHECK-LABEL: @adjacent_store_memset(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[A1:%.*]] = bitcast %struct.A* [[A:%.*]] to i8*
+; CHECK-NEXT:    [[UMAX:%.*]] = call i64 @llvm.umax.i64(i64 %len, i64 1)
+; CHECK-NEXT:    [[LEN:%.*]] = shl nuw i64 [[UMAX]], 4
+; CHECK-NEXT:    call void @llvm.memset.p0i8.i64(i8* align 8 [[A1]], i8 0, i64 [[LEN]], i1 false), !tbaa [[TBAA9:![0-9]+]]
+; CHECK-NEXT:    br label [[FOR_BODY:%.*]]
+; CHECK:       for.cond.cleanup:
+; CHECK-NEXT:    ret void
+; CHECK:       for.body:
+; CHECK-NEXT:    [[I_09:%.*]] = phi i64 [ [[INC:%.*]], [[FOR_BODY]] ], [ 0, %entry ]
+; CHECK-NEXT:    %p = getelementptr inbounds %struct.A, %struct.A* [[A]], i64 [[I_09]], i32 0
+; CHECK-NEXT:    %p2 = getelementptr inbounds %struct.A, %struct.A* [[A]], i64 [[I_09]], i32 1, i32 0
+; CHECK-NEXT:    [[INC]] = add i64 [[I_09]], 1
+; CHECK-NEXT:    [[EXITCOND_NOT:%.*]] = icmp ult i64 [[INC]], %len
+; CHECK-NEXT:    br i1 [[EXITCOND_NOT]], label [[FOR_BODY]], label [[FOR_COND_CLEANUP_LOOPEXIT:%.*]]
+;
+entry:
+  br label %for.body
+
+for.cond.cleanup:
+  ret void
+
+for.body:
+  %i.09 = phi i64 [ %inc, %for.body ], [ 0, %entry ]
+  %p = getelementptr inbounds %struct.A, %struct.A* %a, i64 %i.09, i32 0
+  store i32* null, i32** %p, align 8, !tbaa !18
+  %p2 = getelementptr inbounds %struct.A, %struct.A* %a, i64 %i.09, i32 1, i32 0
+  store i32* null, i32** %p2, align 8, !tbaa !21
+  %inc = add i64 %i.09, 1
+  %cmp = icmp ult i64 %inc, %len
+  br i1 %cmp, label %for.body, label %for.cond.cleanup
+}
+
+
 ; CHECK: [[TBAA0]] = !{[[TBAA1:.+]], [[TBAA1]], i64 0}
 ; CHECK: [[TBAA1]] = !{!"double", [[TBAA2:.+]], i64 0}
 ; CHECK: [[TBAA2]] = !{!"omnipotent char", [[TBAA3:.+]], i64 0}
@@ -99,6 +138,8 @@ for.body:
 ; CHECK: [[TBAA5]] = !{[[TBAA7:.+]], i64 32, !"_ZTS1A", [[TBAA6]], i64 0, i64 8, [[TBAA6]], i64 8, i64 8, [[TBAA6]], i64 16, i64 8, [[TBAA6]], i64 24, i64 8}
 ; CHECK: [[TBAA7]] = !{[[TBAA3]], i64 0, !"omnipotent char"}
 ; CHECK: [[TBAA6]] = !{[[TBAA7]], i64 8, !"double"}
+; CHECK: [[TBAA9]] = !{[[TBAA10:.+]], [[TBAA10]], i64 0}
+; CHECK: [[TBAA10]] = !{!"any pointer", [[TBAA2]], i64 0}
 
 !5 = !{!6, !6, i64 0}
 !6 = !{!"double", !7, i64 0}
@@ -109,3 +150,9 @@ for.body:
 !17 = !{!15, i64 8, !"double"}
 !9 = !{!15, i64 32, !"_ZTS1A", !17, i64 0, i64 8, !17, i64 8, i64 8, !17, i64 16, i64 8, !17, i64 24, i64 8}
 !10 = !{!9, !17, i64 0, i64 1}
+
+!18 = !{!19, !20, i64 0}
+!19 = !{!"A", !20, i64 0, !22, i64 8}
+!20 = !{!"any pointer", !7, i64 0}
+!21 = !{!22, !20, i64 0}
+!22 = !{!"B", !20, i64 0}