[Attributor][FIX] HasBeenWrittenTo logic should only be used for reads

If we look at a write, we should not enact the "has been written to"
logic introduced to avoid spurious write -> read dependences. Doing so
lead to elimination of stores we needed, which is obviously bad.

llvm/lib/Transforms/IPO/AttributorAttributes.cpp

@@ -1069,7 +1069,7 @@ struct AAPointerInfoImpl
       bool Dominates = DT && Exact && Acc.isMustAccess() &&
                        (Acc.getLocalInst()->getFunction() == &Scope) &&
                        DT->dominates(Acc.getRemoteInst(), &I);
-      if (Dominates)
+      if (FindInterferingWrites && Dominates)
         HasBeenWrittenTo = true;
 
       // For now we only filter accesses based on CFG reasoning which does not

llvm/test/Transforms/Attributor/value-simplify-pointer-info.ll

@@ -2674,6 +2674,7 @@ define i32 @static_global_not_simplifiable_2(i32 %cnd) {
 ; IS__TUNIT_NPM-NEXT:    store i32 1, i32* @Flag4, align 4, !tbaa [[TBAA3]]
 ; IS__TUNIT_NPM-NEXT:    call void @sync() #[[ATTR14:[0-9]+]]
 ; IS__TUNIT_NPM-NEXT:    [[I:%.*]] = load i32, i32* @Flag4, align 4, !tbaa [[TBAA3]]
+; IS__TUNIT_NPM-NEXT:    store i32 2, i32* @Flag4, align 4, !tbaa [[TBAA3]]
 ; IS__TUNIT_NPM-NEXT:    ret i32 [[I]]
 ;
 ; IS__CGSCC_OPM-LABEL: define {{[^@]+}}@static_global_not_simplifiable_2
@@ -2691,6 +2692,7 @@ define i32 @static_global_not_simplifiable_2(i32 %cnd) {
 ; IS__CGSCC_NPM-NEXT:    store i32 1, i32* @Flag4, align 4, !tbaa [[TBAA3]]
 ; IS__CGSCC_NPM-NEXT:    call void @sync() #[[ATTR16:[0-9]+]]
 ; IS__CGSCC_NPM-NEXT:    [[I:%.*]] = load i32, i32* @Flag4, align 4, !tbaa [[TBAA3]]
+; IS__CGSCC_NPM-NEXT:    store i32 2, i32* @Flag4, align 4, !tbaa [[TBAA3]]
 ; IS__CGSCC_NPM-NEXT:    ret i32 [[I]]
 ;
 entry: