On Tue, May 12, 2020 at 2:44 PM 易会战 via Gcc <gcc@gcc.gnu.org> wrote: > > hi, I am working on gcc ssa name. For each function, we can traverse all > defined ssa name by macro FOR_EACH_SSA_NAME. If a ssa name is default > definition for a symbol (check SSA_NAME_IS_DEFAULT_DEF) , I can get the > symbol by SSA_NAME_VAR. But for a virtual DEFAULT DEF, I cannot get it, > SSA_NAME_VAR return a identifier named .MEM. I cannot find which variable > related to the default definition. Why and how I should find the related > variable? > > > By the way , I give my current work, I wish find a MEM_REF refer to > global/heap memory or local stack. I try my best to get a correct memory > type. Since MEM_REF have a base address, which is often a ssa name. Athough > it is not virtual ssa name. But I find just check ssa name data flow is not > enough to get the info. > For example, a malloc function allocate some heap memory and record the > address in a global ptr. On gimple ssa IR, the malloc function return a > address assigned to a ssa name , then ssa name assign the value to the global > ptr. When i check ssa name defined by the global ptr, I donot know if the ptr > point to global memory or local memory. > Please see the gimple code: > _2 = malloc() > ptr = _2 > _3 = ptr > MEM_REF[BASE _3] > I wish get _3 is a address pointing to global memory. But just from > _3=ptr, cannot judge it. > I wish memory SSA can help solve the problem.
memory SSA will not solve this problem. You can instead query points-to information on _3 for example by calling ptr_deref_may_alias_global_p (_3) which internally looks at SSA_NAME_PTR_INFO which contains the solution of the points-to computation. Richard. > > Or gcc gives the info at other pass? wish get some advice. Thanks a lot.
