Hi Chris, On 6 March 2017 at 15:16, Christopher Li <sparse@xxxxxxxxxxx> wrote: > On Sun, Mar 5, 2017 at 7:20 PM, Luc Van Oostenryck > <luc.vanoostenryck@xxxxxxxxx> wrote: >> In sparse, pointer arithmetic and accessing the field >> of a structure or an array is simply done via OP_ADD, >> the offset being calculated at evaluation time. >> On the other hand, LLVM allows addition only on two >> integers and pointer arithmetic/member access is done >> via 'getelementptr'. >> >> sparse-llvm didn't took this in account which resulted >> in type error in 'add' instructions. >> >> Fix this by catching addition involving pointer and issuing >> a getelementptr' instruction for these. > > I have one related question. In the case of anonymous > structure or union, how to you figure out which series of > GEP it needs to be? I think sparse already lost the element > pointer index information. You can construct it back by looking > at the bit offset. But if there is union then the element point can > have multiple path to reach to the same bit offset. I don't > know how to deal with that. Sparse-llvm appears to bypass the normal struct GEP in LLVM. It basically casts everything to char *, uses GEP to obtain a pointer to member, and then casts it back to member type. So this should work for structs and unions. > >> >> Originally-by: Dibyendu Majumdar <mobile@xxxxxxxxxxxxxxx> >> Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@xxxxxxxxx> >> --- >> sparse-llvm.c | 4 ++++ >> 1 file changed, 4 insertions(+) >> >> diff --git a/sparse-llvm.c b/sparse-llvm.c >> index 27cc1b88c..ee374b217 100644 >> --- a/sparse-llvm.c >> +++ b/sparse-llvm.c >> @@ -472,6 +472,10 @@ static void output_op_binary(struct function *fn, struct instruction *insn) >> case OP_ADD: >> if (symbol_is_fp_type(insn->type)) >> target = LLVMBuildFAdd(fn->builder, lhs, rhs, target_name); >> + else if (LLVMGetTypeKind(LLVMTypeOf(lhs)) == LLVMPointerTypeKind) >> + target = LLVMBuildGEP(fn->builder, lhs, &rhs, 1, ""); >> + else if (LLVMGetTypeKind(LLVMTypeOf(rhs)) == LLVMPointerTypeKind) >> + target = LLVMBuildGEP(fn->builder, rhs, &lhs, 1, ""); > > It seems that you only have one level of indices. Also the OP_ADD use the member > offset of the struct. I am not sure how it map into GEP indices. > Correct me if I am > wrong, it seems to me you use the member offset as element indices. I > think it need > to get a mapping between offset to indices. > This case is more about handing pointer arithmetic correctly. Here GEP is being used as array element access and not for struct member access. Hope this is helpful. Regards Dibyendu -- To unsubscribe from this list: send the line "unsubscribe linux-sparse" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
