On 13 March 2017 at 22:54, Dibyendu Majumdar <mobile@xxxxxxxxxxxxxxx> wrote:
> I am investigating a type error in LLVM. Here is the snippet of code:
>
> typedef union GCObject GCObject;
> typedef unsigned char lu_byte;
> typedef double lua_Number;
> typedef union {
> GCObject *gc;
> void *p;
> lua_Number n;
> int b;
> } Value;
> typedef struct lua_TValue {
> Value value;
> int tt;
> } TValue;
> typedef struct UpVal {
> GCObject *next;
> lu_byte tt;
> lu_byte marked;
> TValue *v;
> union {
> TValue value;
> struct {
> struct UpVal *prev;
> struct UpVal *next;
> } l;
> } u;
> } UpVal;
> static void close(UpVal *uv)
> {
> uv->v = &uv->u.value;
> }
>
> The linearized output is:
>
> close:
> .L0:
> <entry-point>
> add.64 %r2 <- %arg1, $24
> store.64 %r2 -> 16[%arg1]
> ret
>
> The result of the add operation ends up the same type as arg1 which is
> UpVal*. But this is then assigned to uv->v which is expected to be
> TValue*. So LLVM doesn't like it.
>
> While in this case we could cast to the expected value before the
> store - I am worried that in other cases where the value is read and
> used somewhere it will have the wrong type.
>
> I see that the add instruction's type is 'void *'.
>
> Any suggestions on how to solve this issue?
>
For now I am casting the stored value in output_op_store():
target_in = pseudo_to_value(C, fn, insn, insn->target);
desttype = insn_symbol_type(C, fn->module, insn);
/* Cast to the right type - to resolve issue with union types */
target_in = LLVMBuildBitCast(fn->builder, target_in, desttype, "");
/* perform store */
LLVMBuildStore(fn->builder, target_in, addr);
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