On 25/08/18 16:43, Luc Van Oostenryck wrote:
> The values produced by expressions are not always used,
> it's normal. However this produce useless code that will
> need to be removed, soon or later.
s/soon/sooner/
>
> Currently, this removal of dead instructions is done as
> part of the normal instruction simplification where each
> kind of instruction are checked if it used or not and
s/if it used/if it is used/
s/and/and,/
ATB,
Ramsay Jones
> if not, the usage is removed from the operands and the
> instruction itself is removed. This has several drawbacks:
> * this is done at each simplification cycle while it is
> only needed just after linearization
> * there is a large overlap between what is needed to correctly
> remove these dead instructions and kill_instruction()
> * instructions which are not simplified are forgotten
> for this and thus never removed.
>
> Change this by adding a separate function to remove these
> deadborn instructions.
>
> Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@xxxxxxxxx>
> ---
> flow.h | 1 +
> simplify.c | 22 ++++++++++++++++++++++
> 2 files changed, 23 insertions(+)
>
> diff --git a/flow.h b/flow.h
> index c8e12cf0f..099767d40 100644
> --- a/flow.h
> +++ b/flow.h
> @@ -20,6 +20,7 @@ extern void simplify_memops(struct entrypoint *ep);
> extern void pack_basic_blocks(struct entrypoint *ep);
>
> extern void convert_instruction_target(struct instruction *insn, pseudo_t src);
> +extern void remove_dead_insns(struct entrypoint *);
> extern int simplify_instruction(struct instruction *);
>
> extern void kill_bb(struct basic_block *);
> diff --git a/simplify.c b/simplify.c
> index a786579e9..066ad04ea 100644
> --- a/simplify.c
> +++ b/simplify.c
> @@ -369,6 +369,28 @@ static int dead_insn(struct instruction *insn, pseudo_t *src1, pseudo_t *src2, p
> return REPEAT_CSE;
> }
>
> +static bool has_target(struct instruction *insn)
> +{
> + return opcode_table[insn->opcode].flags & OPF_TARGET;
> +}
> +
> +void remove_dead_insns(struct entrypoint *ep)
> +{
> + struct basic_block *bb;
> +
> + FOR_EACH_PTR_REVERSE(ep->bbs, bb) {
> + struct instruction *insn;
> + FOR_EACH_PTR_REVERSE(bb->insns, insn) {
> + if (!insn->bb)
> + continue;
> + if (!has_target(insn))
> + continue;
> + if (!has_users(insn->target))
> + kill_instruction(insn);
> + } END_FOR_EACH_PTR_REVERSE(insn);
> + } END_FOR_EACH_PTR_REVERSE(bb);
> +}
> +
> static inline int constant(pseudo_t pseudo)
> {
> return pseudo->type == PSEUDO_VAL;
>
