Re: [PATCH 1/2] CALL_INSN may not be a real function call.

[Hongtao Liu <crazylht@gmail.com>]

Ping,
This is a splitted middle-end patch as a follow up of
https://gcc.gnu.org/pipermail/gcc-patches/2021-June/571544.html

On Thu, Jun 3, 2021 at 2:54 PM liuhongt via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> Use "used" flag for CALL_INSN to indicate it's a fake call. If it's a
> fake call, it won't have its own function stack.
>
> gcc/ChangeLog
>
>         PR target/82735
>         * df-scan.c (df_get_call_refs): When call_insn is a fake call,
>         it won't use stack pointer reg.
>         * final.c (leaf_function_p): When call_insn is a fake call, it
>         won't affect caller as a leaf function.
>         * reg-stack.c (callee_clobbers_any_stack_reg): New.
>         (subst_stack_regs): When call_insn doesn't clobber any stack
>         reg, don't clear the arguments.
>         * rtl.c (shallow_copy_rtx): Don't clear flag used when orig is
>         a insn.
>         * shrink-wrap.c (requires_stack_frame_p): No need for stack
>         frame for a fake call.
>         * rtl.h (FAKE_CALL_P): New macro.
> ---
>  gcc/df-scan.c     |  3 ++-
>  gcc/final.c       |  3 ++-
>  gcc/reg-stack.c   | 18 +++++++++++++++++-
>  gcc/rtl.c         |  6 ++++--
>  gcc/rtl.h         |  5 +++++
>  gcc/shrink-wrap.c |  2 +-
>  6 files changed, 31 insertions(+), 6 deletions(-)
>
> diff --git a/gcc/df-scan.c b/gcc/df-scan.c
> index 6691c3e8357..1268536b3f0 100644
> --- a/gcc/df-scan.c
> +++ b/gcc/df-scan.c
> @@ -3090,7 +3090,8 @@ df_get_call_refs (class df_collection_rec *collection_rec,
>
>    for (i = 0; i < FIRST_PSEUDO_REGISTER; i++)
>      {
> -      if (i == STACK_POINTER_REGNUM)
> +      if (i == STACK_POINTER_REGNUM
> +         && !FAKE_CALL_P (insn_info->insn))
>         /* The stack ptr is used (honorarily) by a CALL insn.  */
>         df_ref_record (DF_REF_BASE, collection_rec, regno_reg_rtx[i],
>                        NULL, bb, insn_info, DF_REF_REG_USE,
> diff --git a/gcc/final.c b/gcc/final.c
> index e0a70fcd830..817f7722cb2 100644
> --- a/gcc/final.c
> +++ b/gcc/final.c
> @@ -4109,7 +4109,8 @@ leaf_function_p (void)
>    for (insn = get_insns (); insn; insn = NEXT_INSN (insn))
>      {
>        if (CALL_P (insn)
> -         && ! SIBLING_CALL_P (insn))
> +         && ! SIBLING_CALL_P (insn)
> +         && ! FAKE_CALL_P (insn))
>         return 0;
>        if (NONJUMP_INSN_P (insn)
>           && GET_CODE (PATTERN (insn)) == SEQUENCE
> diff --git a/gcc/reg-stack.c b/gcc/reg-stack.c
> index 25210f0c17f..1d9ea035cf4 100644
> --- a/gcc/reg-stack.c
> +++ b/gcc/reg-stack.c
> @@ -174,6 +174,7 @@
>  #include "reload.h"
>  #include "tree-pass.h"
>  #include "rtl-iter.h"
> +#include "function-abi.h"
>
>  #ifdef STACK_REGS
>
> @@ -2368,6 +2369,18 @@ subst_asm_stack_regs (rtx_insn *insn, stack_ptr regstack)
>             }
>        }
>  }
> +
> +/* Return true if a function call is allowed to alter some or all bits
> +   of any stack reg.  */
> +static bool
> +callee_clobbers_any_stack_reg (const function_abi & callee_abi)
> +{
> +  for (unsigned regno = FIRST_STACK_REG; regno <= LAST_STACK_REG; regno++)
> +    if (callee_abi.clobbers_at_least_part_of_reg_p (regno))
> +      return true;
> +  return false;
> +}
> +
>
>  /* Substitute stack hard reg numbers for stack virtual registers in
>     INSN.  Non-stack register numbers are not changed.  REGSTACK is the
> @@ -2382,7 +2395,10 @@ subst_stack_regs (rtx_insn *insn, stack_ptr regstack)
>    bool control_flow_insn_deleted = false;
>    int i;
>
> -  if (CALL_P (insn))
> +  /* If the target of the call doesn't clobber any stack registers,
> +     Don't clear the arguments.  */
> +  if (CALL_P (insn)
> +      && callee_clobbers_any_stack_reg (insn_callee_abi (insn)))
>      {
>        int top = regstack->top;
>
> diff --git a/gcc/rtl.c b/gcc/rtl.c
> index b0ba1ff684c..aaee882f5ca 100644
> --- a/gcc/rtl.c
> +++ b/gcc/rtl.c
> @@ -395,8 +395,10 @@ shallow_copy_rtx (const_rtx orig MEM_STAT_DECL)
>      case SCRATCH:
>        break;
>      default:
> -      /* For all other RTXes clear the used flag on the copy.  */
> -      RTX_FLAG (copy, used) = 0;
> +      /* For all other RTXes clear the used flag on the copy.
> +        CALL_INSN use "used" flag to indicate it's a fake call.  */
> +      if (!INSN_P (orig))
> +       RTX_FLAG (copy, used) = 0;
>        break;
>      }
>    return copy;
> diff --git a/gcc/rtl.h b/gcc/rtl.h
> index 35178b5bfac..5ed0d6dd6fa 100644
> --- a/gcc/rtl.h
> +++ b/gcc/rtl.h
> @@ -839,6 +839,11 @@ struct GTY(()) rtvec_def {
>  /* Predicate yielding nonzero iff X is a call insn.  */
>  #define CALL_P(X) (GET_CODE (X) == CALL_INSN)
>
> +/* 1 if RTX is a call_insn for a fake call.
> +   CALL_INSN use "used" flag to indicate it's a fake call.  */
> +#define FAKE_CALL_P(RTX)                                        \
> +  (RTL_FLAG_CHECK1 ("FAKE_CALL_P", (RTX), CALL_INSN)->used)
> +
>  /* Predicate yielding nonzero iff X is an insn that cannot jump.  */
>  #define NONJUMP_INSN_P(X) (GET_CODE (X) == INSN)
>
> diff --git a/gcc/shrink-wrap.c b/gcc/shrink-wrap.c
> index ba7b5cd56fd..5e60f34f749 100644
> --- a/gcc/shrink-wrap.c
> +++ b/gcc/shrink-wrap.c
> @@ -57,7 +57,7 @@ requires_stack_frame_p (rtx_insn *insn, HARD_REG_SET prologue_used,
>    HARD_REG_SET hardregs;
>    unsigned regno;
>
> -  if (CALL_P (insn))
> +  if (CALL_P (insn) && !FAKE_CALL_P (insn))
>      return !SIBLING_CALL_P (insn);
>
>    /* We need a frame to get the unique CFA expected by the unwinder.  */
> --
> 2.18.1
>


-- 
BR,
Hongtao