[v3] x86: Properly find the maximum stack slot alignment

Don't assume that stack slots can only be accessed by stack or frame
registers.  We first find all registers defined by stack or frame
registers.  Then check memory accesses by such registers, including
stack and frame registers.

gcc/

	PR target/109780
	* config/i386/i386.cc (ix86_update_stack_alignment): New.
	(ix86_find_all_reg_use): Likewise.
	(ix86_find_max_used_stack_alignment): Also check memory accesses
	from registers defined by stack or frame registers.

gcc/testsuite/

	PR target/109780
	* g++.target/i386/pr109780-1.C: New test.
	* gcc.target/i386/pr109780-1.c: Likewise.
	* gcc.target/i386/pr109780-2.c: Likewise.
---
 gcc/config/i386/i386.cc                    | 128 +++++++++++++++++----
 gcc/testsuite/g++.target/i386/pr109780-1.C |  72 ++++++++++++
 gcc/testsuite/gcc.target/i386/pr109780-1.c |  14 +++
 gcc/testsuite/gcc.target/i386/pr109780-2.c |  21 ++++
 4 files changed, 214 insertions(+), 21 deletions(-)
 create mode 100644 gcc/testsuite/g++.target/i386/pr109780-1.C
 create mode 100644 gcc/testsuite/gcc.target/i386/pr109780-1.c
 create mode 100644 gcc/testsuite/gcc.target/i386/pr109780-2.c

On Mon, Jul 24, 2023 at 10:36 PM H.J. Lu via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> Don't assume that stack slots can only be accessed by stack or frame
> registers.  We first find all registers defined by stack or frame
> registers.  Then check memory accesses by such registers, including
> stack and frame registers.

Looks good to me from an algorithmic/DF perspective - I'm leaving it for
x86 maintainers to assess the functional bits.

Thanks,
Richard.

> gcc/
>
>         PR target/109780
>         * config/i386/i386.cc (ix86_update_stack_alignment): New.
>         (ix86_find_all_reg_use): Likewise.
>         (ix86_find_max_used_stack_alignment): Also check memory accesses
>         from registers defined by stack or frame registers.
>
> gcc/testsuite/
>
>         PR target/109780
>         * g++.target/i386/pr109780-1.C: New test.
>         * gcc.target/i386/pr109780-1.c: Likewise.
>         * gcc.target/i386/pr109780-2.c: Likewise.
> ---
>  gcc/config/i386/i386.cc                    | 128 +++++++++++++++++----
>  gcc/testsuite/g++.target/i386/pr109780-1.C |  72 ++++++++++++
>  gcc/testsuite/gcc.target/i386/pr109780-1.c |  14 +++
>  gcc/testsuite/gcc.target/i386/pr109780-2.c |  21 ++++
>  4 files changed, 214 insertions(+), 21 deletions(-)
>  create mode 100644 gcc/testsuite/g++.target/i386/pr109780-1.C
>  create mode 100644 gcc/testsuite/gcc.target/i386/pr109780-1.c
>  create mode 100644 gcc/testsuite/gcc.target/i386/pr109780-2.c
>
> diff --git a/gcc/config/i386/i386.cc b/gcc/config/i386/i386.cc
> index caca74d6dec..b71fd9401ef 100644
> --- a/gcc/config/i386/i386.cc
> +++ b/gcc/config/i386/i386.cc
> @@ -8084,6 +8084,65 @@ output_probe_stack_range (rtx reg, rtx end)
>    return "";
>  }
>
> +/* Update the maximum stack slot alignment from memory alignment in
> +   PAT.  */
> +
> +static void
> +ix86_update_stack_alignment (rtx, const_rtx pat, void *data)
> +{
> +  /* This insn may reference stack slot.  Update the maximum stack slot
> +     alignment.  */
> +  subrtx_iterator::array_type array;
> +  FOR_EACH_SUBRTX (iter, array, pat, ALL)
> +    if (MEM_P (*iter))
> +      {
> +       unsigned int alignment = MEM_ALIGN (*iter);
> +       unsigned int *stack_alignment
> +         = (unsigned int *) data;
> +       if (alignment > *stack_alignment)
> +         *stack_alignment = alignment;
> +       break;
> +      }
> +}
> +
> +/* Find all registers defined with REG.  */
> +
> +static void
> +ix86_find_all_reg_use (HARD_REG_SET &stack_slot_access,
> +                      unsigned int reg, auto_bitmap &worklist)
> +{
> +  for (df_ref ref = DF_REG_USE_CHAIN (reg);
> +       ref != NULL;
> +       ref = DF_REF_NEXT_REG (ref))
> +    {
> +      if (DF_REF_IS_ARTIFICIAL (ref))
> +       continue;
> +
> +      rtx_insn *insn = DF_REF_INSN (ref);
> +      if (!NONDEBUG_INSN_P (insn))
> +       continue;
> +
> +      rtx set = single_set (insn);
> +      if (!set)
> +       continue;
> +
> +      rtx src = SET_SRC (set);
> +      if (MEM_P (src))
> +       continue;
> +
> +      rtx dest = SET_DEST (set);
> +      if (!REG_P (dest))
> +       continue;
> +
> +      if (TEST_HARD_REG_BIT (stack_slot_access, REGNO (dest)))
> +       continue;
> +
> +      /* Add this register to stack_slot_access.  */
> +      add_to_hard_reg_set (&stack_slot_access, Pmode, REGNO (dest));
> +      bitmap_set_bit (worklist, REGNO (dest));
> +    }
> +}
> +
>  /* Set stack_frame_required to false if stack frame isn't required.
>     Update STACK_ALIGNMENT to the largest alignment, in bits, of stack
>     slot used if stack frame is required and CHECK_STACK_SLOT is true.  */
> @@ -8102,10 +8161,6 @@ ix86_find_max_used_stack_alignment (unsigned int &stack_alignment,
>    add_to_hard_reg_set (&set_up_by_prologue, Pmode,
>                        HARD_FRAME_POINTER_REGNUM);
>
> -  /* The preferred stack alignment is the minimum stack alignment.  */
> -  if (stack_alignment > crtl->preferred_stack_boundary)
> -    stack_alignment = crtl->preferred_stack_boundary;
> -
>    bool require_stack_frame = false;
>
>    FOR_EACH_BB_FN (bb, cfun)
> @@ -8117,27 +8172,58 @@ ix86_find_max_used_stack_alignment (unsigned int &stack_alignment,
>                                        set_up_by_prologue))
>           {
>             require_stack_frame = true;
> -
> -           if (check_stack_slot)
> -             {
> -               /* Find the maximum stack alignment.  */
> -               subrtx_iterator::array_type array;
> -               FOR_EACH_SUBRTX (iter, array, PATTERN (insn), ALL)
> -                 if (MEM_P (*iter)
> -                     && (reg_mentioned_p (stack_pointer_rtx,
> -                                          *iter)
> -                         || reg_mentioned_p (frame_pointer_rtx,
> -                                             *iter)))
> -                   {
> -                     unsigned int alignment = MEM_ALIGN (*iter);
> -                     if (alignment > stack_alignment)
> -                       stack_alignment = alignment;
> -                   }
> -             }
> +           break;
>           }
>      }
>
>    cfun->machine->stack_frame_required = require_stack_frame;
> +
> +  /* Stop if we don't need to check stack slot.  */
> +  if (!check_stack_slot)
> +    return;
> +
> +  /* The preferred stack alignment is the minimum stack alignment.  */
> +  if (stack_alignment > crtl->preferred_stack_boundary)
> +    stack_alignment = crtl->preferred_stack_boundary;
> +
> +  HARD_REG_SET stack_slot_access;
> +  CLEAR_HARD_REG_SET (stack_slot_access);
> +
> +  /* Stack slot can be accessed by stack pointer, frame pointer or
> +     registers defined by stack pointer or frame pointer.  */
> +  auto_bitmap worklist;
> +  add_to_hard_reg_set (&stack_slot_access, Pmode,
> +                      STACK_POINTER_REGNUM);
> +  bitmap_set_bit (worklist, STACK_POINTER_REGNUM);
> +  if (frame_pointer_needed)
> +    {
> +      add_to_hard_reg_set (&stack_slot_access, Pmode,
> +                          HARD_FRAME_POINTER_REGNUM);
> +      bitmap_set_bit (worklist, HARD_FRAME_POINTER_REGNUM);
> +    }
> +  unsigned int reg;
> +  do
> +    {
> +      reg = bitmap_clear_first_set_bit (worklist);
> +      ix86_find_all_reg_use (stack_slot_access, reg, worklist);
> +    }
> +  while (!bitmap_empty_p (worklist));
> +
> +  hard_reg_set_iterator hrsi;
> +  EXECUTE_IF_SET_IN_HARD_REG_SET (stack_slot_access, 0, reg, hrsi)
> +    for (df_ref ref = DF_REG_USE_CHAIN (reg);
> +        ref != NULL;
> +        ref = DF_REF_NEXT_REG (ref))
> +      {
> +       if (DF_REF_IS_ARTIFICIAL (ref))
> +         continue;
> +
> +       rtx_insn *insn = DF_REF_INSN (ref);
> +       if (!NONDEBUG_INSN_P (insn))
> +         continue;
> +       note_stores (insn, ix86_update_stack_alignment,
> +                    &stack_alignment);
> +      }
>  }
>
>  /* Finalize stack_realign_needed and frame_pointer_needed flags, which
> diff --git a/gcc/testsuite/g++.target/i386/pr109780-1.C b/gcc/testsuite/g++.target/i386/pr109780-1.C
> new file mode 100644
> index 00000000000..7e3eabdec94
> --- /dev/null
> +++ b/gcc/testsuite/g++.target/i386/pr109780-1.C
> @@ -0,0 +1,72 @@
> +/* { dg-do compile } */
> +/* { dg-require-effective-target c++17 } */
> +/* { dg-options "-O2 -mavx2 -mtune=haswell" } */
> +
> +template <typename _Tp> struct remove_reference {
> +  using type = __remove_reference(_Tp);
> +};
> +template <typename T> struct MaybeStorageBase {
> +  T val;
> +  struct Union {
> +    ~Union();
> +  } mStorage;
> +};
> +template <typename T> struct MaybeStorage : MaybeStorageBase<T> {
> +  char mIsSome;
> +};
> +template <typename T, typename U = typename remove_reference<T>::type>
> +constexpr MaybeStorage<U> Some(T &&);
> +template <typename T, typename U> constexpr MaybeStorage<U> Some(T &&aValue) {
> +  return {aValue};
> +}
> +template <class> struct Span {
> +  int operator[](long idx) {
> +    int *__trans_tmp_4;
> +    if (__builtin_expect(idx, 0))
> +      *(int *)__null = false;
> +    __trans_tmp_4 = storage_.data();
> +    return __trans_tmp_4[idx];
> +  }
> +  struct {
> +    int *data() { return data_; }
> +    int *data_;
> +  } storage_;
> +};
> +struct Variant {
> +  template <typename RefT> Variant(RefT) {}
> +};
> +long from_i, from___trans_tmp_9;
> +namespace js::intl {
> +struct DecimalNumber {
> +  Variant string_;
> +  unsigned long significandStart_;
> +  unsigned long significandEnd_;
> +  bool zero_ = false;
> +  bool negative_;
> +  template <typename CharT> DecimalNumber(CharT string) : string_(string) {}
> +  template <typename CharT>
> +  static MaybeStorage<DecimalNumber> from(Span<const CharT>);
> +  void from();
> +};
> +} // namespace js::intl
> +void js::intl::DecimalNumber::from() {
> +  Span<const char16_t> __trans_tmp_3;
> +  from(__trans_tmp_3);
> +}
> +template <typename CharT>
> +MaybeStorage<js::intl::DecimalNumber>
> +js::intl::DecimalNumber::from(Span<const CharT> chars) {
> +  DecimalNumber number(chars);
> +  if (auto ch = chars[from_i]) {
> +    from_i++;
> +    number.negative_ = ch == '-';
> +  }
> +  while (from___trans_tmp_9 && chars[from_i])
> +    ;
> +  if (chars[from_i])
> +    while (chars[from_i - 1])
> +      number.zero_ = true;
> +  return Some(number);
> +}
> +
> +/* { dg-final { scan-assembler-not "and\[lq\]?\[^\\n\]*-32,\[^\\n\]*sp" } } */
> diff --git a/gcc/testsuite/gcc.target/i386/pr109780-1.c b/gcc/testsuite/gcc.target/i386/pr109780-1.c
> new file mode 100644
> index 00000000000..6b06947f2a5
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/i386/pr109780-1.c
> @@ -0,0 +1,14 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O3 -march=skylake" } */
> +
> +char perm[64];
> +
> +void
> +__attribute__((noipa))
> +foo (int n)
> +{
> +  for (int i = 0; i < n; ++i)
> +    perm[i] = i;
> +}
> +
> +/* { dg-final { scan-assembler-not "and\[lq\]?\[^\\n\]*-32,\[^\\n\]*sp" } } */
> diff --git a/gcc/testsuite/gcc.target/i386/pr109780-2.c b/gcc/testsuite/gcc.target/i386/pr109780-2.c
> new file mode 100644
> index 00000000000..152da06c6ad
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/i386/pr109780-2.c
> @@ -0,0 +1,21 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O3 -march=skylake" } */
> +
> +#define N 9
> +
> +void
> +f (double x, double y, double *res)
> +{
> +  y = -y;
> +  for (int i = 0; i < N; ++i)
> +    {
> +      double tmp = y;
> +      y = x;
> +      x = tmp;
> +      res[i] = i;
> +    }
> +  res[N] = y * y;
> +  res[N + 1] = x;
> +}
> +
> +/* { dg-final { scan-assembler-not "and\[lq\]?\[^\\n\]*-32,\[^\\n\]*sp" } } */
> --
> 2.41.0
>