Hi Palmer and all,
I have split the patches and triggerred a new thread.
https://www.mail-archive.com/gcc-patches@gcc.gnu.org/msg297206.html
Could you please review at your convenience?
Thanks & BR,
Fei
On 2022-12-01 11:07 Fei Gao <gao...@eswincomputing.com> wrote:
>
>On 2022-12-01 06:50 Palmer Dabbelt <pal...@dabbelt.com> wrote:
>>
>>On Wed, 30 Nov 2022 00:37:17 PST (-0800), gao...@eswincomputing.com wrote:
>>> The stack that save-restore reserves is not well accumulated in stack
>>> allocation and deallocation.
>>> This patch allows less instructions to be used in stack allocation and
>>> deallocation if save-restore enabled,
>>> and also a much clear logic for save-restore stack manipulation.
>>>
>>> before patch:
>>> bar:
>>> call t0,__riscv_save_4
>>> addi sp,sp,-64
>>> ...
>>> li t0,-12288
>>> addi t0,t0,-1968 # optimized out after patch
>>> add sp,sp,t0 # prologue
>>> ...
>>> li t0,12288 # epilogue
>>> addi t0,t0,2000 # optimized out after patch
>>> add sp,sp,t0
>>> ...
>>> addi sp,sp,32
>>> tail __riscv_restore_4
>>>
>>> after patch:
>>> bar:
>>> call t0,__riscv_save_4
>>> addi sp,sp,-2032
>>> ...
>>> li t0,-12288
>>> add sp,sp,t0 # prologue
>>> ...
>>> li t0,12288 # epilogue
>>> add sp,sp,t0
>>> ...
>>> addi sp,sp,2032
>>> tail __riscv_restore_4
>>>
>>> gcc/ChangeLog:
>>>
>>> * config/riscv/riscv.cc (riscv_first_stack_step): add a new
>>>function parameter remaining_size.
>>> (riscv_compute_frame_info): adapt new riscv_first_stack_step
>>>interface.
>>> (riscv_expand_prologue): consider save-restore in stack allocation.
>>> (riscv_expand_epilogue): consider save-restore in stack
>>>deallocation.
>>>
>>> gcc/testsuite/ChangeLog:
>>>
>>> * gcc.target/riscv/stack_save_restore.c: New test.
>>> ---
>>> gcc/config/riscv/riscv.cc | 58 ++++++++++---------
>>> .../gcc.target/riscv/stack_save_restore.c | 40 +++++++++++++
>>> 2 files changed, 70 insertions(+), 28 deletions(-)
>>> create mode 100644 gcc/testsuite/gcc.target/riscv/stack_save_restore.c
>>
>>I guess with the RISC-V backend still being open for things as big as
>>the V port we should probably be taking code like this as well? I
>>wouldn't be opposed to making an exception for the V code and holding
>>everything else back, though.
>>
>>> diff --git a/gcc/config/riscv/riscv.cc b/gcc/config/riscv/riscv.cc
>>> index 05bdba5ab4d..9e92e729a5f 100644
>>> --- a/gcc/config/riscv/riscv.cc
>>> +++ b/gcc/config/riscv/riscv.cc
>>> @@ -4634,7 +4634,7 @@ riscv_save_libcall_count (unsigned mask)
>>> They decrease stack_pointer_rtx but leave frame_pointer_rtx and
>>> hard_frame_pointer_rtx unchanged. */
>>>
>>> -static HOST_WIDE_INT riscv_first_stack_step (struct riscv_frame_info
>>> *frame);
>>> +static HOST_WIDE_INT riscv_first_stack_step (struct riscv_frame_info
>>> *frame, poly_int64 remaining_size);
>>>
>>> /* Handle stack align for poly_int. */
>>> static poly_int64
>>> @@ -4663,7 +4663,7 @@ riscv_compute_frame_info (void)
>>> save/restore t0. We check for this before clearing the frame struct.
>>> */
>>> if (cfun->machine->interrupt_handler_p)
>>> {
>>> - HOST_WIDE_INT step1 = riscv_first_stack_step (frame);
>>> + HOST_WIDE_INT step1 = riscv_first_stack_step (frame,
>>> frame->total_size);
>>> if (! POLY_SMALL_OPERAND_P ((frame->total_size - step1)))
>>> interrupt_save_prologue_temp = true;
>>> }
>>> @@ -4913,31 +4913,31 @@ riscv_restore_reg (rtx reg, rtx mem)
>>> without adding extra instructions. */
>>>
>>> static HOST_WIDE_INT
>>> -riscv_first_stack_step (struct riscv_frame_info *frame)
>>> +riscv_first_stack_step (struct riscv_frame_info *frame, poly_int64
>>> remaining_size)
>>> {
>>> - HOST_WIDE_INT frame_total_constant_size;
>>> - if (!frame->total_size.is_constant ())
>>> - frame_total_constant_size
>>> - = riscv_stack_align (frame->total_size.coeffs[0])
>>> - - riscv_stack_align (frame->total_size.coeffs[1]);
>>> + HOST_WIDE_INT remaining_const_size;
>>> + if (!remaining_size.is_constant ())
>>> + remaining_const_size
>>> + = riscv_stack_align (remaining_size.coeffs[0])
>>> + - riscv_stack_align (remaining_size.coeffs[1]);
>>
>>The alignment looks off here, at least in the email. Worth fixing it up
>>if you're touching the lines anyway.
>
>Sure, i will change RISCV_STACK_ALIGN into riscv_stack_align.
>
>>
>>> else
>>> - frame_total_constant_size = frame->total_size.to_constant ();
>>> + remaining_const_size = remaining_size.to_constant ();
>>>
>>> - if (SMALL_OPERAND (frame_total_constant_size))
>>> - return frame_total_constant_size;
>>> + if (SMALL_OPERAND (remaining_const_size))
>>> + return remaining_const_size;
>>>
>>> HOST_WIDE_INT min_first_step =
>>> - RISCV_STACK_ALIGN ((frame->total_size -
>>> frame->frame_pointer_offset).to_constant());
>>> + RISCV_STACK_ALIGN ((remaining_size -
>>> frame->frame_pointer_offset).to_constant());
>>> HOST_WIDE_INT max_first_step = IMM_REACH / 2 - PREFERRED_STACK_BOUNDARY
>>>/ 8;
>>> - HOST_WIDE_INT min_second_step = frame_total_constant_size -
>>> max_first_step;
>>> + HOST_WIDE_INT min_second_step = remaining_const_size - max_first_step;
>>> gcc_assert (min_first_step <= max_first_step);
>>>
>>> /* As an optimization, use the least-significant bits of the total frame
>>> size, so that the second adjustment step is just LUI + ADD. */
>>> if (!SMALL_OPERAND (min_second_step)
>>> - && frame_total_constant_size % IMM_REACH < IMM_REACH / 2
>>> - && frame_total_constant_size % IMM_REACH >= min_first_step)
>>> - return frame_total_constant_size % IMM_REACH;
>>> + && remaining_const_size % IMM_REACH < IMM_REACH / 2
>>> + && remaining_const_size % IMM_REACH >= min_first_step)
>>> + return remaining_const_size % IMM_REACH;
>>
>>Looks like this entire frame->total_size -> remaining_size conversion
>>could be done as an independent patch that would change no
>>functionality, that's always a nice way to do things as it makes the
>>code easier to read.
>
>Sure, i will split this patch.
>
>>
>>I spent a bit poking around here and nothing wrong is jumping out, but
>>trying to keep all these offset differences in my head is a bit tricky.
>>If you have the time to refactor this to be easier to read that'd be
>>great, otherwise hopefully I (or someone else) will have the time to
>>take a look -- probably not today on my end, though, as I've got some
>>Linux backlog to look at.
>
>I'll try it. Also i propose to add step0 for pre-allocated stack cases like
>save-restore lib call,
>and the future Zcmp in Zc* extension if needed.
>So we have a clear logic of manipulate stack step by step.
>
>>
>>Thanks!
>>
>>> if (TARGET_RVC)
>>> {
>>> @@ -5037,9 +5037,7 @@ riscv_expand_prologue (void)
>>> /* Save the registers. */
>>> if ((frame->mask | frame->fmask) != 0)
>>> {
>>> - HOST_WIDE_INT step1 = riscv_first_stack_step (frame);
>>> - if (size.is_constant ())
>>> - step1 = MIN (size.to_constant(), step1);
>>> + HOST_WIDE_INT step1 = riscv_first_stack_step (frame, size);
>>>
>>> insn = gen_add3_insn (stack_pointer_rtx,
>>> stack_pointer_rtx,
>>> @@ -5142,6 +5140,8 @@ riscv_expand_epilogue (int style)
>>> HOST_WIDE_INT step2 = 0;
>>> bool use_restore_libcall = ((style == NORMAL_RETURN)
>>> && riscv_use_save_libcall (frame));
>>> + unsigned libcall_size = use_restore_libcall ?
>>> + frame->save_libcall_adjustment : 0;
>>> rtx ra = gen_rtx_REG (Pmode, RETURN_ADDR_REGNUM);
>>> rtx insn;
>>>
>>> @@ -5212,13 +5212,18 @@ riscv_expand_epilogue (int style)
>>> REG_NOTES (insn) = dwarf;
>>> }
>>>
>>> + if (use_restore_libcall)
>>> + frame->mask = 0; /* Temporarily fib for GPRs. */
>>> +
>>> /* If we need to restore registers, deallocate as much stack as
>>> possible in the second step without going out of range. */
>>> if ((frame->mask | frame->fmask) != 0)
>>> - {
>>> - step2 = riscv_first_stack_step (frame);
>>> - step1 -= step2;
>>> - }
>>> + step2 = riscv_first_stack_step (frame, frame->total_size -
>>> libcall_size);
>>> +
>>> + if (use_restore_libcall)
>>> + frame->mask = mask; /* Undo the above fib. */
>>> +
>>> + step1 -= step2 + libcall_size;
>>>
>>> /* Set TARGET to BASE + STEP1. */
>>> if (known_gt (step1, 0))
>>> @@ -5272,15 +5277,12 @@ riscv_expand_epilogue (int style)
>>> frame->mask = 0; /* Temporarily fib that we need not save GPRs. */
>>>
>>> /* Restore the registers. */
>>> - riscv_for_each_saved_reg (frame->total_size - step2, riscv_restore_reg,
>>> + riscv_for_each_saved_reg (frame->total_size - step2 - libcall_size,
>>> + riscv_restore_reg,
>>> true, style == EXCEPTION_RETURN);
>>>
>>> if (use_restore_libcall)
>>> - {
>>> frame->mask = mask; /* Undo the above fib. */
>>> - gcc_assert (step2 >= frame->save_libcall_adjustment);
>>> - step2 -= frame->save_libcall_adjustment;
>>> - }
>>>
>>> if (need_barrier_p)
>>> riscv_emit_stack_tie ();
>>> diff --git a/gcc/testsuite/gcc.target/riscv/stack_save_restore.c
>>> b/gcc/testsuite/gcc.target/riscv/stack_save_restore.c
>>> new file mode 100644
>>> index 00000000000..4695ef9469a
>>> --- /dev/null
>>> +++ b/gcc/testsuite/gcc.target/riscv/stack_save_restore.c
>>> @@ -0,0 +1,40 @@
>>> +/* { dg-do compile } */
>>> +/* { dg-options "-march=rv32imafc -mabi=ilp32f -msave-restore -O2
>>> -fno-schedule-insns -fno-schedule-insns2 -fno-unroll-loops -fno-peel-loops"
>>> } */
>>> +/* { dg-final { check-function-bodies "**" "" } } */
>>> +
>>> +char my_getchar();
>>> +float getf();
>>> +
>>> +/*
>>> +**bar:
>>> +** call t0,__riscv_save_4
>>> +** addi sp,sp,-2032
>>> +** ...
>>> +** li t0,-12288
>>> +** add sp,sp,t0
>>> +** ...
>>> +** li t0,12288
>>> +** add sp,sp,t0
>>> +** ...
>>> +** addi sp,sp,2032
>>> +** tail __riscv_restore_4
>>> +*/
>>
>>The test needs to actually check this, it can't just be manual.
>
>I didn't get your point.
>The { dg-final { check-function-bodies "**" "" } } matches the output with the
>expected result above automatically.
>Please let me know your idea.
>
>Thanks & BR,
>Fei
>
>>
>>> +int bar()
>>> +{
>>> + float volatile farray[3568];
>>> +
>>> + float sum = 0;
>>> + float f1 = getf();
>>> + float f2 = getf();
>>> + float f3 = getf();
>>> + float f4 = getf();
>>> +
>>> + for (int i = 0; i < 3568; i++)
>>> + {
>>> + farray[i] = my_getchar() * 1.2;
>>> + sum += farray[i];
>>> + }
>>> +
>>> + return sum + f1 + f2 + f3 + f4;
>>> +}
>>> +
