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;
>> +}
>> +
