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.
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.
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.
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.
+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;
+}
+
