ping
From: Wilco Dijkstra
Sent: 31 October 2016 18:29
To: GCC Patches
Cc: nd
Subject: [RFC][PATCH][AArch64] Cleanup frame pointer usage
This patch cleans up all code related to the frame pointer. On AArch64 we
emit a frame chain even in cases where the frame pointer is not required.
So make this explicit by introducing a boolean emit_frame_chain in
aarch64_frame record.
When the frame pointer is enabled but not strictly required (eg. no use of
alloca), we emit a frame chain in non-leaf functions, but continue to use the
stack pointer to access locals. This results in smaller code and unwind info.
Also simplify the complex logic in aarch64_override_options_after_change_1
and compute whether the frame chain is required in aarch64_layout_frame
instead. As a result aarch64_frame_pointer_required is now redundant and
aarch64_can_eliminate can be greatly simplified.
Finally convert all callee save/restore functions to use gen_frame_mem.
Bootstrap OK. Any comments?
ChangeLog:
2016-10-31 Wilco Dijkstra <wdijk...@arm.com>
gcc/
* config/aarch64/aarch64.h (aarch64_frame):
Add emit_frame_chain boolean.
* config/aarch64/aarch64.c (aarch64_frame_pointer_required)
Remove.
(aarch64_layout_frame): Initialise emit_frame_chain.
(aarch64_pushwb_single_reg): Use gen_frame_mem.
(aarch64_pop_regs): Likewise.
(aarch64_gen_load_pair): Likewise.
(aarch64_save_callee_saves): Likewise.
(aarch64_restore_callee_saves): Likewise.
(aarch64_expand_prologue): Use emit_frame_chain.
(aarch64_can_eliminate): Simplify. When FP needed or outgoing
arguments are large, eliminate to FP, otherwise SP.
(aarch64_override_options_after_change_1): Simplify.
(TARGET_FRAME_POINTER_REQUIRED): Remove define.
--
diff --git a/gcc/config/aarch64/aarch64.h b/gcc/config/aarch64/aarch64.h
index
fa81e4b853dafcccc08842955288861ec7e7acca..6e32dc9f6f171dde0c182fdd7857230251f71712
100644
--- a/gcc/config/aarch64/aarch64.h
+++ b/gcc/config/aarch64/aarch64.h
@@ -583,6 +583,9 @@ struct GTY (()) aarch64_frame
/* The size of the stack adjustment after saving callee-saves. */
HOST_WIDE_INT final_adjust;
+ /* Store FP,LR and setup a frame pointer. */
+ bool emit_frame_chain;
+
unsigned wb_candidate1;
unsigned wb_candidate2;
diff --git a/gcc/config/aarch64/aarch64.c b/gcc/config/aarch64/aarch64.c
index
f07d771ea343803e054e03f59c8c1efb698bf474..6c06ac18d16f8afa7ee1cc5e8530e285a60e2b0f
100644
--- a/gcc/config/aarch64/aarch64.c
+++ b/gcc/config/aarch64/aarch64.c
@@ -2728,24 +2728,6 @@ aarch64_output_probe_stack_range (rtx reg1, rtx reg2)
return "";
}
-static bool
-aarch64_frame_pointer_required (void)
-{
- /* In aarch64_override_options_after_change
- flag_omit_leaf_frame_pointer turns off the frame pointer by
- default. Turn it back on now if we've not got a leaf
- function. */
- if (flag_omit_leaf_frame_pointer
- && (!crtl->is_leaf || df_regs_ever_live_p (LR_REGNUM)))
- return true;
-
- /* Force a frame pointer for EH returns so the return address is at FP+8. */
- if (crtl->calls_eh_return)
- return true;
-
- return false;
-}
-
/* Mark the registers that need to be saved by the callee and calculate
the size of the callee-saved registers area and frame record (both FP
and LR may be omitted). */
@@ -2758,6 +2740,18 @@ aarch64_layout_frame (void)
if (reload_completed && cfun->machine->frame.laid_out)
return;
+ /* Force a frame chain for EH returns so the return address is at FP+8. */
+ cfun->machine->frame.emit_frame_chain
+ = frame_pointer_needed || crtl->calls_eh_return;
+
+ /* Emit a frame chain if the frame pointer is enabled.
+ If -momit-leaf-frame-pointer is used, do not use a frame chain
+ in leaf functions which do not use LR. */
+ if (flag_omit_frame_pointer == 2
+ && !(flag_omit_leaf_frame_pointer && crtl->is_leaf
+ && !df_regs_ever_live_p (LR_REGNUM)))
+ cfun->machine->frame.emit_frame_chain = true;
+
#define SLOT_NOT_REQUIRED (-2)
#define SLOT_REQUIRED (-1)
@@ -2789,7 +2783,7 @@ aarch64_layout_frame (void)
&& !call_used_regs[regno])
cfun->machine->frame.reg_offset[regno] = SLOT_REQUIRED;
- if (frame_pointer_needed)
+ if (cfun->machine->frame.emit_frame_chain)
{
/* FP and LR are placed in the linkage record. */
cfun->machine->frame.reg_offset[R29_REGNUM] = 0;
@@ -2937,7 +2931,7 @@ aarch64_pushwb_single_reg (machine_mode mode, unsigned
regno,
reg = gen_rtx_REG (mode, regno);
mem = gen_rtx_PRE_MODIFY (Pmode, base_rtx,
plus_constant (Pmode, base_rtx, -adjustment));
- mem = gen_rtx_MEM (mode, mem);
+ mem = gen_frame_mem (mode, mem);
insn = emit_move_insn (mem, reg);
RTX_FRAME_RELATED_P (insn) = 1;
@@ -3011,7 +3005,7 @@ aarch64_pop_regs (unsigned regno1, unsigned regno2,
HOST_WIDE_INT adjustment,
{
rtx mem = plus_constant (Pmode, stack_pointer_rtx, adjustment);
mem = gen_rtx_POST_MODIFY (Pmode, stack_pointer_rtx, mem);
- emit_move_insn (reg1, gen_rtx_MEM (mode, mem));
+ emit_move_insn (reg1, gen_frame_mem (mode, mem));
}
else
{
@@ -3062,8 +3056,6 @@ aarch64_save_callee_saves (machine_mode mode,
HOST_WIDE_INT start_offset,
unsigned start, unsigned limit, bool skip_wb)
{
rtx_insn *insn;
- rtx (*gen_mem_ref) (machine_mode, rtx) = (frame_pointer_needed
- ? gen_frame_mem : gen_rtx_MEM);
unsigned regno;
unsigned regno2;
@@ -3081,8 +3073,8 @@ aarch64_save_callee_saves (machine_mode mode,
HOST_WIDE_INT start_offset,
reg = gen_rtx_REG (mode, regno);
offset = start_offset + cfun->machine->frame.reg_offset[regno];
- mem = gen_mem_ref (mode, plus_constant (Pmode, stack_pointer_rtx,
- offset));
+ mem = gen_frame_mem (mode, plus_constant (Pmode, stack_pointer_rtx,
+ offset));
regno2 = aarch64_next_callee_save (regno + 1, limit);
@@ -3095,8 +3087,8 @@ aarch64_save_callee_saves (machine_mode mode,
HOST_WIDE_INT start_offset,
rtx mem2;
offset = start_offset + cfun->machine->frame.reg_offset[regno2];
- mem2 = gen_mem_ref (mode, plus_constant (Pmode, stack_pointer_rtx,
- offset));
+ mem2 = gen_frame_mem (mode, plus_constant (Pmode, stack_pointer_rtx,
+ offset));
insn = emit_insn (aarch64_gen_store_pair (mode, mem, reg, mem2,
reg2));
@@ -3120,8 +3112,6 @@ aarch64_restore_callee_saves (machine_mode mode,
unsigned limit, bool skip_wb, rtx *cfi_ops)
{
rtx base_rtx = stack_pointer_rtx;
- rtx (*gen_mem_ref) (machine_mode, rtx) = (frame_pointer_needed
- ? gen_frame_mem : gen_rtx_MEM);
unsigned regno;
unsigned regno2;
HOST_WIDE_INT offset;
@@ -3139,7 +3129,7 @@ aarch64_restore_callee_saves (machine_mode mode,
reg = gen_rtx_REG (mode, regno);
offset = start_offset + cfun->machine->frame.reg_offset[regno];
- mem = gen_mem_ref (mode, plus_constant (Pmode, base_rtx, offset));
+ mem = gen_frame_mem (mode, plus_constant (Pmode, base_rtx, offset));
regno2 = aarch64_next_callee_save (regno + 1, limit);
@@ -3151,7 +3141,7 @@ aarch64_restore_callee_saves (machine_mode mode,
rtx mem2;
offset = start_offset + cfun->machine->frame.reg_offset[regno2];
- mem2 = gen_mem_ref (mode, plus_constant (Pmode, base_rtx, offset));
+ mem2 = gen_frame_mem (mode, plus_constant (Pmode, base_rtx, offset));
emit_insn (aarch64_gen_load_pair (mode, reg, mem, reg2, mem2));
*cfi_ops = alloc_reg_note (REG_CFA_RESTORE, reg2, *cfi_ops);
@@ -3217,6 +3207,7 @@ aarch64_expand_prologue (void)
HOST_WIDE_INT callee_offset = cfun->machine->frame.callee_offset;
unsigned reg1 = cfun->machine->frame.wb_candidate1;
unsigned reg2 = cfun->machine->frame.wb_candidate2;
+ bool emit_frame_chain = cfun->machine->frame.emit_frame_chain;
rtx_insn *insn;
if (flag_stack_usage_info)
@@ -3239,7 +3230,7 @@ aarch64_expand_prologue (void)
if (callee_adjust != 0)
aarch64_push_regs (reg1, reg2, callee_adjust);
- if (frame_pointer_needed)
+ if (emit_frame_chain)
{
if (callee_adjust == 0)
aarch64_save_callee_saves (DImode, callee_offset, R29_REGNUM,
@@ -3247,12 +3238,12 @@ aarch64_expand_prologue (void)
insn = emit_insn (gen_add3_insn (hard_frame_pointer_rtx,
stack_pointer_rtx,
GEN_INT (callee_offset)));
- RTX_FRAME_RELATED_P (insn) = 1;
+ RTX_FRAME_RELATED_P (insn) = frame_pointer_needed;
emit_insn (gen_stack_tie (stack_pointer_rtx, hard_frame_pointer_rtx));
}
aarch64_save_callee_saves (DImode, callee_offset, R0_REGNUM, R30_REGNUM,
- callee_adjust != 0 || frame_pointer_needed);
+ callee_adjust != 0 || emit_frame_chain);
aarch64_save_callee_saves (DFmode, callee_offset, V0_REGNUM, V31_REGNUM,
callee_adjust != 0 || frame_pointer_needed);
aarch64_sub_sp (IP1_REGNUM, final_adjust, !frame_pointer_needed);
@@ -5157,36 +5148,13 @@ aarch64_secondary_reload (bool in_p ATTRIBUTE_UNUSED,
rtx x,
}
static bool
-aarch64_can_eliminate (const int from, const int to)
+aarch64_can_eliminate (const int from ATTRIBUTE_UNUSED, const int to)
{
- /* If we need a frame pointer, we must eliminate FRAME_POINTER_REGNUM into
- HARD_FRAME_POINTER_REGNUM and not into STACK_POINTER_REGNUM. */
-
- if (frame_pointer_needed)
- {
- if (from == ARG_POINTER_REGNUM && to == HARD_FRAME_POINTER_REGNUM)
- return true;
- if (from == ARG_POINTER_REGNUM && to == STACK_POINTER_REGNUM)
- return false;
- if (from == FRAME_POINTER_REGNUM && to == STACK_POINTER_REGNUM
- && !cfun->calls_alloca)
- return true;
- if (from == FRAME_POINTER_REGNUM && to == HARD_FRAME_POINTER_REGNUM)
- return true;
-
- return false;
- }
- else
- {
- /* If we decided that we didn't need a leaf frame pointer but then used
- LR in the function, then we'll want a frame pointer after all, so
- prevent this elimination to ensure a frame pointer is used. */
- if (to == STACK_POINTER_REGNUM
- && flag_omit_leaf_frame_pointer
- && df_regs_ever_live_p (LR_REGNUM))
- return false;
- }
-
+ /* If we need a frame pointer, eliminate to HARD_FRAME_POINTER_REGNUM.
+ Use FP as well as with a large number of outgoing arguments so
+ that stack offsets are smaller - this may generate better code. */
+ if (frame_pointer_needed || crtl->outgoing_args_size > 64)
+ return to == HARD_FRAME_POINTER_REGNUM;
return true;
}
@@ -8112,24 +8080,13 @@ aarch64_parse_override_string (const char* input_string,
static void
aarch64_override_options_after_change_1 (struct gcc_options *opts)
{
- /* The logic here is that if we are disabling all frame pointer generation
- then we do not need to disable leaf frame pointer generation as a
- separate operation. But if we are *only* disabling leaf frame pointer
- generation then we set flag_omit_frame_pointer to true, but in
- aarch64_frame_pointer_required we return false only for leaf functions.
-
- PR 70044: We have to be careful about being called multiple times for the
- same function. Once we have decided to set flag_omit_frame_pointer just
- so that we can omit leaf frame pointers, we must then not interpret a
- second call as meaning that all frame pointer generation should be
- omitted. We do this by setting flag_omit_frame_pointer to a special,
- non-zero value. */
- if (opts->x_flag_omit_frame_pointer == 2)
- opts->x_flag_omit_frame_pointer = 0;
-
- if (opts->x_flag_omit_frame_pointer)
- opts->x_flag_omit_leaf_frame_pointer = false;
- else if (opts->x_flag_omit_leaf_frame_pointer)
+ /* PR 70044: We have to be careful about being called multiple times for the
+ same function. This means all changes should be repeatable. */
+
+ /* If the frame pointer is enabled, set the flag to a special value.
+ To implement -momit-leaf-frame-pointer this special value is checked in
+ aarch64_layout_frame. The frame chain is emitted only when required. */
+ if (opts->x_flag_omit_frame_pointer == 0)
opts->x_flag_omit_frame_pointer = 2;
/* If not optimizing for size, set the default
@@ -14126,9 +14083,6 @@ aarch64_optab_supported_p (int op, machine_mode mode1,
machine_mode,
#undef TARGET_FUNCTION_VALUE_REGNO_P
#define TARGET_FUNCTION_VALUE_REGNO_P aarch64_function_value_regno_p
-#undef TARGET_FRAME_POINTER_REQUIRED
-#define TARGET_FRAME_POINTER_REQUIRED aarch64_frame_pointer_required
-
#undef TARGET_GIMPLE_FOLD_BUILTIN
#define TARGET_GIMPLE_FOLD_BUILTIN aarch64_gimple_fold_builtin
