In the example below, 'x' is once placed on the stack frame and then read
into registers as the argument value of bar():
/* example */
struct foo {
int a, b;
};
extern struct foo bar(struct foo);
struct foo test(void) {
struct foo x = { 0, 1 };
return bar(x);
}
Thanks to the dead store elimination, the initialization of 'x' turns into
merely loading the immediates to registers, but corresponding stack frame
growth is not rolled back. As a result:
;; prereq: the CALL0 ABI
;; before
test:
addi sp, sp, -16 // unused stack frame allocation/freeing
movi.n a2, 0
movi.n a3, 1
addi sp, sp, 16 // because no instructions that refer to
j.l bar, a9 // the stack pointer between the two
This patch eliminates such unused stack frame allocation/freeing:
;; after
test:
movi.n a2, 0
movi.n a3, 1
j.l bar, a9
gcc/ChangeLog:
* config/xtensa/xtensa.cc (machine_function): New member to track
the insns for stack pointer adjustment inside of the pro/epilogue.
(xtensa_emit_adjust_stack_pointer): New function to share the
common codes and to record the insns for stack pointer adjustment.
(xtensa_expand_prologue): Change to use the function mentioned
above when using the CALL0 ABI.
(xtensa_expand_prologue): Ditto.
And also change to cancel emitting the insns for the stack pointer
adjustment if only used for its own.
---
gcc/config/xtensa/xtensa.cc | 221 ++++++++++++++++++------------------
1 file changed, 110 insertions(+), 111 deletions(-)
diff --git a/gcc/config/xtensa/xtensa.cc b/gcc/config/xtensa/xtensa.cc
index b673b6764da..cd509876fd2 100644
--- a/gcc/config/xtensa/xtensa.cc
+++ b/gcc/config/xtensa/xtensa.cc
@@ -102,6 +102,7 @@ struct GTY(()) machine_function
int callee_save_size;
bool frame_laid_out;
bool epilogue_done;
+ hash_set<rtx_insn *> *logues_a1_adjusts;
};
/* Vector, indexed by hard register number, which contains 1 for a
@@ -3048,7 +3049,7 @@ xtensa_output_literal (FILE *file, rtx x, machine_mode
mode, int labelno)
}
static bool
-xtensa_call_save_reg(int regno)
+xtensa_call_save_reg (int regno)
{
if (TARGET_WINDOWED_ABI)
return false;
@@ -3084,7 +3085,7 @@ compute_frame_size (poly_int64 size)
cfun->machine->callee_save_size = 0;
for (regno = 0; regno < FIRST_PSEUDO_REGISTER; ++regno)
{
- if (xtensa_call_save_reg(regno))
+ if (xtensa_call_save_reg (regno))
cfun->machine->callee_save_size += UNITS_PER_WORD;
}
@@ -3143,6 +3144,49 @@ xtensa_initial_elimination_offset (int from, int to
ATTRIBUTE_UNUSED)
and the total number of words must be a multiple of 128 bits. */
#define MIN_FRAME_SIZE (8 * UNITS_PER_WORD)
+static rtx_insn *
+xtensa_emit_adjust_stack_pointer (HOST_WIDE_INT offset, bool need_note)
+{
+ rtx_insn *insn;
+
+ if (xtensa_simm8 (offset)
+ || xtensa_simm8x256 (offset))
+ insn = emit_insn (gen_addsi3 (stack_pointer_rtx, stack_pointer_rtx,
+ GEN_INT (offset)));
+ else
+ {
+ rtx tmp_reg = gen_rtx_REG (Pmode, A9_REG);
+ rtx_insn* tmp_insn;
+
+ if (offset < 0)
+ {
+ tmp_insn = emit_move_insn (tmp_reg, GEN_INT (-offset));
+ insn = emit_insn (gen_subsi3 (stack_pointer_rtx, stack_pointer_rtx,
+ tmp_reg));
+ }
+ else
+ {
+ tmp_insn = emit_move_insn (tmp_reg, GEN_INT (offset));
+ insn = emit_insn (gen_addsi3 (stack_pointer_rtx, stack_pointer_rtx,
+ tmp_reg));
+ }
+ cfun->machine->logues_a1_adjusts->add (tmp_insn);
+ }
+
+ if (need_note)
+ {
+ rtx note_rtx = gen_rtx_SET (stack_pointer_rtx,
+ plus_constant (Pmode, stack_pointer_rtx,
+ offset));
+
+ RTX_FRAME_RELATED_P (insn) = 1;
+ add_reg_note (insn, REG_FRAME_RELATED_EXPR, note_rtx);
+ }
+
+ cfun->machine->logues_a1_adjusts->add (insn);
+ return insn;
+}
+
void
xtensa_expand_prologue (void)
{
@@ -3175,16 +3219,12 @@ xtensa_expand_prologue (void)
HOST_WIDE_INT offset = 0;
int callee_save_size = cfun->machine->callee_save_size;
+ cfun->machine->logues_a1_adjusts = new hash_set<rtx_insn *>;
+
/* -128 is a limit of single addi instruction. */
if (IN_RANGE (total_size, 1, 128))
{
- insn = emit_insn (gen_addsi3 (stack_pointer_rtx, stack_pointer_rtx,
- GEN_INT (-total_size)));
- RTX_FRAME_RELATED_P (insn) = 1;
- note_rtx = gen_rtx_SET (stack_pointer_rtx,
- plus_constant (Pmode, stack_pointer_rtx,
- -total_size));
- add_reg_note (insn, REG_FRAME_RELATED_EXPR, note_rtx);
+ insn = xtensa_emit_adjust_stack_pointer (-total_size, true);
offset = total_size - UNITS_PER_WORD;
}
else if (callee_save_size)
@@ -3194,75 +3234,34 @@ xtensa_expand_prologue (void)
* move it to its final location. */
if (total_size > 1024)
{
- insn = emit_insn (gen_addsi3 (stack_pointer_rtx,
stack_pointer_rtx,
- GEN_INT (-callee_save_size)));
- RTX_FRAME_RELATED_P (insn) = 1;
- note_rtx = gen_rtx_SET (stack_pointer_rtx,
- plus_constant (Pmode, stack_pointer_rtx,
- -callee_save_size));
- add_reg_note (insn, REG_FRAME_RELATED_EXPR, note_rtx);
+ insn = xtensa_emit_adjust_stack_pointer (-callee_save_size,
+ true);
offset = callee_save_size - UNITS_PER_WORD;
}
else
{
- if (xtensa_simm8x256 (-total_size))
- insn = emit_insn (gen_addsi3 (stack_pointer_rtx,
- stack_pointer_rtx,
- GEN_INT (-total_size)));
- else
- {
- rtx tmp_reg = gen_rtx_REG (Pmode, A9_REG);
- emit_move_insn (tmp_reg, GEN_INT (total_size));
- insn = emit_insn (gen_subsi3 (stack_pointer_rtx,
- stack_pointer_rtx, tmp_reg));
- }
- RTX_FRAME_RELATED_P (insn) = 1;
- note_rtx = gen_rtx_SET (stack_pointer_rtx,
- plus_constant (Pmode, stack_pointer_rtx,
- -total_size));
- add_reg_note (insn, REG_FRAME_RELATED_EXPR, note_rtx);
+ insn = xtensa_emit_adjust_stack_pointer (-total_size, true);
offset = total_size - UNITS_PER_WORD;
}
}
for (regno = 0; regno < FIRST_PSEUDO_REGISTER; ++regno)
- {
- if (xtensa_call_save_reg(regno))
- {
- rtx x = gen_rtx_PLUS (Pmode, stack_pointer_rtx, GEN_INT (offset));
- rtx mem = gen_frame_mem (SImode, x);
- rtx reg = gen_rtx_REG (SImode, regno);
-
- offset -= UNITS_PER_WORD;
- insn = emit_move_insn (mem, reg);
- RTX_FRAME_RELATED_P (insn) = 1;
- add_reg_note (insn, REG_FRAME_RELATED_EXPR,
- gen_rtx_SET (mem, reg));
- }
- }
+ if (xtensa_call_save_reg (regno))
+ {
+ rtx x = gen_rtx_PLUS (Pmode, stack_pointer_rtx, GEN_INT (offset));
+ rtx mem = gen_frame_mem (SImode, x);
+ rtx reg = gen_rtx_REG (SImode, regno);
+
+ offset -= UNITS_PER_WORD;
+ insn = emit_move_insn (mem, reg);
+ RTX_FRAME_RELATED_P (insn) = 1;
+ add_reg_note (insn, REG_FRAME_RELATED_EXPR,
+ gen_rtx_SET (mem, reg));
+ }
if (total_size > 1024
|| (!callee_save_size && total_size > 128))
- {
- if (xtensa_simm8x256 (callee_save_size - total_size))
- insn = emit_insn (gen_addsi3 (stack_pointer_rtx,
- stack_pointer_rtx,
- GEN_INT (callee_save_size -
- total_size)));
- else
- {
- rtx tmp_reg = gen_rtx_REG (Pmode, A9_REG);
- emit_move_insn (tmp_reg, GEN_INT (total_size -
- callee_save_size));
- insn = emit_insn (gen_subsi3 (stack_pointer_rtx,
- stack_pointer_rtx, tmp_reg));
- }
- RTX_FRAME_RELATED_P (insn) = 1;
- note_rtx = gen_rtx_SET (stack_pointer_rtx,
- plus_constant (Pmode, stack_pointer_rtx,
- callee_save_size -
- total_size));
- add_reg_note (insn, REG_FRAME_RELATED_EXPR, note_rtx);
- }
+ insn = xtensa_emit_adjust_stack_pointer (callee_save_size - total_size,
+ true);
}
if (frame_pointer_needed)
@@ -3326,24 +3325,14 @@ xtensa_expand_epilogue (bool sibcall_p)
{
int regno;
HOST_WIDE_INT offset;
+ df_ref ref;
+ bool stack_pointer_used = false;
if (cfun->machine->current_frame_size > (frame_pointer_needed ? 127 :
1024))
{
- if (xtensa_simm8x256 (cfun->machine->current_frame_size -
- cfun->machine->callee_save_size))
- emit_insn (gen_addsi3 (stack_pointer_rtx, frame_pointer_needed ?
- hard_frame_pointer_rtx : stack_pointer_rtx,
- GEN_INT (cfun->machine->current_frame_size -
- cfun->machine->callee_save_size)));
- else
- {
- rtx tmp_reg = gen_rtx_REG (Pmode, A9_REG);
- emit_move_insn (tmp_reg, GEN_INT
(cfun->machine->current_frame_size -
-
cfun->machine->callee_save_size));
- emit_insn (gen_addsi3 (stack_pointer_rtx, frame_pointer_needed ?
- hard_frame_pointer_rtx : stack_pointer_rtx,
- tmp_reg));
- }
+ xtensa_emit_adjust_stack_pointer (cfun->machine->current_frame_size -
+ cfun->machine->callee_save_size,
+ false);
offset = cfun->machine->callee_save_size - UNITS_PER_WORD;
}
else
@@ -3359,19 +3348,18 @@ xtensa_expand_epilogue (bool sibcall_p)
emit_insn (gen_blockage ());
for (regno = 0; regno < FIRST_PSEUDO_REGISTER; ++regno)
- {
- if (xtensa_call_save_reg(regno))
- {
- rtx x = gen_rtx_PLUS (Pmode, stack_pointer_rtx, GEN_INT (offset));
- rtx reg;
-
- offset -= UNITS_PER_WORD;
- emit_move_insn (reg = gen_rtx_REG (SImode, regno),
- gen_frame_mem (SImode, x));
- if (regno == A0_REG && sibcall_p)
- emit_use (reg);
- }
- }
+ if (xtensa_call_save_reg (regno))
+ {
+ rtx x = gen_rtx_PLUS (Pmode, stack_pointer_rtx, GEN_INT (offset));
+ rtx reg;
+
+ offset -= UNITS_PER_WORD;
+ emit_move_insn (reg = gen_rtx_REG (SImode, regno),
+ gen_frame_mem (SImode, x));
+ if (regno == A0_REG && sibcall_p)
+ emit_use (reg);
+ stack_pointer_used = true;
+ }
if (cfun->machine->current_frame_size > 0)
{
@@ -3384,31 +3372,42 @@ xtensa_expand_epilogue (bool sibcall_p)
else
offset = cfun->machine->callee_save_size;
if (offset)
- emit_insn (gen_addsi3 (stack_pointer_rtx,
- stack_pointer_rtx,
- GEN_INT (offset)));
+ xtensa_emit_adjust_stack_pointer (offset, false);
}
else
- {
- if (xtensa_simm8x256 (cfun->machine->current_frame_size))
- emit_insn (gen_addsi3 (stack_pointer_rtx, stack_pointer_rtx,
- GEN_INT
(cfun->machine->current_frame_size)));
- else
- {
- rtx tmp_reg = gen_rtx_REG (Pmode, A9_REG);
- emit_move_insn (tmp_reg,
- GEN_INT (cfun->machine->current_frame_size));
- emit_insn (gen_addsi3 (stack_pointer_rtx, stack_pointer_rtx,
- tmp_reg));
- }
- }
+ xtensa_emit_adjust_stack_pointer (cfun->machine->current_frame_size,
+ false);
}
if (crtl->calls_eh_return)
emit_insn (gen_add3_insn (stack_pointer_rtx,
stack_pointer_rtx,
EH_RETURN_STACKADJ_RTX));
+
+ /* Check if the function body uses the stack pointer. */
+ for (ref = DF_REG_USE_CHAIN (A1_REG);
+ ref; ref = DF_REF_NEXT_REG (ref))
+ if (DF_REF_CLASS (ref) == DF_REF_REGULAR)
+ {
+ stack_pointer_used = true;
+ break;
+ }
+
+ /* Undo the insns if the stack pointer is only used for its own
+ adjustment. */
+ if (! (stack_pointer_used
+ || frame_pointer_needed
+ || crtl->calls_eh_return))
+ for (const auto &insn : *cfun->machine->logues_a1_adjusts)
+ {
+ rtx note = find_reg_note (insn, REG_FRAME_RELATED_EXPR, NULL);
+
+ if (note)
+ remove_note (insn, note);
+ PATTERN (insn) = const0_rtx;
+ }
}
+
cfun->machine->epilogue_done = true;
if (!sibcall_p)
emit_jump_insn (gen_return ());
--
2.20.1
