Hi!
The r266345 change breaks mingw bootstraps for quite some time.
The problem is that the dynamic realignment is done IMHO way too low.
The biggest problem is that when assign_stack_local_1 decides to do this
dynamic_align_addr, it emits wherever it is currently expanding code about 3
instructions to do something like new_base = (base + (align - 1)) / align *
align
and returns a MEM with that new_base as the XEXP (mem, 0). Unfortunately,
one of the common callers of assign_stack_local_1,
assign_stack_temp_from_type, does temporary stack slot management and reuses
already assigned slots if they are suitable somewhere else. This of course
doesn't work at all if the instructions that set new_base don't dominate one
or more of the other uses.
Another problem is that in way too many cases we decide to choose
BIGGEST_ALIGNMENT for stack slots, even when not strictly needed. E.g. any
BLKmode stack slot requests that BIGGEST_ALIGNMENT, even if TYPE_ALIGN is
much smaller and assign_stack_local_1 even asserts that for BLKmode the
alignment must be BIGGEST_ALIGNMENT. E.g. on mingw with -mavx or -mavx512f
BIGGEST_ALIGNMENT is 256 or 512 bits, but MAX_SUPPORTED_STACK_ALIGNMENT is
128 bits. So the PR84877 change, even if it didn't cause wrong-code, causes
huge amounts of stack slots to be unnecessarily overaligned with dynamic
realignment.
The following patch reverts to the previous behavior and moves this dynamic
stack realignment to the caller that needs it, which doesn't do caching and
where we can do it solely for this overaligned DECL_ALIGN.
If there are other spots that need this, wondering about:
else
copy = assign_temp (type, 1, 0);
in calls.c, either it can be done by using the variable-sized object
case in the then block, or could be done using assign_stack_local +
this short realignment too.
Bootstrapped/regtested on x86_64-linux, i686-linux, powerpc64le-linux,
bootstrapped on powerpc64-linux (regtest still pending there).
Ok for trunk?
2019-01-09 Jakub Jelinek <ja...@redhat.com>
PR middle-end/84877
PR bootstrap/88450
* function.c (assign_stack_local_1): Revert the 2018-11-21 changes.
(assign_parm_setup_block): Do the argument slot realignment here
instead.
--- gcc/function.c.jj 2019-01-09 15:39:26.261153591 +0100
+++ gcc/function.c 2019-01-09 16:17:59.757704567 +0100
@@ -377,7 +377,6 @@ assign_stack_local_1 (machine_mode mode,
poly_int64 bigend_correction = 0;
poly_int64 slot_offset = 0, old_frame_offset;
unsigned int alignment, alignment_in_bits;
- bool dynamic_align_addr = false;
if (align == 0)
{
@@ -396,22 +395,14 @@ assign_stack_local_1 (machine_mode mode,
alignment_in_bits = alignment * BITS_PER_UNIT;
+ /* Ignore alignment if it exceeds MAX_SUPPORTED_STACK_ALIGNMENT. */
if (alignment_in_bits > MAX_SUPPORTED_STACK_ALIGNMENT)
{
- /* If the required alignment exceeds MAX_SUPPORTED_STACK_ALIGNMENT and
- it is not OK to reduce it. Align the slot dynamically. */
- if (mode == BLKmode
- && (kind & ASLK_REDUCE_ALIGN) == 0
- && currently_expanding_to_rtl)
- dynamic_align_addr = true;
- else
- {
- alignment_in_bits = MAX_SUPPORTED_STACK_ALIGNMENT;
- alignment = MAX_SUPPORTED_STACK_ALIGNMENT / BITS_PER_UNIT;
- }
+ alignment_in_bits = MAX_SUPPORTED_STACK_ALIGNMENT;
+ alignment = MAX_SUPPORTED_STACK_ALIGNMENT / BITS_PER_UNIT;
}
- if (SUPPORTS_STACK_ALIGNMENT && !dynamic_align_addr)
+ if (SUPPORTS_STACK_ALIGNMENT)
{
if (crtl->stack_alignment_estimated < alignment_in_bits)
{
@@ -441,42 +432,10 @@ assign_stack_local_1 (machine_mode mode,
}
}
- /* Handle overalignment here for parameter copy on the stack.
- Reserved enough space for it and dynamically align the address.
- No free frame_space is added here. */
- if (dynamic_align_addr)
- {
- rtx allocsize = gen_int_mode (size, Pmode);
- get_dynamic_stack_size (&allocsize, 0, alignment_in_bits, NULL);
-
- /* This is the size of space needed to accommodate required size of data
- with given alignment. */
- poly_int64 len = rtx_to_poly_int64 (allocsize);
- old_frame_offset = frame_offset;
-
- if (FRAME_GROWS_DOWNWARD)
- {
- frame_offset -= len;
- try_fit_stack_local (frame_offset, len, len,
- PREFERRED_STACK_BOUNDARY / BITS_PER_UNIT,
- &slot_offset);
- }
- else
- {
- frame_offset += len;
- try_fit_stack_local (old_frame_offset, len, len,
- PREFERRED_STACK_BOUNDARY / BITS_PER_UNIT,
- &slot_offset);
- }
- goto found_space;
- }
- else
- {
- if (crtl->stack_alignment_needed < alignment_in_bits)
- crtl->stack_alignment_needed = alignment_in_bits;
- if (crtl->max_used_stack_slot_alignment < alignment_in_bits)
- crtl->max_used_stack_slot_alignment = alignment_in_bits;
- }
+ if (crtl->stack_alignment_needed < alignment_in_bits)
+ crtl->stack_alignment_needed = alignment_in_bits;
+ if (crtl->max_used_stack_slot_alignment < alignment_in_bits)
+ crtl->max_used_stack_slot_alignment = alignment_in_bits;
if (mode != BLKmode || maybe_ne (size, 0))
{
@@ -563,12 +522,6 @@ assign_stack_local_1 (machine_mode mode,
(slot_offset + bigend_correction,
Pmode));
- if (dynamic_align_addr)
- {
- addr = align_dynamic_address (addr, alignment_in_bits);
- mark_reg_pointer (addr, alignment_in_bits);
- }
-
x = gen_rtx_MEM (mode, addr);
set_mem_align (x, alignment_in_bits);
MEM_NOTRAP_P (x) = 1;
@@ -2960,8 +2913,21 @@ assign_parm_setup_block (struct assign_p
if (stack_parm == 0)
{
SET_DECL_ALIGN (parm, MAX (DECL_ALIGN (parm), BITS_PER_WORD));
- stack_parm = assign_stack_local (BLKmode, size_stored,
- DECL_ALIGN (parm));
+ if (DECL_ALIGN (parm) > MAX_SUPPORTED_STACK_ALIGNMENT)
+ {
+ rtx allocsize = gen_int_mode (size, Pmode);
+ get_dynamic_stack_size (&allocsize, 0, DECL_ALIGN (parm), NULL);
+ stack_parm = assign_stack_local (BLKmode, UINTVAL (allocsize),
+ MAX_SUPPORTED_STACK_ALIGNMENT);
+ rtx addr = align_dynamic_address (XEXP (stack_parm, 0),
+ DECL_ALIGN (parm));
+ mark_reg_pointer (addr, DECL_ALIGN (parm));
+ stack_parm = gen_rtx_MEM (GET_MODE (stack_parm), addr);
+ MEM_NOTRAP_P (stack_parm) = 1;
+ }
+ else
+ stack_parm = assign_stack_local (BLKmode, size_stored,
+ DECL_ALIGN (parm));
if (known_eq (GET_MODE_SIZE (GET_MODE (entry_parm)), size))
PUT_MODE (stack_parm, GET_MODE (entry_parm));
set_mem_attributes (stack_parm, parm, 1);
Jakub
