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| author | Wilco Dijkstra <wdijkstr@arm.com> | 2017-09-05 13:27:58 +0000 |
|---|---|---|
| committer | Wilco Dijkstra <wilco@gcc.gnu.org> | 2017-09-05 13:27:58 +0000 |
| commit | ae85ad3a95d6df3c4131d02fd327809a29d10b33 (patch) | |
| tree | 7280c7e1c75597c2c29f62ff781b46e1369249c9 /gcc/explow.c | |
| parent | 54c430044ba9a35a590e591108b184535eba5763 (diff) | |
| download | gcc-ae85ad3a95d6df3c4131d02fd327809a29d10b33.tar.gz | |
Improve alloca alignment
This patch improves alloca alignment. Currently alloca reserves
too much space as it aligns twice, and generates unnecessary stack
alignment code.
When the requested alignment is lower than the stack alignment, no
extra alignment is needed. If the requested alignment is higher,
we need to increase the size by the difference of the requested
alignment and the stack alignment. As a result, the alloca alignment
is exactly as expected:
alloca (16):
sub sp, sp, #16
mov x1, sp
alloca (x):
add x0, x0, 15
and x0, x0, -16
sub sp, sp, x0
mov x0, sp
__builtin_alloca_with_align (x, 512):
add x0, x0, 63
and x0, x0, -16
sub sp, sp, x0
add x0, sp, 63
and x0, x0, -64
gcc/
* explow.c (get_dynamic_stack_size): Improve dynamic alignment.
From-SVN: r251713
Diffstat (limited to 'gcc/explow.c')
| -rw-r--r-- | gcc/explow.c | 21 |
1 files changed, 13 insertions, 8 deletions
diff --git a/gcc/explow.c b/gcc/explow.c index 13736a586d8..638dc5f8f0f 100644 --- a/gcc/explow.c +++ b/gcc/explow.c @@ -1240,15 +1240,20 @@ get_dynamic_stack_size (rtx *psize, unsigned size_align, example), so we must preventively align the value. We leave space in SIZE for the hole that might result from the alignment operation. */ - extra = (required_align - BITS_PER_UNIT) / BITS_PER_UNIT; - size = plus_constant (Pmode, size, extra); - size = force_operand (size, NULL_RTX); - - if (flag_stack_usage_info && pstack_usage_size) - *pstack_usage_size += extra; + /* Since the stack is presumed to be aligned before this allocation, + we only need to increase the size of the allocation if the required + alignment is more than the stack alignment. */ + if (required_align > STACK_BOUNDARY) + { + extra = (required_align - STACK_BOUNDARY) / BITS_PER_UNIT; + size = plus_constant (Pmode, size, extra); + size = force_operand (size, NULL_RTX); + if (size_align > STACK_BOUNDARY) + size_align = STACK_BOUNDARY; - if (extra && size_align > BITS_PER_UNIT) - size_align = BITS_PER_UNIT; + if (flag_stack_usage_info && pstack_usage_size) + *pstack_usage_size += extra; + } /* Round the size to a multiple of the required stack alignment. Since the stack is presumed to be rounded before this allocation, |