[Bug middle-end/57955] [9/10/11/12 Regression] Uniquization of constants reduces alignment of initializers
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57955 --- Comment #26 from David Edelsohn --- As Bill mentioned, one can increase the alignment of a large constant, but there is no way for the hooks that set alignment to recognize that the constant will be assigned to variable with stricter alignment.
[Bug middle-end/57955] [9/10/11/12 Regression] Uniquization of constants reduces alignment of initializers
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57955
--- Comment #25 from Eric Botcazou ---
> Before the gimplification change the initializer {1,} was promoted to a
> static const and given an alignment of 128; due to this part of the code:
>
> if (align > DECL_ALIGN (new_tree))
> {
> DECL_ALIGN (new_tree) = align;
> DECL_USER_ALIGN (new_tree) = 1;
> }
>
> But now it just uses DATA_ALIGNMENT (the code should be using
> TARGET_CONSTANT_ALIGNMENT but does not right now, that was a proposal).
Yes, exactly. The initializer is put into the "tree" constant pool, where its
alignment is uniformly set to DATA_ALIGNMENT.
[Bug middle-end/57955] [9/10/11/12 Regression] Uniquization of constants reduces alignment of initializers
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57955
--- Comment #24 from Andrew Pinski ---
Just to summarize this bug as far as I read it, please correct me if I am
wrong; note I am not proposing a change, just trying to summarize the back and
forth since it is not obvious right away of what the problem was.
This was the testcase:
void foo(void)
{
int x[8] __attribute__((aligned(128))) = { 1, 1, 1, 1, 1, 1, 1, 1 };
bar (x);
}
Before the gimplification change the initializer {1,} was promoted to a
static const and given an alignment of 128; due to this part of the code:
if (align > DECL_ALIGN (new_tree))
{
DECL_ALIGN (new_tree) = align;
DECL_USER_ALIGN (new_tree) = 1;
}
But now it just uses DATA_ALIGNMENT (the code should be using
TARGET_CONSTANT_ALIGNMENT but does not right now, that was a proposal).
rs6000_constant_alignment (TARGET_CONSTANT_ALIGNMENT) only aligns strings csts
to word (32 or 64) aligned. rs6000_data_alignment (DATA_ALIGNMENT) only aligns
vectors to 128 and char arrays to word (32 or 64) align.
[Bug middle-end/57955] [9/10/11/12 Regression] Uniquization of constants reduces alignment of initializers
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57955 Richard Biener changed: What|Removed |Added Target Milestone|9.4 |9.5 --- Comment #23 from Richard Biener --- GCC 9.4 is being released, retargeting bugs to GCC 9.5.
[Bug middle-end/57955] [9/10/11/12 Regression] Uniquization of constants reduces alignment of initializers
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57955 Jakub Jelinek changed: What|Removed |Added Target Milestone|8.5 |9.4 --- Comment #22 from Jakub Jelinek --- GCC 8 branch is being closed.
