I have several questions on this fix:
1. This fix avoided expanding “.DEFERRED_INIT” when !tree_fits_uhwi_p
(TYPE_SIZE_UNIT (var_type)).
As a result, this call to .DEFERRED_INIT will NOT be expanded at all.
Then not expanding .DEFERRED_INIT in RTL expanding phase will trigger more
issues in later RTL phases, this looks not correct to me. (Actually, with is
the patch, this testing case still failed in a later RTL stage).
So, If we really want to avoid auto-init for VLA vectors, we should not add
call to .DEFERRED_INIT in gimplification phase at all.
2. For the added .DEFERRED_INIT:
__SVFloat64_t f64;
f64 = .DEFERRED_INIT (POLY_INT_CST [16, 16], 2, 0);
What does “POLY_INT_CST[16,16]” mean? Is this a constant size? If YES, what’s
the value of it? If Not, can we use “memset” to expand it?
Thanks.
Qing
> On Oct 4, 2021, at 3:57 AM, Richard Biener via Gcc-patches
> <gcc-patches@gcc.gnu.org> wrote:
>
> This avoids ICEing for VLA vector auto-init by not initializing.
>
> Bootstrapped and tested on x86_64-unknown-linux-gnu, pushed.
>
> 2021-10-04 Richard Biener <rguent...@suse.de>
>
> PR middle-end/102587
> * internal-fn.c (expand_DEFERRED_INIT): Guard register
> initialization path an avoid initializing VLA registers
> with it.
>
> * gcc.target/aarch64/sve/pr102587-1.c: New testcase.
> * gcc.target/aarch64/sve/pr102587-2.c: Likewise.
> ---
> gcc/internal-fn.c | 3 ++-
> gcc/testsuite/gcc.target/aarch64/sve/pr102587-1.c | 4 ++++
> gcc/testsuite/gcc.target/aarch64/sve/pr102587-2.c | 4 ++++
> 3 files changed, 10 insertions(+), 1 deletion(-)
> create mode 100644 gcc/testsuite/gcc.target/aarch64/sve/pr102587-1.c
> create mode 100644 gcc/testsuite/gcc.target/aarch64/sve/pr102587-2.c
>
> diff --git a/gcc/internal-fn.c b/gcc/internal-fn.c
> index 8312d08aab2..ef5dc90db56 100644
> --- a/gcc/internal-fn.c
> +++ b/gcc/internal-fn.c
> @@ -3035,7 +3035,8 @@ expand_DEFERRED_INIT (internal_fn, gcall *stmt)
> /* Expand this memset call. */
> expand_builtin_memset (m_call, NULL_RTX, TYPE_MODE (var_type));
> }
> - else
> + /* ??? Deal with poly-int sized registers. */
> + else if (tree_fits_uhwi_p (TYPE_SIZE_UNIT (var_type)))
> {
> /* If this variable is in a register, use expand_assignment might
> generate better code. */
> diff --git a/gcc/testsuite/gcc.target/aarch64/sve/pr102587-1.c
> b/gcc/testsuite/gcc.target/aarch64/sve/pr102587-1.c
> new file mode 100644
> index 00000000000..2b9a68b0b59
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/aarch64/sve/pr102587-1.c
> @@ -0,0 +1,4 @@
> +/* { dg-do compile } */
> +/* { dg-options "-ftrivial-auto-var-init=zero" } */
> +
> +void foo() { __SVFloat64_t f64; }
> diff --git a/gcc/testsuite/gcc.target/aarch64/sve/pr102587-2.c
> b/gcc/testsuite/gcc.target/aarch64/sve/pr102587-2.c
> new file mode 100644
> index 00000000000..4cdb9056002
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/aarch64/sve/pr102587-2.c
> @@ -0,0 +1,4 @@
> +/* { dg-do compile } */
> +/* { dg-options "-ftrivial-auto-var-init=pattern" } */
> +
> +void foo() { __SVFloat64_t f64; }
> --
> 2.31.1
