> Am 03.01.2025 um 10:04 schrieb Richard Sandiford <richard.sandif...@arm.com>:
>
> This PR was about a case in which late-combine moved a stack
> deallocation across an earlier stack access. This was possible
> because the deallocation was missing the RTL-SSA equivalent of
> a vop, which in turn was because rtl_properties didn't treat
> the deallocation as writing to memory. I think the bug was
> ultimately there.
>
> Tested on x86_64-linux-gnu (which the PR was reported against)
> and aarch64-linux-gnu. OK to install?
Ok
> I don't think any earlier users of RTL-SSA are likely to be
> affected by this, so I'm not sure it's worth a backport.
Your call.
Richard
> Richard
>
>
> gcc/
> PR rtl-optimization/117938
> * rtlanal.cc (rtx_properties::try_to_add_dest): Treat writes
> to the stack pointer as also writing to memory.
>
> gcc/testsuite/
> PR rtl-optimization/117938
> * gcc.dg/torture/pr117938.c: New test.
> ---
> gcc/rtlanal.cc | 14 +++++++---
> gcc/testsuite/gcc.dg/torture/pr117938.c | 36 +++++++++++++++++++++++++
> 2 files changed, 47 insertions(+), 3 deletions(-)
> create mode 100644 gcc/testsuite/gcc.dg/torture/pr117938.c
>
> diff --git a/gcc/rtlanal.cc b/gcc/rtlanal.cc
> index e7efb48c398..8caffafdaa4 100644
> --- a/gcc/rtlanal.cc
> +++ b/gcc/rtlanal.cc
> @@ -2163,10 +2163,18 @@ rtx_properties::try_to_add_dest (const_rtx x,
> unsigned int flags)
>
> if (LIKELY (REG_P (x)))
> {
> - /* We want to keep sp alive everywhere - by making all
> - writes to sp also use sp. */
> if (REGNO (x) == STACK_POINTER_REGNUM)
> - flags |= rtx_obj_flags::IS_READ;
> + {
> + /* Stack accesses are dependent on previous allocations and
> + anti-dependent on later deallocations, so both types of
> + stack operation are akin to a memory write. */
> + if (ref_iter != ref_end)
> + *ref_iter++ = rtx_obj_reference (MEM_REGNO, flags, BLKmode);
> +
> + /* We want to keep sp alive everywhere - by making all
> + writes to sp also use sp. */
> + flags |= rtx_obj_flags::IS_READ;
> + }
> try_to_add_reg (x, flags);
> return;
> }
> diff --git a/gcc/testsuite/gcc.dg/torture/pr117938.c
> b/gcc/testsuite/gcc.dg/torture/pr117938.c
> new file mode 100644
> index 00000000000..5a3b6d2156c
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/torture/pr117938.c
> @@ -0,0 +1,36 @@
> +/* { dg-do run { target { int32 && int128 } } } */
> +/* { dg-additional-options "-Wno-psabi --param=max-cse-insns=1" } */
> +
> +typedef unsigned V __attribute__((__vector_size__(64)));
> +typedef unsigned __int128 W __attribute__((__vector_size__(64)));
> +unsigned a;
> +W b;
> +V c;
> +W d;
> +
> +__attribute__((__noinline__))
> +W
> +bar (unsigned u, V z, W w)
> +{
> + u *= z[5];
> + return u + w;
> +}
> +
> +W
> +foo (V v)
> +{
> + unsigned g = a ? 1 : -1;
> + v ^= 0 <= v;
> + v <<= ((V){ bar (0, c, b)[0] } & 1);
> + v >>= ((V){ g, bar (1, c, b)[0] } & 1);
> + return a + b + (W) v + d;
> +}
> +
> +int
> +main ()
> +{
> + V x = (V) foo ((V) { });
> + for (unsigned i = 0; i < sizeof(x)/sizeof(x[0]); i++)
> + if (x[i] != (i ? 0xffffffff : 0x7fffffff))
> + __builtin_abort();
> +}
> --
> 2.25.1
>
