On 9/25/26 09:56, Oleg Tolmatcev wrote:
ср, 23 сент. 2026 г. в 11:21, Richard Biener <[email protected]>:
On Wed, 16 Sep 2026, Oleg Tolmatcev wrote:
Targets that cannot guarantee arbitrary stack alignment cap stack slots at
MAX_SUPPORTED_STACK_ALIGNMENT. Win64 SEH caps MAX_STACK_ALIGNMENT at 128
bits; aarch64 does not define MAX_STACK_ALIGNMENT and is capped at
STACK_BOUNDARY, also 128 bits. assign_stack_local silently ignored any
alignment beyond that cap.
A 256-bit vector requires 32-byte alignment, but its slot could therefore
receive only 16-byte alignment while later MEM attributes still claimed 32.
x86 could select vmovaps from that MEM_ALIGN and fault on the under-aligned
slot (PR54412, MSYS2/MINGW-packages#1209). An escaped pointer has the same
problem even when the local move is unaligned, since its type still promises
the callee a 32-byte-aligned object.
Make assign_stack_local_1 honour an explicit alignment beyond the cap by
reserving enough space and aligning an address inside it at run time, as
assign_parm_setup_block already did for BLKmode parameters and
expand_stack_vars does for locals. Base the extra space on the alignment
guaranteed for VIRTUAL_STACK_VARS_REGNUM rather than on the maximum alignment
supported by the backend, since the frame itself is not guaranteed to have
the latter alignment on all targets.
Let a new internal assign_stack_local_2 return the address before run-time
alignment. Store it in the temp slot and realign the address on reuse, while
avoiding splitting or combining over-aligned slots.
Honour required temporary alignment at run time, but cap merely preferred
alignment. Preserve zero-size behavior and the target's preferred stack
boundary, and emit run-time alignment only during expansion to RTL.
Use ASLK_REDUCE_ALIGN where less alignment is acceptable: LRA spill slots and
the deliberately over-aligned SJLJ function context.
Regtested on x86_64-pc-linux-gnu and, under QEMU, on
aarch64-unknown-linux-gnu, with no new failures.
Thanks a lot, this is OK for trunk.
Thanks,
Richard.
Thanks a lot for the review. I don't have commit access by the way.
Oleg
Pushed to master branch, thanks for the patches and reviews.
