[Bug target/65416] xtensa: memory allocated by alloca is used before the stack pointer is updated

[jcmvbkbc at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65416

--- Comment #7 from jcmvbkbc at gcc dot gnu.org ---
Author: jcmvbkbc
Date: Tue Jun 19 21:08:46 2018
New Revision: 261765

URL: https://gcc.gnu.org/viewcvs?rev=261765&root=gcc&view=rev
Log:
xtensa: fix PR target/65416

The issue is caused by reordering of stack pointer update after stack
space allocation with instructions that write to the allocated stack
space. In windowed ABI register spill area for the previous call frame
is located just below the stack pointer and may be reloaded back into
the register file on movsp.
Implement allocate_stack pattern for windowed ABI configuration and
insert an instruction that prevents reordering of frame memory access
and stack pointer update.

gcc/
2018-06-19  Max Filippov  <jcmvbkbc@gmail.com>

        Backport from mainline
        2018-06-19  Max Filippov  <jcmvbkbc@gmail.com>

        * config/xtensa/xtensa.md (UNSPEC_FRAME_BLOCKAGE): New unspec
        constant.
        (allocate_stack, frame_blockage, *frame_blockage): New patterns.


Modified:
    branches/gcc-6-branch/gcc/ChangeLog
    branches/gcc-6-branch/gcc/config/xtensa/xtensa.md