Add a hook to support telling the mid-end when to probe the stack

Programming / Compilers / GCC - tnfchris [138bc75d-0d04-0410-961f-82ee72b054a4] - 1 October 2018 12:58 EDT

This patch adds a hook to tell the mid-end about the probing requirements of the target. On AArch64 we allow a specific range for which no probing needs to be done. This same range is also the amount that will have to be probed up when a probe is needed after dropping the stack.

Defining this probe comes with the extra requirement that the outgoing arguments size of any function that uses alloca and stack clash be at the very least 8 bytes. With this invariant we can skip doing the zero checks for alloca and save some code.

A simplified version of the AArch64 stack frame is:

+-----------------------+ | | | | | | +-----------------------+ |LR | +-----------------------+ |FP | +-----------------------+ |dynamic allocations | -\ probe range hook effects these +-----------------------+ --\ and ensures that outgoing stack |padding | -- args is always > 8 when alloca. +-----------------------+ ---/ Which means it's always safe to probe |outgoing stack args |-/ at SP +-----------------------+


This allows us to generate better code than without the hook without affecting other targets.

With this patch I am also removing the stack_clash_protection_final_dynamic_probe hook which was added specifically for AArch64 but that is no longer needed.

gcc/

PR target/86486
- explow.c (anti_adjust_stack_and_probe_stack_clash): Support custom probe ranges.
- target.def (stack_clash_protection_alloca_probe_range): New. (stack_clash_protection_final_dynamic_probe): Remove.
- targhooks.h (default_stack_clash_protection_alloca_probe_range) New. (default_stack_clash_protection_final_dynamic_probe): Remove.
- targhooks.c: Likewise.
- doc/tm.texi.in (TARGET_STACK_CLASH_PROTECTION_ALLOCA_PROBE_RANGE): New. (TARGET_STACK_CLASH_PROTECTION_FINAL_DYNAMIC_PROBE): Remove.
- doc/tm.texi: Regenerate.

6b2ca3ef74a Add a hook to support telling the mid-end when to probe the stack.
gcc/ChangeLog | 14 ++++++++
gcc/doc/tm.texi | 8 +++--
gcc/doc/tm.texi.in | 2 +-
gcc/explow.c | 95 ++++++++++++++++++++++++++++++++----------------------
gcc/target.def | 15 ++++++---
gcc/targhooks.c | 6 ++--
gcc/targhooks.h | 2 +-
7 files changed, 93 insertions(+), 49 deletions(-)

Upstream: gcc.gnu.org


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