ping
From: Wilco Dijkstra
Sent: 25 July 2017 14:58
To: GCC Patches; James Greenhalgh; Jeff Law
Cc: nd
Subject: [PATCH][AArch64] Simplify frame layout for stack probing
This patch makes some changes to the frame layout in order to simplify
stack probing. We want to use the save of LR as a probe in any non-leaf
function. With shrinkwrapping we may only save LR before a call, so it
is useful to define a fixed location in the callee-saves. So force LR at
the bottom of the callee-saves even with -fomit-frame-pointer.
Also remove a rarely used frame layout that saves the callee-saves first
with -fomit-frame-pointer.
OK for commit (and backport to GCC7)?
ChangeLog:
2017-07-25 Wilco Dijkstra <wdijk...@arm.com>
* config/aarch64/aarch64.c (aarch64_layout_frame):
Ensure LR is always stored at the bottom of the callee-saves.
Remove frame option which saves callee-saves at top of frame.
--
diff --git a/gcc/config/aarch64/aarch64.c b/gcc/config/aarch64/aarch64.c
index
b8a4160d9de8e689ccd26cb9f0ce046ee65e0ef4..3fc36ae28d18b9635480fd99f1fa7719267e66e4
100644
--- a/gcc/config/aarch64/aarch64.c
+++ b/gcc/config/aarch64/aarch64.c
@@ -2875,7 +2875,8 @@ aarch64_frame_pointer_required (void)
/* Mark the registers that need to be saved by the callee and calculate
the size of the callee-saved registers area and frame record (both FP
- and LR may be omitted). */
+ and LR may be omitted). If the function is not a leaf, ensure LR is
+ saved at the bottom of the callee-save area. */
static void
aarch64_layout_frame (void)
{
@@ -2926,7 +2927,14 @@ aarch64_layout_frame (void)
cfun->machine->frame.wb_candidate1 = R29_REGNUM;
cfun->machine->frame.reg_offset[R30_REGNUM] = UNITS_PER_WORD;
cfun->machine->frame.wb_candidate2 = R30_REGNUM;
- offset += 2 * UNITS_PER_WORD;
+ offset = 2 * UNITS_PER_WORD;
+ }
+ else if (!crtl->is_leaf)
+ {
+ /* Ensure LR is saved at the bottom of the callee-saves. */
+ cfun->machine->frame.reg_offset[R30_REGNUM] = 0;
+ cfun->machine->frame.wb_candidate1 = R30_REGNUM;
+ offset = UNITS_PER_WORD;
}
/* Now assign stack slots for them. */
@@ -3025,20 +3033,6 @@ aarch64_layout_frame (void)
cfun->machine->frame.final_adjust
= cfun->machine->frame.frame_size - cfun->machine->frame.callee_adjust;
}
- else if (!frame_pointer_needed
- && varargs_and_saved_regs_size < max_push_offset)
- {
- /* Frame with large local area and outgoing arguments (this pushes the
- callee-saves first, followed by the locals and outgoing area):
- stp reg1, reg2, [sp, -varargs_and_saved_regs_size]!
- stp reg3, reg4, [sp, 16]
- sub sp, sp, frame_size - varargs_and_saved_regs_size */
- cfun->machine->frame.callee_adjust = varargs_and_saved_regs_size;
- cfun->machine->frame.final_adjust
- = cfun->machine->frame.frame_size - cfun->machine->frame.callee_adjust;
- cfun->machine->frame.hard_fp_offset = cfun->machine->frame.callee_adjust;
- cfun->machine->frame.locals_offset = cfun->machine->frame.hard_fp_offset;
- }
else
{
/* Frame with large local area and outgoing arguments using frame
pointer:
