> Here is an alternative, almost completely untested, patch, which
> uses DW_OP_fbreg <N> for the arguments of dynamically realigned functions.
> draptest.c now works...
Thanks for the tip. I completely overlooked this CFA-based machinery and now
agree that it's the most sensible approach. For my defense, I would point out
that it's quite lightly documented. :-) I've attached a patch that adds a
blurb about it (as well as contains the fp_cfa_offset adjustment we both have
in our patches). I'll install it as obvious if you don't have any objection.
Now on to a few questions:
> 2011-05-23 Jakub Jelinek <ja...@redhat.com>
>
> * var-tracking.c (vt_add_function_parameter): Remap incoming
> MEMs with crtl->args.internal_arg_pointer based address
> if stack_realign_drap to arg_pointer_rtx.
> (vt_init_cfa_base): Add equate argument, don't equate cfa_base_rtx
> to hfp/sp if it is false.
> (vt_initialize): Adjust vt_init_cfa_base callers, don't call
> vt_init_cfa_base if frame_pointer_needed, but fp_cfa_offset is -1,
> set fp_cfa_offset to -1 if fp/argp hasn't been eliminated.
Why setting CFA_BASE_RTX here? The remapping in vt_add_function_parameter
doesn't seem to need it. Is that necessary so that the processing of MEMs is
short-circuited elsewhere? If so, would this be correct in the whole function
given that the MEMs aren't adjusted in this case (i.e. compute_cfa_pointer is
never called)?
* var-tracking.c (compute_cfa_pointer): Adjust head comment.
(vt_initialize): Set PROLOGUE_BB unconditionally.
Add block comment about CFA_BASE_RTX machinery.
Reset FP_CFA_OFFSET to -1 on all invalid paths.
Call vt_init_cfa_base only if FP_CFA_OFFSET isn't equal to -1.
--
Eric Botcazou
Index: var-tracking.c
===================================================================
--- var-tracking.c (revision 174058)
+++ var-tracking.c (working copy)
@@ -705,7 +705,8 @@ vt_stack_adjustments (void)
static rtx cfa_base_rtx;
static HOST_WIDE_INT cfa_base_offset;
-/* Compute a CFA-based value for the stack pointer. */
+/* Compute a CFA-based value for an ADJUSTMENT made to stack_pointer_rtx
+ or hard_frame_pointer_rtx. */
static inline rtx
compute_cfa_pointer (HOST_WIDE_INT adjustment)
@@ -8664,7 +8665,7 @@ vt_init_cfa_base (void)
static bool
vt_initialize (void)
{
- basic_block bb, prologue_bb = NULL;
+ basic_block bb, prologue_bb = single_succ (ENTRY_BLOCK_PTR);
HOST_WIDE_INT fp_cfa_offset = -1;
alloc_aux_for_blocks (sizeof (struct variable_tracking_info_def));
@@ -8722,6 +8723,15 @@ vt_initialize (void)
CLEAR_HARD_REG_SET (argument_reg_set);
+ /* In order to shield ourselves from adjustments to the stack pointer or to
+ the hard frame pointer that aren't meant to change the base location of
+ variables, we're going to rewrite MEMs based on them into MEMs based on
+ the CFA by de-eliminating stack_pointer_rtx or hard_frame_pointer_rtx to
+ the virtual CFA pointer frame_pointer_rtx resp. arg_pointer_rtx. We can
+ do this either when there is no frame pointer in the function and stack
+ adjustments are consistent for all basic blocks or when there is a frame
+ pointer and no stack realignment. In any case, we first have to check
+ that frame_pointer_rtx resp. arg_pointer_rtx has been eliminated. */
if (!frame_pointer_needed)
{
rtx reg, elim;
@@ -8764,10 +8774,11 @@ vt_initialize (void)
}
if (elim != hard_frame_pointer_rtx)
fp_cfa_offset = -1;
- else
- prologue_bb = single_succ (ENTRY_BLOCK_PTR);
}
+ else
+ fp_cfa_offset = -1;
}
+
if (frame_pointer_needed)
{
rtx insn;
@@ -8870,7 +8881,8 @@ vt_initialize (void)
if (bb == prologue_bb
&& hard_frame_pointer_adjustment == -1
&& RTX_FRAME_RELATED_P (insn)
- && fp_setter (insn))
+ && fp_setter (insn)
+ && fp_cfa_offset != -1)
{
vt_init_cfa_base ();
hard_frame_pointer_adjustment = fp_cfa_offset;
