> That is so that the argp (or framep) will be properly handled during
> CSELIB, as constant VALUE that is never changed through the function. And
> additionally to find out if we can do the replacement (we can't if argp
> resp. framep isn't eliminated and could therefore occur in the real code).
OK, thanks for the explanation.
> This comment is not 100% accurate. The reason we do that is to use the
> much more compact DW_OP_fbreg* if possible compared to huge location lists,
> especially for !frame_pointer_needed where the location list would need to
> have another entry whenever sp changes. dwarf2out.c rewrites argp/framep
> if eliminated into DW_OP_fbreg (with some offset when needed).
Adjusted.
> While I had part of this in my patch too, it is unnecessary, if prologue_bb
> is set to non-NULL only when we want to use it, then we know fp_cfa_offset
> is not -1. By computing prologue_bb always, it will call fp_setter
> unnecessarily for every insn in the prologue bb for !frame_pointer_needed
> or for DRAP. I guess adding a comment instead of this would be better.
The fp_cfa_offset != -1 was before the call to fp_setter in my first patch. :-)
Revised version attached.
--
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 +8723,16 @@ vt_initialize (void)
CLEAR_HARD_REG_SET (argument_reg_set);
+ /* In order to factor out the adjustments made to the stack pointer or to
+ the hard frame pointer and thus be able to use DW_OP_fbreg operations
+ instead of individual location lists, 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.
+ But 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 +8775,11 @@ 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;
@@ -8867,7 +8879,8 @@ vt_initialize (void)
VTI (bb)->out.stack_adjust += post;
}
- if (bb == prologue_bb
+ if (fp_cfa_offset != -1
+ && bb == prologue_bb
&& hard_frame_pointer_adjustment == -1
&& RTX_FRAME_RELATED_P (insn)
&& fp_setter (insn))
