Hi,
this patch fixes a few glitches in the post-reload compare elimination pass,
most notably the slightly disturbing opening comment:
This pass assumes:
[...]
(1) All comparison patterns are represented as
[(set (reg:CC) (compare:CC (reg) (immediate)))]
the mode mismatch in before_dom_children:
rtx x, flags = gen_rtx_REG (src_mode, targetm.flags_regnum);
/* Generate new comparison for substitution. */
x = gen_rtx_COMPARE (new_mode, XEXP (src, 0), XEXP (src, 1));
x = gen_rtx_SET (VOIDmode, flags, x);
and the direct tests on flag_non_call_exceptions:
if (flag_non_call_exceptions)
eh_note = find_reg_note (insn, REG_EH_REGION, NULL);
[...]
/* Take care that it's in the same EH region. */
if (flag_non_call_exceptions
&& !rtx_equal_p (eh_note, last_cmp->eh_note))
goto dont_delete;
It also factors out the comparison logic in before_dom_children to avoid the
series of gotos.
Tested on a private port we're about to submit, OK for the mainline?
2014-11-28 Eric Botcazou <ebotca...@adacore.com>
* compare-elim.c: Fix head comment.
(conforming_compare): Remove redundant test.
(can_eliminate_compare): New function extracted from...
(before_dom_children): ...here. Use it, replace direct uses of
flag_non_call_exceptions and tidy up.
(maybe_select_cc_mode): Tidy up.
--
Eric BotcazouIndex: compare-elim.c
===================================================================
--- compare-elim.c (revision 218133)
+++ compare-elim.c (working copy)
@@ -35,7 +35,7 @@ along with GCC; see the file COPYING3.
(1) All comparison patterns are represented as
- [(set (reg:CC) (compare:CC (reg) (immediate)))]
+ [(set (reg:CC) (compare:CC (reg) (reg_or_immediate)))]
(2) All insn patterns that modify the flags are represented as
@@ -157,7 +157,6 @@ conforming_compare (rtx_insn *insn)
return NULL;
if (REG_P (XEXP (src, 0))
- && REG_P (XEXP (src, 0))
&& (REG_P (XEXP (src, 1)) || CONSTANT_P (XEXP (src, 1))))
return src;
@@ -266,6 +265,45 @@ public:
virtual void before_dom_children (basic_block);
};
+/* Return true if conforming COMPARE with EH_NOTE is redundant with comparison
+ CMP and can thus be eliminated. */
+
+static bool
+can_eliminate_compare (rtx compare, rtx eh_note, struct comparison *cmp)
+{
+ /* Take care that it's in the same EH region. */
+ if (cfun->can_throw_non_call_exceptions
+ && !rtx_equal_p (eh_note, cmp->eh_note))
+ return false;
+
+ /* Make sure the compare is redundant with the previous. */
+ if (!rtx_equal_p (XEXP (compare, 0), cmp->in_a)
+ || !rtx_equal_p (XEXP (compare, 1), cmp->in_b))
+ return false;
+
+ /* New mode must be compatible with the previous compare mode. */
+ enum machine_mode new_mode
+ = targetm.cc_modes_compatible (GET_MODE (compare), cmp->orig_mode);
+
+ if (new_mode == VOIDmode)
+ return false;
+
+ if (cmp->orig_mode != new_mode)
+ {
+ /* Generate new comparison for substitution. */
+ rtx flags = gen_rtx_REG (new_mode, targetm.flags_regnum);
+ rtx x = gen_rtx_COMPARE (new_mode, cmp->in_a, cmp->in_b);
+ x = gen_rtx_SET (VOIDmode, flags, x);
+
+ if (!validate_change (cmp->insn, &PATTERN (cmp->insn), x, false))
+ return false;
+
+ cmp->orig_mode = new_mode;
+ }
+
+ return true;
+}
+
/* Identify comparison instructions within BB. If the flags from the last
compare in the BB is live at the end of the block, install the compare
in BB->AUX. Called via dom_walker.walk (). */
@@ -317,62 +355,26 @@ find_comparison_dom_walker::before_dom_c
src = conforming_compare (insn);
if (src)
{
- machine_mode src_mode = GET_MODE (src);
rtx eh_note = NULL;
- if (flag_non_call_exceptions)
+ if (cfun->can_throw_non_call_exceptions)
eh_note = find_reg_note (insn, REG_EH_REGION, NULL);
- if (!last_cmp_valid)
- goto dont_delete;
-
- /* Take care that it's in the same EH region. */
- if (flag_non_call_exceptions
- && !rtx_equal_p (eh_note, last_cmp->eh_note))
- goto dont_delete;
-
- /* Make sure the compare is redundant with the previous. */
- if (!rtx_equal_p (last_cmp->in_a, XEXP (src, 0))
- || !rtx_equal_p (last_cmp->in_b, XEXP (src, 1)))
- goto dont_delete;
-
- /* New mode must be compatible with the previous compare mode. */
- {
- machine_mode new_mode
- = targetm.cc_modes_compatible (last_cmp->orig_mode, src_mode);
- if (new_mode == VOIDmode)
- goto dont_delete;
-
- if (new_mode != last_cmp->orig_mode)
- {
- rtx x, flags = gen_rtx_REG (src_mode, targetm.flags_regnum);
-
- /* Generate new comparison for substitution. */
- x = gen_rtx_COMPARE (new_mode, XEXP (src, 0), XEXP (src, 1));
- x = gen_rtx_SET (VOIDmode, flags, x);
-
- if (!validate_change (last_cmp->insn,
- &PATTERN (last_cmp->insn), x, false))
- goto dont_delete;
-
- last_cmp->orig_mode = new_mode;
- }
- }
-
- /* All tests and substitutions succeeded! */
- if (eh_note)
- need_purge = true;
- delete_insn (insn);
- continue;
+ if (last_cmp_valid && can_eliminate_compare (src, eh_note, last_cmp))
+ {
+ if (eh_note)
+ need_purge = true;
+ delete_insn (insn);
+ continue;
+ }
- dont_delete:
last_cmp = XCNEW (struct comparison);
last_cmp->insn = insn;
last_cmp->prev_clobber = last_clobber;
last_cmp->in_a = XEXP (src, 0);
last_cmp->in_b = XEXP (src, 1);
last_cmp->eh_note = eh_note;
- last_cmp->orig_mode = src_mode;
+ last_cmp->orig_mode = GET_MODE (src);
all_compares.safe_push (last_cmp);
/* It's unusual, but be prepared for comparison patterns that
@@ -391,7 +393,6 @@ find_comparison_dom_walker::before_dom_c
/* In either case, the previous compare is no longer valid. */
last_cmp = NULL;
last_cmp_valid = false;
- continue;
}
/* Notice if this instruction uses the flags register. */
@@ -425,8 +426,7 @@ find_comparison_dom_walker::before_dom_c
FOR_EACH_EDGE (e, ei, bb->succs)
{
basic_block dest = e->dest;
- if (bitmap_bit_p (df_get_live_in (bb),
- targetm.flags_regnum)
+ if (bitmap_bit_p (df_get_live_in (bb), targetm.flags_regnum)
&& !single_pred_p (dest))
{
last_cmp->missing_uses = true;
@@ -498,8 +498,7 @@ maybe_select_cc_mode (struct comparison
sel_mode = SELECT_CC_MODE (cmp->uses[0].code, a, b);
for (i = 1; i < n; ++i)
{
- machine_mode new_mode;
- new_mode = SELECT_CC_MODE (cmp->uses[i].code, a, b);
+ machine_mode new_mode = SELECT_CC_MODE (cmp->uses[i].code, a, b);
if (new_mode != sel_mode)
{
sel_mode = targetm.cc_modes_compatible (sel_mode, new_mode);
@@ -507,7 +506,7 @@ maybe_select_cc_mode (struct comparison
return NULL;
}
}
-
+
if (sel_mode != cmp->orig_mode)
{
flags = gen_rtx_REG (sel_mode, targetm.flags_regnum);
@@ -633,7 +632,7 @@ try_eliminate_compare (struct comparison
validate_change (insn, &XVECEXP (PATTERN (insn), 0, 1), x, true);
if (!apply_change_group ())
return false;
-
+
/* Success. Delete the compare insn... */
delete_insn (cmp->insn);
