After the m68k cc0 conversion, there is one code quality regression that
I can see: we no longer generate autoinc addressing modes in
comparisons. This is because the parts of the compiler that generate
autoinc are unwilling to substitute into jumps.
If you look at the code in reload, you'll see that it's careful around
jumps at find_reload time, and the code to perform autoinc reloads does
try to put all the extra code before the instruction. LRA seems to have
copied most of that code.
Also, in the former cc0 reality, a compare wasn't really any different
from a jump on m68k: we can't have a reload after the instruction in
either case. Any kind of move or arithmetic would clobber the flags.
That leads me to believe that there is no issue with autoinc in jumps,
hence this patch. Bootstrapped and tested on the gcc135 machine
(powerpc64le-unknown-linux-gnu). I don't really expect this to get
approved; alternatively I could write some peepholes which would
generate the same code as long as register pressure doesn't get too high.
Bernd
* auto-inc-dec.c (merge_in_block): Allow jumps.
* combine.c (can_combine_p): Allow jumps in autoinc.
diff --git a/gcc/auto-inc-dec.c b/gcc/auto-inc-dec.c
index bdb6efa..6dab135 100644
--- a/gcc/auto-inc-dec.c
+++ b/gcc/auto-inc-dec.c
@@ -1441,10 +1441,11 @@ merge_in_block (int max_reg, basic_block bb)
continue;
}
- /* This continue is deliberate. We do not want the uses of the
- jump put into reg_next_use because it is not considered safe to
- combine a preincrement with a jump. */
- if (JUMP_P (insn))
+ /* We used to skip jump insns, but both reload and LRA seem to
+ take precautions not to perform autoinc reloads after a jump or
+ a comparison. Allow them for regular autoinc only (for test
+ coverage reasons more than anything). */
+ if ((HAVE_PRE_MODIFY_REG || HAVE_POST_MODIFY_REG) && JUMP_P (insn))
continue;
if (dump_file)
diff --git a/gcc/combine.c b/gcc/combine.c
index 857ea30..e9e1464 100644
--- a/gcc/combine.c
+++ b/gcc/combine.c
@@ -2119,15 +2118,12 @@ can_combine_p (rtx_insn *insn, rtx_insn *i3, rtx_insn *pred ATTRIBUTE_UNUSED,
/* If INSN contains an autoincrement or autodecrement, make sure that
register is not used between there and I3, and not already used in
- I3 either. Neither must it be used in PRED or SUCC, if they exist.
- Also insist that I3 not be a jump; if it were one
- and the incremented register were spilled, we would lose. */
+ I3 either. Neither must it be used in PRED or SUCC, if they exist. */
if (AUTO_INC_DEC)
for (link = REG_NOTES (insn); link; link = XEXP (link, 1))
if (REG_NOTE_KIND (link) == REG_INC
- && (JUMP_P (i3)
- || reg_used_between_p (XEXP (link, 0), insn, i3)
+ && (reg_used_between_p (XEXP (link, 0), insn, i3)
|| (pred != NULL_RTX
&& reg_overlap_mentioned_p (XEXP (link, 0), PATTERN (pred)))
|| (pred2 != NULL_RTX
