Re: [PATCH] Keep REG_INC note in subreg2 pass

[Jeff Law]

On 10/30/13 00:09, Zhenqiang Chen wrote:
On 30 October 2013 02:47, Jeff Law <l...@redhat.com> wrote:
On 10/24/13 02:20, Zhenqiang Chen wrote:

Hi,

REG_INC note is lost in subreg2 pass when resolve_simple_move, which
might lead to wrong dependence for ira. e.g. In function
validate_equiv_mem of ira.c, it checks REG_INC note:

       for (note = REG_NOTES (insn); note; note = XEXP (note, 1))
          if ((REG_NOTE_KIND (note) == REG_INC
               || REG_NOTE_KIND (note) == REG_DEAD)
              && REG_P (XEXP (note, 0))
              && reg_overlap_mentioned_p (XEXP (note, 0), memref))
            return 0;

Without REG_INC note, validate_equiv_mem will return a wrong result.

Referhttps://bugs.launchpad.net/gcc-linaro/+bug/1243022  for more

detail about a real case in kernel.

Bootstrap and no make check regression on X86-64 and ARM.

Is it OK for trunk and 4.8?

Thanks!
-Zhenqiang

ChangeLog:
2013-10-24  Zhenqiang Chen<zhenqiang.c...@linaro.org>

          * lower-subreg.c (resolve_simple_move): Copy REG_INC note.

testsuite/ChangeLog:
2013-10-24  Zhenqiang Chen<zhenqiang.c...@linaro.org>

          * gcc.target/arm/lp1243022.c: New test.

This clearly handles adding a note when the destination is a MEM with a side
effect.  What about cases where the side effect is associated with a load
from memory rather than a store to memory?

Yes. We should handle load from memory.



lp1243022.patch


diff --git a/gcc/lower-subreg.c b/gcc/lower-subreg.c
index 57b4b3c..e710fa5 100644
--- a/gcc/lower-subreg.c
+++ b/gcc/lower-subreg.c
@@ -1056,6 +1056,22 @@ resolve_simple_move (rtx set, rtx insn)
         mdest = simplify_gen_subreg (orig_mode, dest, GET_MODE (dest), 0);
         minsn = emit_move_insn (real_dest, mdest);

+#ifdef AUTO_INC_DEC
+      /* Copy the REG_INC notes.  */
+      if (MEM_P (real_dest) && !(resolve_reg_p (real_dest)
+                                || resolve_subreg_p (real_dest)))
+       {
+         rtx note = find_reg_note (insn, REG_INC, NULL_RTX);
+         if (note)
+           {
+             if (!REG_NOTES (minsn))
+               REG_NOTES (minsn) = note;
+             else
+               add_reg_note (minsn, REG_INC, note);
+           }
+       }
+#endif

If MINSN does not have any notes, then this results in MINSN and INSN
sharing the note.  Note carefully that notes are chained (see implementation
of add_reg_note).  Thus the sharing would result in MINSN and INSN actually
sharing a chain of notes.  I'm pretty sure that's not what you intended.  I
think you need to always use add_reg_note.

Yes. I should use add_reg_note.

Here is the updated patch:

diff --git a/gcc/lower-subreg.c b/gcc/lower-subreg.c
index ebf364f..16dfa62 100644
--- a/gcc/lower-subreg.c
+++ b/gcc/lower-subreg.c
@@ -967,7 +967,20 @@ resolve_simple_move (rtx set, rtx insn)
        rtx reg;

        reg = gen_reg_rtx (orig_mode);
+
+#ifdef AUTO_INC_DEC
+      {
+       rtx move = emit_move_insn (reg, src);
+       if (MEM_P (src))
+         {
+           rtx note = find_reg_note (insn, REG_INC, NULL_RTX);
+           if (note)
+             add_reg_note (move, REG_INC, XEXP (note, 0));
+         }
+      }
+#else
        emit_move_insn (reg, src);
+#endif
        src = reg;
      }

@@ -1057,6 +1070,16 @@ resolve_simple_move (rtx set, rtx insn)
         mdest = simplify_gen_subreg (orig_mode, dest, GET_MODE (dest), 0);
        minsn = emit_move_insn (real_dest, mdest);

+#ifdef AUTO_INC_DEC
+  if (MEM_P (real_dest) && !(resolve_reg_p (real_dest)
+                            || resolve_subreg_p (real_dest)))
Formatting nit.   This should be formatted as

if (MEM_P (real_dest)
    && !(resolve_reg_p (real_dest) || resolve_subreg_p (real_dest)))

If that results in too long of a line, then it should wrap like this:

if (MEM_P (real_dest)
    && !(resolve_reg_p (real_dest)
         || resolve_subreg_p (real_dest)))

OK with that change.  Please install on the trunk.  The 4.8 maintainers 
have the final call for the 4.8 release branch.

Thanks,
Jeff