Re: [PATCH] Keep REG_INC note in subreg2 pass

[Jeff Law]

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?




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.

Jeff