RE: [PATCH, combine] Try REG_EQUAL for nonzero_bits

[Zhenqiang Chen]

> -----Original Message-----
> From: gcc-patches-ow...@gcc.gnu.org [mailto:gcc-patches-
> ow...@gcc.gnu.org] On Behalf Of Eric Botcazou
> Sent: Monday, November 24, 2014 5:41 PM
> To: Zhenqiang Chen
> Cc: gcc-patches@gcc.gnu.org
> Subject: Re: [PATCH, combine] Try REG_EQUAL for nonzero_bits
> 
> > Thanks for the comments. I will compare the two nonzero_bits from src
> > and REG_EQUAL. Then select the smaller one.
> 
> They are masks so you can simply AND them before ORing the result.
> 
> > Do you know why it use " SET_SRC (set)" other than "src" for
> > num_sign_bit_copies?
> >
> > If it is "src", I should do the same for num_sign_bit_copies with 
> > REG_EQUAL info.
> 
> Probably historical reasons, let's not try to change that now.  You can
apply
> the same treatment to num_sign_bit_copies (you will need a comparison
> here) while preserving the "src" vs "SET_SRC (set)" discrepancy.

Thanks for the comments. Patch is updated.

diff --git a/gcc/combine.c b/gcc/combine.c
index 1808f97..2e865d7 100644
--- a/gcc/combine.c
+++ b/gcc/combine.c
@@ -1603,6 +1603,28 @@ setup_incoming_promotions (rtx_insn *first)
     }
 }
 
+/* Update RSP from INSN's REG_EQUAL note and SRC.  */
+
+static void
+update_rsp_from_reg_equal (reg_stat_type *rsp, rtx_insn *insn, rtx src, rtx
x)
+{
+  rtx reg_equal = insn ? find_reg_equal_equiv_note (insn) : NULL_RTX;
+  unsigned HOST_WIDE_INT bits = nonzero_bits (src, nonzero_bits_mode);
+
+  if (reg_equal)
+    {
+      unsigned int num = num_sign_bit_copies (XEXP (reg_equal, 0),
+                                             GET_MODE (x));
+      bits &= nonzero_bits (XEXP (reg_equal, 0), nonzero_bits_mode);
+      rsp->nonzero_bits |= bits;
+
+      if (rsp->sign_bit_copies > num)
+       rsp->sign_bit_copies = num;
+    }
+  else
+    rsp->nonzero_bits |= bits;
+}
+
 /* Called via note_stores.  If X is a pseudo that is narrower than
    HOST_BITS_PER_WIDE_INT and is being set, record what bits are known
zero.
 
@@ -1698,13 +1720,14 @@ set_nonzero_bits_and_sign_copies (rtx x, const_rtx
set, void *data)
            src = GEN_INT (INTVAL (src) | ~GET_MODE_MASK (GET_MODE (x)));
 #endif
 
-         /* Don't call nonzero_bits if it cannot change anything.  */
-         if (rsp->nonzero_bits != ~(unsigned HOST_WIDE_INT) 0)
-           rsp->nonzero_bits |= nonzero_bits (src, nonzero_bits_mode);
          num = num_sign_bit_copies (SET_SRC (set), GET_MODE (x));
          if (rsp->sign_bit_copies == 0
              || rsp->sign_bit_copies > num)
            rsp->sign_bit_copies = num;
+
+         /* Don't call nonzero_bits if it cannot change anything.  */
+         if (rsp->nonzero_bits != ~(unsigned HOST_WIDE_INT) 0)
+           update_rsp_from_reg_equal (rsp, insn, src, x);
        }
       else
        {