Hi
As reported in bug pr62151, combine pass may wrongly delete necessary
instruction in function distribute_notes thus leaving register
uninitialized. This patch is to fix the issue by checking if i2 immediately
modifies the register in REG_DEAD note. If yes, set tem_insn accordingly to
start finding right place for note distribution from i2.
I once sent a RFC patch at
https://gcc.gnu.org/ml/gcc-patches/2014-08/msg01718.html, but got no
comments, here I added some comments in this patch to make it a formal one.
I tested the original patch, and will re-test it against the latest code
later. So is it OK? Any comments will be appreciated.
Thanks,
bin
2014-08-27 Bin Cheng <bin.ch...@arm.com>
PR rtl-optimization/62151
* combine.c (distribute_notes): Check i2 if it modifies register
in REG_DEAD note immediately, set tem_insn accordingly.Index: gcc/combine.c
===================================================================
--- gcc/combine.c (revision 214413)
+++ gcc/combine.c (working copy)
@@ -13499,7 +13499,38 @@ distribute_notes (rtx notes, rtx_insn *from_insn,
|| rtx_equal_p (XEXP (note, 0), elim_i1)
|| rtx_equal_p (XEXP (note, 0), elim_i0))
break;
- tem_insn = i3;
+
+ /* See PR62151.
+ It's possible to have below situation:
+ i0: r1 <- const_0
+ i1: r2 <- r1 op_1 const_1
+ REG_DEAD r1
+ i2: r1 <- r2 op_2 const_2
+ REG_DEAD r2
+ i3: r3 <- r1
+ i4: r4 <- r1
+
+ It is transformed into below code before distributing
+ the REG_DEAD note in i1:
+ i0: NOTE_INSN_DELETED
+ i1: NOTE_INSN_DELETED
+ i2: r1 <- const_combined
+ i3: r3 <- const_combined
+ i4: r4 <- r1
+
+ We need to check if i2 immediately modifies r1 otherwise
+ i2 would be deleted by below code when distributing
+ REG_DEAD note, leaving r1 in i4 uninitialied.
+
+ We set TEM_INSN to i2 for this case indicating that we
+ need to find right place for distribution from i2.
+ */
+ if (from_insn && i2
+ && from_insn != i2 && from_insn != i3
+ && reg_set_p (XEXP (note, 0), PATTERN (i2)))
+ tem_insn = i2;
+ else
+ tem_insn = i3;
}
if (place == 0)
