From: Ilya Leoshkevich <iii@linux.ibm.com>
Date: Tue, 8 Sep 2020 23:23:51 +0000 (+0200)
Subject: rtlanal: fix subreg handling in set_noop_p ()
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=d1a31689a736cdfb5e7cfa01f1168e338510e63b;p=gcc.git

rtlanal: fix subreg handling in set_noop_p ()

The following s390 rtx is errneously considered a no-op:

(set (subreg:DF (reg:TF %f0) 8) (subreg:DF (reg:V1TF %f0) 8))

Here, SET_DEST is a second register in a floating-point register pair,
and SET_SRC is the second half of a vector register, so they refer to
different bits.

Fix by treating subregs of registers in different modes conservatively.

gcc/ChangeLog:

2020-09-11  Ilya Leoshkevich  <iii@linux.ibm.com>

	* rtlanal.c (set_noop_p): Treat subregs of registers in
	different modes conservatively.
---

diff --git a/gcc/rtlanal.c b/gcc/rtlanal.c
index 5ae38b7966d..01130a10783 100644
--- a/gcc/rtlanal.c
+++ b/gcc/rtlanal.c
@@ -1619,6 +1619,10 @@ set_noop_p (const_rtx set)
 	return 0;
       src = SUBREG_REG (src);
       dst = SUBREG_REG (dst);
+      if (GET_MODE (src) != GET_MODE (dst))
+	/* It is hard to tell whether subregs refer to the same bits, so act
+	   conservatively and return 0.  */
+	return 0;
     }
 
   /* It is a NOOP if destination overlaps with selected src vector