combine: Fix split_i2i3 ICE [PR94291]

The following testcase ICEs on armv7hl-linux-gnueabi.
try_combine is called on:
(gdb) p debug_rtx (i3)
(insn 20 12 22 2 (set (mem/c:SI (plus:SI (reg/f:SI 102 sfp)
                (const_int -4 [0xfffffffffffffffc])) [1 x+0 S4 A32])
        (reg:SI 125)) "pr94291.c":7:8 241 {*arm_movsi_insn}
     (expr_list:REG_DEAD (reg:SI 125)
        (nil)))
(gdb) p debug_rtx (i2)
(insn 12 7 20 2 (parallel [
            (set (reg:CC 100 cc)
                (compare:CC (reg:SI 121 [ <retval> ])
                    (const_int 0 [0])))
            (set (reg:SI 125)
                (reg:SI 121 [ <retval> ]))
        ]) "pr94291.c":7:8 248 {*movsi_compare0}
     (expr_list:REG_UNUSED (reg:CC 100 cc)
        (nil)))
and tries to recognize cc = r121 cmp 0; [sfp-4] = r121 parallel,
but that isn't recognized, so it splits it into two: split_i2i3
[sfp-4] = r121 followed by cc = r121 cmp 0 which is recognized, but
ICEs because the code below insist that the SET_DEST of newi2pat
(or first set in PARALLEL thereof) must be a REG or SUBREG of REG,
but it is a MEM in this case.  I don't see any condition that would
guarantee that, perhaps for the swap_i2i3 case it was somehow guaranteed.

As the code just wants to update LOG_LINKS and LOG_LINKS are only for
registers, not for MEM or anything else, the patch just doesn't update those
if it isn't a REG or SUBREG of REG.

2020-04-07  Jakub Jelinek  <jakub@redhat.com>

	PR rtl-optimization/94291
	PR rtl-optimization/84169
	* combine.c (try_combine): For split_i2i3, don't assume SET_DEST
	must be a REG or SUBREG of REG; if it is not one of these, don't
	update LOG_LINKs.

	* gcc.dg/pr94291.c: New test.

4 files changed, 51 insertions, 19 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index a1ab9fb..12803e9 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,11 @@
+2020-04-07  Jakub Jelinek  <jakub@redhat.com>
+
+	PR rtl-optimization/94291
+	PR rtl-optimization/84169
+	* combine.c (try_combine): For split_i2i3, don't assume SET_DEST
+	must be a REG or SUBREG of REG; if it is not one of these, don't
+	update LOG_LINKs.
+
 2020-04-07  Richard Biener  <rguenther@suse.de>
 
 	PR middle-end/94479
diff --git a/gcc/combine.c b/gcc/combine.c
index 58366a6..cff76cd 100644
--- a/gcc/combine.c
+++ b/gcc/combine.c
@@ -4351,25 +4351,29 @@ try_combine (rtx_insn *i3, rtx_insn *i2, rtx_insn *i1, rtx_insn *i0,
       if (GET_CODE (x) == PARALLEL)
 	x = XVECEXP (newi2pat, 0, 0);
 
-      /* It can only be a SET of a REG or of a SUBREG of a REG.  */
-      unsigned int regno = reg_or_subregno (SET_DEST (x));
-
-      bool done = false;
-      for (rtx_insn *insn = NEXT_INSN (i3);
-	   !done
-	   && insn
-	   && NONDEBUG_INSN_P (insn)
-	   && BLOCK_FOR_INSN (insn) == this_basic_block;
-	   insn = NEXT_INSN (insn))
-	{
-	  struct insn_link *link;
-	  FOR_EACH_LOG_LINK (link, insn)
-	    if (link->insn == i3 && link->regno == regno)
-	      {
-		link->insn = i2;
-		done = true;
-		break;
-	      }
+      if (REG_P (SET_DEST (x))
+	  || (GET_CODE (SET_DEST (x)) == SUBREG
+	      && REG_P (SUBREG_REG (SET_DEST (x)))))
+	{
+	  unsigned int regno = reg_or_subregno (SET_DEST (x));
+
+	  bool done = false;
+	  for (rtx_insn *insn = NEXT_INSN (i3);
+	       !done
+	       && insn
+	       && NONDEBUG_INSN_P (insn)
+	       && BLOCK_FOR_INSN (insn) == this_basic_block;
+	       insn = NEXT_INSN (insn))
+	    {
+	      struct insn_link *link;
+	      FOR_EACH_LOG_LINK (link, insn)
+		if (link->insn == i3 && link->regno == regno)
+		  {
+		    link->insn = i2;
+		    done = true;
+		    break;
+		  }
+	    }
 	}
     }
 
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 71b5a14..3cbf891 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,9 @@
+2020-04-07  Jakub Jelinek  <jakub@redhat.com>
+
+	PR rtl-optimization/94291
+	PR rtl-optimization/84169
+	* gcc.dg/pr94291.c: New test.
+
 2020-04-07  Richard Biener  <rguenther@suse.de>
 
 	PR middle-end/94479
diff --git a/gcc/testsuite/gcc.dg/pr94291.c b/gcc/testsuite/gcc.dg/pr94291.c
new file mode 100644
index 0000000..7daa2b0
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr94291.c
@@ -0,0 +1,14 @@
+/* PR rtl-optimization/94291 */
+/* { dg-do compile } */
+/* { dg-options "-Og" } */
+
+unsigned a;
+
+unsigned
+foo (void)
+{
+  unsigned x
+    = (__builtin_sub_overflow ((long long) a, 0, &x)
+       ? 1 : (__INTPTR_TYPE__) __builtin_memmove (&x, foo, 1));
+  return a;
+}