Re: [PATCH] Try to resolve paths in threader without looking further back.

[Aldy Hernandez <aldyh@redhat.com>]

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On Wed, Oct 20, 2021 at 10:19 PM Jeff Law <jeffreyalaw@gmail.com> wrote:
> So we want to keep some form of ssa-dom-thread-7.  That' s the canonical
> testcase for the case for the FSM optimization.
>
> What we need to verify is that we thread jumps across the backedge of
> the loop through the switch statement to a particular case (thus
> bypassing the indirect jump for the switch statement).  How to do that
> in a way that's easier to manage?  I have no clue.  I guess a gimple-fe
> based test might help.

Ah, I see.

After lots of pain, I was able to distill a tiny testcase that does
just that (tree-ssa/ssa-thread-backedge.c), and is easy to maintain.
I've added a "backedge" marker to the path dumping code for easy
matching in the test.  An alternative would be to convert it to a
gimple FE test examining the exact thread sequence through the
backedge, but I think that's overkill since the test is so small.

Phew, I think we're finally converging on a useful set of threading tests :).

OK for trunk?
Aldy

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From d6a3114b160079a60d968cd21950a33116361d75 Mon Sep 17 00:00:00 2001
From: Aldy Hernandez <aldyh@redhat.com>
Date: Wed, 20 Oct 2021 07:29:25 +0200
Subject: [PATCH] Try to resolve paths in threader without looking further
 back.

Sometimes we can solve a candidate path without having to recurse
further back.  This can mostly happen in fully resolving mode, because
we can ask the ranger what the range on entry to the path is, but
there's no reason this can't always apply.  This one-liner removes
the fully-resolving restriction.

I'm tickled pink to see how many things we now get quite early
in the compilation.  I actually had to disable jump threading entirely
for a few tests because the early threader was catching things
disturbingly early.  Also, as Richi predicted, I saw a lot of pre-VRP
cleanups happening.

I was going to commit this as obvious, but I think the test changes
merit discussion.

We've been playing games with gcc.dg/tree-ssa/ssa-thread-11.c for quite
some time.  Every time a threading pass gets smarter, we push the
check further down the pipeline.  We've officially run out of dumb
threading passes to disable ;-).  In the last year we've gone up from a
handful of threads, to 34 threads with the current combination of
options.  I doubt this is testing anything useful anymore, so I've
removed it.

Similarly for gcc.dg/tree-ssa/ssa-dom-thread-4.c.  We used to thread 3
jump threads, but they were disallowed because of loop rotation.  Then
we started catching more jump threads in VRP2 threading so we tested
there.  With this patch though, we triple the number of threads found
from 11 to 31.  I believe this test has outlived its usefulness, and
I've removed it.  Note that even though we have these outrageous
possibilities for this test, the block copier ultimately chops them
down (23 survive though).

The ssa-dom-thread-7.c is the canonical test for the FSM optimization,
but it has become a maintenance burden.  The number of threads has
been consistently growing over the years, and there's no clean way to
test that we're actually threading through the backedges.  I have
replaced this test with a much simpler one (ssa-thread-backedge.c)
that tests that we can thread across the backedge, through the switch
statement and into a particular case.

All in all, I believe the simpler jump threading tests, as well as the
gimple FE tests I've added, more than adequately cover us.

Tested on x86-64 Linux.

gcc/ChangeLog:

	* tree-ssa-threadbackward.c (back_threader::find_paths_to_names):
	Always try to resolve path without looking back.
	* tree-ssa-threadupdate.c (dump_jump_thread): Indidicate whether
	edge is a back edge.

gcc/testsuite/ChangeLog:

	* gcc.dg/graphite/scop-dsyr2k-2.c: Adjust for jump threading changes.
	* gcc.dg/graphite/scop-dsyr2k.c: Same.
	* gcc.dg/graphite/scop-dsyrk-2.c: Same.
	* gcc.dg/graphite/scop-dsyrk.c: Same.
	* gcc.dg/tree-ssa/pr20701.c: Same.
	* gcc.dg/tree-ssa/pr20702.c: Same.
	* gcc.dg/tree-ssa/pr21086.c: Same.
	* gcc.dg/tree-ssa/pr25382.c: Same.
	* gcc.dg/tree-ssa/pr58480.c: Same.
	* gcc.dg/tree-ssa/ssa-vrp-thread-1.c: Same.
	* gcc.dg/tree-ssa/vrp08.c: Same.
	* gcc.dg/tree-ssa/vrp55.c: Same.
	* gcc.dg/tree-ssa/ssa-dom-thread-4.c: Removed.
	* gcc.dg/tree-ssa/ssa-dom-thread-7.c: Removed.
	* gcc.dg/tree-ssa/ssa-thread-11.c: Removed.
	* gcc.dg/uninit-pr89230-1.c: xfail.
---
 gcc/testsuite/gcc.dg/graphite/scop-dsyr2k-2.c |   1 +
 gcc/testsuite/gcc.dg/graphite/scop-dsyr2k.c   |   1 +
 gcc/testsuite/gcc.dg/graphite/scop-dsyrk-2.c  |   1 +
 gcc/testsuite/gcc.dg/graphite/scop-dsyrk.c    |   1 +
 gcc/testsuite/gcc.dg/tree-ssa/pr20701.c       |   2 +-
 gcc/testsuite/gcc.dg/tree-ssa/pr20702.c       |   2 +-
 gcc/testsuite/gcc.dg/tree-ssa/pr21086.c       |   2 +-
 gcc/testsuite/gcc.dg/tree-ssa/pr25382.c       |   2 +-
 gcc/testsuite/gcc.dg/tree-ssa/pr58480.c       |   2 +-
 .../gcc.dg/tree-ssa/ssa-dom-thread-4.c        |  60 --------
 .../gcc.dg/tree-ssa/ssa-dom-thread-7.c        | 134 ------------------
 gcc/testsuite/gcc.dg/tree-ssa/ssa-thread-11.c |  50 -------
 .../gcc.dg/tree-ssa/ssa-thread-backedge.c     |  32 +++++
 .../gcc.dg/tree-ssa/ssa-vrp-thread-1.c        |   4 +-
 gcc/testsuite/gcc.dg/tree-ssa/vrp08.c         |   2 +-
 gcc/testsuite/gcc.dg/tree-ssa/vrp55.c         |   6 +-
 gcc/testsuite/gcc.dg/uninit-pr89230-1.c       |   3 +-
 gcc/tree-ssa-threadbackward.c                 |   4 +-
 gcc/tree-ssa-threadupdate.c                   |   3 +
 19 files changed, 54 insertions(+), 258 deletions(-)
 delete mode 100644 gcc/testsuite/gcc.dg/tree-ssa/ssa-dom-thread-4.c
 delete mode 100644 gcc/testsuite/gcc.dg/tree-ssa/ssa-dom-thread-7.c
 delete mode 100644 gcc/testsuite/gcc.dg/tree-ssa/ssa-thread-11.c
 create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/ssa-thread-backedge.c

diff --git a/gcc/testsuite/gcc.dg/graphite/scop-dsyr2k-2.c b/gcc/testsuite/gcc.dg/graphite/scop-dsyr2k-2.c
index 06aa19a8577..42e23fc157e 100644
--- a/gcc/testsuite/gcc.dg/graphite/scop-dsyr2k-2.c
+++ b/gcc/testsuite/gcc.dg/graphite/scop-dsyr2k-2.c
@@ -1,4 +1,5 @@
 /* { dg-require-effective-target size32plus } */
+/* { dg-additional-options "-fno-thread-jumps" } */
 #define NMAX 3000
 
 static double a[NMAX][NMAX], b[NMAX][NMAX], c[NMAX][NMAX];
diff --git a/gcc/testsuite/gcc.dg/graphite/scop-dsyr2k.c b/gcc/testsuite/gcc.dg/graphite/scop-dsyr2k.c
index 41c91b97b57..feb99358ac7 100644
--- a/gcc/testsuite/gcc.dg/graphite/scop-dsyr2k.c
+++ b/gcc/testsuite/gcc.dg/graphite/scop-dsyr2k.c
@@ -1,4 +1,5 @@
 /* { dg-require-effective-target size32plus } */
+/* { dg-additional-options "-fno-thread-jumps" } */
 #define NMAX 3000
 
 static double a[NMAX][NMAX], b[NMAX][NMAX], c[NMAX][NMAX];
diff --git a/gcc/testsuite/gcc.dg/graphite/scop-dsyrk-2.c b/gcc/testsuite/gcc.dg/graphite/scop-dsyrk-2.c
index 5622dce4798..935ade3fb6e 100644
--- a/gcc/testsuite/gcc.dg/graphite/scop-dsyrk-2.c
+++ b/gcc/testsuite/gcc.dg/graphite/scop-dsyrk-2.c
@@ -1,4 +1,5 @@
 /* { dg-require-effective-target size32plus } */
+/* { dg-additional-options "-fno-thread-jumps" } */
 #define NMAX 3000
 #define MEASURE_TIME 1
 
diff --git a/gcc/testsuite/gcc.dg/graphite/scop-dsyrk.c b/gcc/testsuite/gcc.dg/graphite/scop-dsyrk.c
index e01a517be11..5c65e406589 100644
--- a/gcc/testsuite/gcc.dg/graphite/scop-dsyrk.c
+++ b/gcc/testsuite/gcc.dg/graphite/scop-dsyrk.c
@@ -1,4 +1,5 @@
 /* { dg-require-effective-target size32plus } */
+/* { dg-additional-options "-fno-thread-jumps" } */
 #define NMAX 3000
 #define MEASURE_TIME 1
 
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr20701.c b/gcc/testsuite/gcc.dg/tree-ssa/pr20701.c
index 2f914589e32..496c4256733 100644
--- a/gcc/testsuite/gcc.dg/tree-ssa/pr20701.c
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr20701.c
@@ -1,5 +1,5 @@
 /* { dg-do compile } */
-/* { dg-options "-O2 -fdump-tree-vrp1 -fno-early-inlining -fdelete-null-pointer-checks" } */
+/* { dg-options "-O2 -fdump-tree-vrp1 -fno-early-inlining -fdelete-null-pointer-checks -fdisable-tree-thread1" } */
 
 typedef struct {
   int code;
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr20702.c b/gcc/testsuite/gcc.dg/tree-ssa/pr20702.c
index c896857748c..81129674d8a 100644
--- a/gcc/testsuite/gcc.dg/tree-ssa/pr20702.c
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr20702.c
@@ -4,7 +4,7 @@
    immediate successors of the basic block.  */
 
 /* { dg-do compile } */
-/* { dg-options "-O2 -fno-tree-dominator-opts -fdisable-tree-evrp -fdump-tree-vrp1-details -fdelete-null-pointer-checks" } */
+/* { dg-options "-O2 -fno-thread-jumps -fdisable-tree-evrp -fdump-tree-vrp1-details -fdelete-null-pointer-checks" } */
 
 extern void bar (int);
 
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr21086.c b/gcc/testsuite/gcc.dg/tree-ssa/pr21086.c
index aadd53e2237..9b93d39d4e4 100644
--- a/gcc/testsuite/gcc.dg/tree-ssa/pr21086.c
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr21086.c
@@ -1,5 +1,5 @@
 /* { dg-do compile } */
-/* { dg-options "-O2 -fdisable-tree-evrp -fdump-tree-vrp1 -fdump-tree-dce2 -fdelete-null-pointer-checks" } */
+/* { dg-options "-O2 -fno-thread-jumps -fdisable-tree-evrp -fdump-tree-vrp1 -fdump-tree-dce2 -fdelete-null-pointer-checks" } */
 
 int
 foo (int *p)
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr25382.c b/gcc/testsuite/gcc.dg/tree-ssa/pr25382.c
index d74765551c2..8634c0a7895 100644
--- a/gcc/testsuite/gcc.dg/tree-ssa/pr25382.c
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr25382.c
@@ -3,7 +3,7 @@
    Check that VRP now gets ranges from BIT_AND_EXPRs.  */
 
 /* { dg-do compile } */
-/* { dg-options "-O2 -fno-tree-ccp -fdisable-tree-evrp -fdump-tree-vrp1" } */
+/* { dg-options "-O2 -fno-thread-jumps -fno-tree-ccp -fdisable-tree-evrp -fdump-tree-vrp1" } */
 
 int
 foo (int a)
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr58480.c b/gcc/testsuite/gcc.dg/tree-ssa/pr58480.c
index 42898e72d4e..f11623b7c6b 100644
--- a/gcc/testsuite/gcc.dg/tree-ssa/pr58480.c
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr58480.c
@@ -1,5 +1,5 @@
 /* { dg-do compile { target { ! keeps_null_pointer_checks } } } */
-/* { dg-options "-O2 -fdisable-tree-evrp -fdump-tree-vrp1 -fdelete-null-pointer-checks" } */
+/* { dg-options "-O2 -fno-thread-jumps -fdisable-tree-evrp -fdump-tree-vrp1 -fdelete-null-pointer-checks" } */
 
 extern void eliminate (void);
 extern void* f1 (void *a, void *b) __attribute__((nonnull));
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/ssa-dom-thread-4.c b/gcc/testsuite/gcc.dg/tree-ssa/ssa-dom-thread-4.c
deleted file mode 100644
index 9cd463571c4..00000000000
--- a/gcc/testsuite/gcc.dg/tree-ssa/ssa-dom-thread-4.c
+++ /dev/null
@@ -1,60 +0,0 @@
-/* { dg-do compile } */ 
-/* { dg-options "-O2 -fdump-tree-vrp-thread2-details -fdump-tree-dom2-details -std=gnu89 --param logical-op-non-short-circuit=1" } */
-struct bitmap_head_def;
-typedef struct bitmap_head_def *bitmap;
-typedef const struct bitmap_head_def *const_bitmap;
-typedef unsigned long BITMAP_WORD;
-typedef struct bitmap_element_def
-{
-  struct bitmap_element_def *next;
-  unsigned int indx;
-} bitmap_element;
-
-
-
-
-
-
-
-
-
-unsigned char
-bitmap_ior_and_compl (bitmap dst, const_bitmap a, const_bitmap b,
-		      const_bitmap kill)
-{
-  unsigned char changed = 0;
-
-  bitmap_element *dst_elt;
-  const bitmap_element *a_elt, *b_elt, *kill_elt, *dst_prev;
-
-  while (a_elt || b_elt)
-    {
-      unsigned char new_element = 0;
-
-      if (b_elt)
-	while (kill_elt && kill_elt->indx < b_elt->indx)
-	  kill_elt = kill_elt->next;
-
-      if (b_elt && kill_elt && kill_elt->indx == b_elt->indx
-	  && (!a_elt || a_elt->indx >= b_elt->indx))
-	{
-	  bitmap_element tmp_elt;
-	  unsigned ix;
-
-	  BITMAP_WORD ior = 0;
-
-	      changed = bitmap_elt_ior (dst, dst_elt, dst_prev,
-					a_elt, &tmp_elt, changed);
-
-	}
-
-    }
-
-
-  return changed;
-}
-/* We used to catch 3 jump threads in vrp-thread1, but they all
-   rotated the loop, so they were disallowed.  This in turn created
-   other opportunities for the other threaders which result in the the
-   post-loop threader (vrp-thread2) catching more.  */
-/* { dg-final { scan-tree-dump-times "Registering jump thread" 5 "vrp-thread2" } } */
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/ssa-dom-thread-7.c b/gcc/testsuite/gcc.dg/tree-ssa/ssa-dom-thread-7.c
deleted file mode 100644
index 1da00a691c8..00000000000
--- a/gcc/testsuite/gcc.dg/tree-ssa/ssa-dom-thread-7.c
+++ /dev/null
@@ -1,134 +0,0 @@
-/* { dg-do compile } */
-/* { dg-options "-O2 -fdump-tree-thread1-stats -fdump-tree-thread2-stats -fdump-tree-dom2-stats -fdump-tree-thread3-stats -fdump-tree-dom3-stats -fdump-tree-vrp2-stats -fno-guess-branch-probability" } */
-
-/* { dg-final { scan-tree-dump "Jumps threaded: 12"  "thread3" } } */
-/* { dg-final { scan-tree-dump-not "Jumps threaded"  "dom2" } } */
-
-/* aarch64 has the highest CASE_VALUES_THRESHOLD in GCC.  It's high enough
-   to change decisions in switch expansion which in turn can expose new
-   jump threading opportunities.  Skip the later tests on aarch64.  */
-/* { dg-final { scan-tree-dump-not "Jumps threaded"  "dom3" { target { ! aarch64*-*-* } } } } */
-/* { dg-final { scan-tree-dump-not "Jumps threaded"  "vrp-thread2" { target { ! aarch64*-*-* } } } } */
-
-enum STATE {
-  S0=0,
-  SI,
-  S1,
-  S2,
-  S3,
-  S4,
-  S5,
-  S6
-};
-
-int bar (enum STATE s);
-
-enum STATE foo (unsigned char **y, unsigned *c)
-{
-  unsigned char *x = *y;
-  unsigned char n;
-  enum STATE s = S0;
-
-  for( ; *x && s != SI; x++ )
-    {
-      n = *x;
-      if (n == 'x')
-	{
-	  x++;
-	  break;
-	}
-      switch(s)
-	{
-	case S0:
-	  if(bar(n))
-	    s = S3;
-	  else if( n == 'a' || n == 'b' )
-	    s = S1;
-	  else if( n == 'c' )
-	    s = S4;
-	  else
-	    {
-	      s = SI;
-	      c[SI]++;
-	    }
-	  c[S0]++;
-	  break;
-	case S1:
-	  if(bar(n))
-	    {
-	      s = S3;
-	      c[S1]++;
-	    }
-	  else if( n == 'c' )
-	    {
-	      s = S4;
-	      c[S1]++;
-	    }
-	  else
-	    {
-	      s = SI;
-	      c[S1]++;
-	    }
-	  break;
-	case S3:
-	  if( n == 'c' )
-	    {
-	      s = S4;
-	      c[S3]++;
-	    }
-	  else if(!bar(n))
-	    {
-	      s = SI;
-	      c[S3]++;
-	    }
-	  break;
-	case S4:
-	  if( n == 'E' || n == 'e' )
-	    {
-	      s = S2;
-	      c[S4]++;
-	    }
-	  else if(!bar(n))
-	    {
-	      s = SI;
-	      c[S4]++;
-	    }
-	  break;
-	case S2:
-	  if( n == 'a' || n == 'b' )
-	    {
-	      s = S5;
-	      c[S2]++;
-	    }
-	  else
-	    {
-	      s = SI;
-	      c[S2]++;
-	    }
-	  break;
-	case S5:
-	  if(bar(n))
-	    {
-	      s = S6;
-	      c[S5]++;
-	    }
-	  else
-	    {
-	      s = SI;
-	      c[S5]++;
-	    }
-	  break;
-	case S6:
-	  if(!bar(n))
-	    {
-	      s = SI;
-	      c[SI]++;
-	    }
-	  break;
-	default:
-	  break;
-	}
-    }
-  *y=x;
-  return s;
-}
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/ssa-thread-11.c b/gcc/testsuite/gcc.dg/tree-ssa/ssa-thread-11.c
deleted file mode 100644
index 672a54e07db..00000000000
--- a/gcc/testsuite/gcc.dg/tree-ssa/ssa-thread-11.c
+++ /dev/null
@@ -1,50 +0,0 @@
-/* { dg-do compile } */
-/* { dg-options "-O2 -fdump-tree-vrp2-details --param logical-op-non-short-circuit=1" } */
-/* { dg-additional-options "-fdisable-tree-ethread -fdisable-tree-thread1 -fdisable-tree-thread2" } */
-/* { dg-final { scan-tree-dump-not "IRREDUCIBLE_LOOP" "vrp2" } } */
-
-void abort (void);
-typedef struct bitmap_head_def *bitmap;
-typedef const struct bitmap_head_def *const_bitmap;
-typedef struct bitmap_obstack
-{
-  struct bitmap_obstack *next;
-  unsigned int indx;
-}
-bitmap_element;
-typedef struct bitmap_head_def
-{
-  bitmap_element *first;
-}
-bitmap_head;
-static __inline__ unsigned char
-bitmap_elt_ior (bitmap dst, bitmap_element * dst_elt,
-		bitmap_element * dst_prev, const bitmap_element * a_elt,
-		const bitmap_element * b_elt)
-{
-  ((void) (!(a_elt || b_elt) ? abort (), 0 : 0));
-}
-
-unsigned char
-bitmap_ior_and_compl (bitmap dst, const_bitmap a, const_bitmap b,
-		      const_bitmap kill)
-{
-  bitmap_element *dst_elt = dst->first;
-  const bitmap_element *a_elt = a->first;
-  const bitmap_element *b_elt = b->first;
-  const bitmap_element *kill_elt = kill->first;
-  bitmap_element *dst_prev = ((void *) 0);
-  while (a_elt || b_elt)
-    {
-      if (b_elt && kill_elt && kill_elt->indx == b_elt->indx
-	  && (!a_elt || a_elt->indx >= b_elt->indx));
-      else
-	{
-	  bitmap_elt_ior (dst, dst_elt, dst_prev, a_elt, b_elt);
-	  if (a_elt && b_elt && a_elt->indx == b_elt->indx)
-	    ;
-	  else if (a_elt && (!b_elt || a_elt->indx <= b_elt->indx))
-	    a_elt = a_elt->next;
-	}
-    }
-}
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/ssa-thread-backedge.c b/gcc/testsuite/gcc.dg/tree-ssa/ssa-thread-backedge.c
new file mode 100644
index 00000000000..890a0ee10ec
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/ssa-thread-backedge.c
@@ -0,0 +1,32 @@
+// { dg-do compile }
+// { dg-options "-O2 -fdisable-tree-ethread -fdisable-tree-thread1 -fdisable-tree-thread2 -fno-tree-dominator-opts -fdump-tree-thread3-details" }
+
+// Test that we can thread jumps across the backedge of a loop through
+// the switch statement to a particular case.
+//
+// Just in case, we disable all the jump threaders before loop
+// optimizations to make sure we get a clean stab at this.
+
+int foo (unsigned int x, int s)
+{
+  while (s != 999)
+    {
+      switch (s)
+	{
+	case 0:
+	  if (x)
+	    s = 1;
+	  break;
+	case 1:
+	  if (x)
+	    s = 999;
+	  break;
+	default:
+	  break;
+	}
+      x++;
+    }
+  return s;
+}
+
+// { dg-final { scan-tree-dump "Registering jump thread:.*normal \\(back\\)" "thread3" } }
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/ssa-vrp-thread-1.c b/gcc/testsuite/gcc.dg/tree-ssa/ssa-vrp-thread-1.c
index 86d07ef9bdb..f3ca140bd26 100644
--- a/gcc/testsuite/gcc.dg/tree-ssa/ssa-vrp-thread-1.c
+++ b/gcc/testsuite/gcc.dg/tree-ssa/ssa-vrp-thread-1.c
@@ -1,5 +1,5 @@
 /* { dg-do compile } */
-/* { dg-options "-O2 -fdump-tree-vrp-thread1-details -fdelete-null-pointer-checks" } */
+/* { dg-options "-O2 -fdump-tree-thread1-details -fdelete-null-pointer-checks" } */
 /* { dg-skip-if "" keeps_null_pointer_checks } */
 
 void oof (void);
@@ -29,5 +29,5 @@ build_omp_regions_1 (basic_block bb, struct omp_region *parent,
 
 /* ARM Cortex-M defined LOGICAL_OP_NON_SHORT_CIRCUIT to false,
    so skip below test.  */
-/* { dg-final { scan-tree-dump-times "Threaded" 1 "vrp-thread1" { target { ! arm_cortex_m } } } } */
+/* { dg-final { scan-tree-dump-times "Registering jump thread" 1 "thread1" { target { ! arm_cortex_m } } } } */
 
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/vrp08.c b/gcc/testsuite/gcc.dg/tree-ssa/vrp08.c
index c2da30b4b68..2c6742b76c7 100644
--- a/gcc/testsuite/gcc.dg/tree-ssa/vrp08.c
+++ b/gcc/testsuite/gcc.dg/tree-ssa/vrp08.c
@@ -1,5 +1,5 @@
 /* { dg-do compile } */
-/* { dg-options "-O2 -fno-tree-fre -fdisable-tree-evrp -fdump-tree-vrp1-details -fdelete-null-pointer-checks" } */
+/* { dg-options "-O2 -fno-tree-fre -fdisable-tree-evrp -fdump-tree-vrp1-details -fdisable-tree-thread1 -fdelete-null-pointer-checks" } */
 
 /* Compile with -fno-tree-fre -O2 to prevent CSEing *p.  */
 int
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/vrp55.c b/gcc/testsuite/gcc.dg/tree-ssa/vrp55.c
index a478a6981ac..0ef57d935e4 100644
--- a/gcc/testsuite/gcc.dg/tree-ssa/vrp55.c
+++ b/gcc/testsuite/gcc.dg/tree-ssa/vrp55.c
@@ -1,5 +1,5 @@
 /* { dg-do compile } */
-/* { dg-options "-O2 -fdump-tree-vrp-thread1-blocks-vops-details -fdelete-null-pointer-checks" } */
+/* { dg-options "-O2 -fdump-tree-ethread-details -fdelete-null-pointer-checks" } */
 
 void arf (void);
 
@@ -12,6 +12,6 @@ fu (char *p, int x)
     arf ();
 }
 
-/* { dg-final { scan-tree-dump-times "Threaded jump" 1 "vrp-thread1" { target { ! keeps_null_pointer_checks } } } } */
-/* { dg-final { scan-tree-dump-times "Threaded jump" 0 "vrp-thread1" { target {   keeps_null_pointer_checks } } } } */
+/* { dg-final { scan-tree-dump-times "Registering jump thread" 1 "ethread" { target { ! keeps_null_pointer_checks } } } } */
+/* { dg-final { scan-tree-dump-times "Registering jump thread" 0 "ethread" { target {   keeps_null_pointer_checks } } } } */
 
diff --git a/gcc/testsuite/gcc.dg/uninit-pr89230-1.c b/gcc/testsuite/gcc.dg/uninit-pr89230-1.c
index 1c07c4f6d78..dfc87a5b1a0 100644
--- a/gcc/testsuite/gcc.dg/uninit-pr89230-1.c
+++ b/gcc/testsuite/gcc.dg/uninit-pr89230-1.c
@@ -8,7 +8,8 @@ struct S { int i, j; };
 
 int g (void)
 {
-  struct S *p = f (), *q;
+  struct S *p = f ();
+  struct S *q; // { dg-bogus "may be used uninitialized" "uninitialized" { xfail *-*-* } }
 
   if (p->i || !(q = f ()) || p->j != q->i)
    {
diff --git a/gcc/tree-ssa-threadbackward.c b/gcc/tree-ssa-threadbackward.c
index 38913b06717..1301d52618b 100644
--- a/gcc/tree-ssa-threadbackward.c
+++ b/gcc/tree-ssa-threadbackward.c
@@ -378,8 +378,8 @@ back_threader::find_paths_to_names (basic_block bb, bitmap interesting)
       return false;
     }
 
-  // Try to resolve the path with nothing but ranger knowledge.
-  if (m_resolve && m_path.length () > 1 && maybe_register_path ())
+  // Try to resolve the path without looking back.
+  if (m_path.length () > 1 && maybe_register_path ())
     {
       m_path.pop ();
       m_visited_bbs.remove (bb);
diff --git a/gcc/tree-ssa-threadupdate.c b/gcc/tree-ssa-threadupdate.c
index 8e6f043bb44..8aac733ac25 100644
--- a/gcc/tree-ssa-threadupdate.c
+++ b/gcc/tree-ssa-threadupdate.c
@@ -253,6 +253,9 @@ dump_jump_thread_path (FILE *dump_file,
 	default:
 	  gcc_unreachable ();
 	}
+
+      if ((path[i]->e->flags & EDGE_DFS_BACK) != 0)
+	fprintf (dump_file, " (back)");
     }
   fprintf (dump_file, "; \n");
 }
-- 
2.31.1