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Fix PR64878: do not jump thread across two loop iterations


Hi,

The attached patch stops the recursion in the detection of FSM jump-threads at
loop phi nodes after having visited a loop phi node.  This avoids jump-threading
two iterations forward that were possible due to a flip-flop operation that
exchange the value of the switch control variable as illustrated in the
testcase:

do {
  c = read_from_memory;
  switch (a) {
  case 0:
    if (c == ' ')
     [...]
    else
      a = b;   // flip-flop
    break;
  case 1:
    a = 0;
    b = 15; // this will jump-thread to 15
    break;

  case 15:
  [...]
  }
} while (...);

The patch has passed bootstrap and regression testing on x86_64-linux.
Ok to commit?

Thanks,
Sebastian
>From 59c486720749fc3d5feac2a5364d52eac60ba2d0 Mon Sep 17 00:00:00 2001
From: Sebastian Pop <s.pop@samsung.com>
Date: Wed, 4 Feb 2015 11:17:54 -0600
Subject: [PATCH] PR 64878: do not jump thread across more than one back-edge

2015-02-04  Sebastian Pop  <s.pop@samsung.com>
	    Brian Rzycki  <b.rzycki@samsung.com>

	PR tree-optimization/64878
	* tree-ssa-threadedge.c: Include tree-ssa-loop.h.
	(fsm_find_control_statement_thread_paths): Add parameter seen_loop_phi.
	Stop recursion at loop phi nodes after having visited a loop phi node.

	* testsuite/gcc.dg/tree-ssa/ssa-dom-thread-8.c: New.
---
 gcc/testsuite/gcc.dg/tree-ssa/ssa-dom-thread-8.c | 440 +++++++++++++++++++++++
 gcc/tree-ssa-threadedge.c                        |  20 +-
 2 files changed, 457 insertions(+), 3 deletions(-)
 create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/ssa-dom-thread-8.c

diff --git a/gcc/testsuite/gcc.dg/tree-ssa/ssa-dom-thread-8.c b/gcc/testsuite/gcc.dg/tree-ssa/ssa-dom-thread-8.c
new file mode 100644
index 0000000..9be75aa
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/ssa-dom-thread-8.c
@@ -0,0 +1,440 @@
+/* PR 64878 */
+/* { dg-options "-O2" } */
+/* { dg-do run } */
+
+struct A { int a1; };
+struct B { char *b1; int b2; int b3; };
+struct C { char *c1; int c2; struct B *c3; };
+extern struct A *f1 (char *s);
+static struct A *f2 (struct C *x);
+__attribute__ ((noinline, noclone)) int f3 (struct A *x, struct A *z) { asm volatile ("" : : "g" (x), "g" (z) : "memory"); return 0; }
+__attribute__ ((noinline, noclone)) void f4 (struct A *x, char *y, struct A *z) { asm volatile ("" : : "g" (x), "g" (z), "g" (y) : "memory"); }
+__attribute__ ((noinline, noclone)) struct B *f5 (void) { static char b[32]; static struct B f3 = { b, 0, 32 }; return &f3; }
+__attribute__ ((noinline, noclone)) int f6 (struct B *p, char *w, int z) { asm volatile ("" : : "g" (p), "g" (w), "g" (z) : "memory"); return 0; }
+__attribute__ ((noinline, noclone)) void f7 (struct B *p) { asm volatile ("" : : "g" (p) : "memory"); }
+__attribute__ ((noinline, noclone)) void f8 (struct B *p) { asm volatile ("" : : "g" (p) : "memory"); }
+__attribute__ ((noinline, noclone)) void f9 (struct A *x) { asm volatile ("" : : "g" (x) : "memory"); }
+__attribute__ ((noinline, noclone)) struct A *f10 (void) { static struct A j; asm volatile ("" : :  : "memory"); return &j; }
+__attribute__ ((noinline, noclone)) struct A *f11 (void) { static struct A j; asm volatile ("" : :  : "memory"); return &j; }
+__attribute__ ((noinline, noclone)) struct A *f12 (int b) { static struct A j; asm volatile ("" : : "g" (b) : "memory"); return &j; }
+__attribute__ ((noinline, noclone)) struct A *f13 (int i) { static struct A j; asm volatile ("" : : "g" (i) : "memory"); return &j; }
+__attribute__ ((noinline, noclone)) struct A *f14 (double d) { static struct A j; asm volatile ("" : : "g" (&d) : "memory"); return &j; }
+__attribute__ ((noinline, noclone)) struct A *f15 (char *s) { static struct A j; asm volatile ("" : : "g" (s) : "memory"); return &j; }
+char *t = "0123456789abcdef";
+char *u = "0123456789.+-e";
+
+__attribute__ ((noinline, noclone)) struct A *
+f1 (char *s)
+{
+  struct C f;
+  struct A *o;
+  f.c1 = s;
+  f.c2 = 0;
+  f.c3 = f5 ();
+  o = f2 (&f);
+  f8 (f.c3);
+  return o;
+}
+
+static struct A *
+f2 (struct C *x)
+{
+  int a, b, e = 0;
+  struct A *f = 0, *o;
+  char *g = 0;
+  char h = '\0';
+  int i = 0, j = 0;
+  a = 0;
+  b = 1;
+  char c;
+  do
+    {
+      c = x->c1[x->c2];
+      switch (a)
+	{
+	case 0:
+	  if (c == ' ')
+	    x->c2++;
+	  else if (c == '/')
+	    {
+	      a = 4;
+	      j = x->c2++;
+	    }
+	  else
+	    a = b;
+	  break;
+	case 1:
+	  switch (c)
+	    {
+	    case '{':
+	      a = 0;
+	      b = 15;
+	      f = f10 ();
+	      x->c2++;
+	      break;
+	    case '[':
+	      a = 0;
+	      b = 13;
+	      f = f11 ();
+	      x->c2++;
+	      break;
+	    case 'N':
+	    case 'n':
+	      a = 3;
+	      j = x->c2++;
+	      break;
+	    case '"':
+	    case '\'':
+	      h = c;
+	      f7 (x->c3);
+	      a = 8;
+	      j = ++x->c2;
+	      break;
+	    case 'T':
+	    case 't':
+	    case 'F':
+	    case 'f':
+	      a = 11;
+	      j = x->c2++;
+	      break;
+	    case '0' ... '9':
+	    case '-':
+	      i = 0;
+	      a = 12;
+	      j = x->c2++;
+	      break;
+	    default:
+	      e = 1;
+	      goto out;
+	    }
+	  break;
+	case 2:
+	  goto out;
+	case 3:
+	  if (__builtin_strncmp ("null", x->c1 + j, x->c2 - j))
+	    {
+	      e = 2;
+	      goto out;
+	    }
+	  if (x->c2 - j == 4)
+	    {
+	      f = 0;
+	      b = 2;
+	      a = 0;
+	    }
+	  else
+	    x->c2++;
+	  break;
+	case 4:
+	  if (c == '*')
+	    a = 5;
+	  else if (c == '/')
+	    a = 6;
+	  else
+	    {
+	      e = 8;
+	      goto out;
+	    }
+	  x->c2++;
+	  break;
+	case 5:
+	  if (c == '*')
+	    a = 7;
+	  x->c2++;
+	  break;
+	case 6:
+	  if (c == '\n')
+	    a = 0;
+	  x->c2++;
+	  break;
+	case 7:
+	  if (c == '/')
+	    a = 0;
+	  else
+	    a = 5;
+	  x->c2++;
+	  break;
+	case 8:
+	  if (c == h)
+	    {
+	      f6 (x->c3, x->c1 + j, x->c2 - j);
+	      f = f15 (x->c3->b1);
+	      b = 2;
+	      a = 0;
+	    }
+	  else if (c == '\\')
+	    {
+	      b = 8;
+	      a = 9;
+	    }
+	  x->c2++;
+	  break;
+	case 9:
+	  switch (c)
+	    {
+	    case '"':
+	    case '\\':
+	      f6 (x->c3, x->c1 + j, x->c2 - j - 1);
+	      j = x->c2++;
+	      a = b;
+	      break;
+	    case 'b':
+	    case 'n':
+	    case 'r':
+	    case 't':
+	      f6 (x->c3, x->c1 + j, x->c2 - j - 1);
+	      if (c == 'b')
+		f6 (x->c3, "\b", 1);
+	      else if (c == 'n')
+		f6 (x->c3, "\n", 1);
+	      else if (c == 'r')
+		f6 (x->c3, "\r", 1);
+	      else if (c == 't')
+		f6 (x->c3, "\t", 1);
+	      j = ++x->c2;
+	      a = b;
+	      break;
+	    case 'u':
+	      f6 (x->c3, x->c1 + j, x->c2 - j - 1);
+	      j = ++x->c2;
+	      a = 10;
+	      break;
+	    default:
+	      e = 7;
+	      goto out;
+	    }
+	  break;
+	case 10:
+	  if (__builtin_strchr (t, c))
+	    {
+	      x->c2++;
+	      if (x->c2 - j == 4)
+		{
+		  unsigned char w[3];
+		  unsigned int s =
+		    (((x->c1[j] <= '9') ? x->c1[j] - '0' : (x->c1[j] & 7) + 9) << 12)
+		    + (((x->c1[j + 1] <= '9') ? x->c1[j + 1] - '0' : (x->c1[j + 1] & 7) + 9) << 8)
+		    + (((x->c1[j + 2] <= '9') ? x->c1[j + 2] - '0' : (x->c1[j + 2] & 7) + 9) << 4)
+		    + ((x->c1[j + 3] <= '9') ? x->c1[j + 3] - '0' : (x->c1[j + 3] & 7) + 9);
+		  if (s < 0x80)
+		    {
+		      w[0] = s;
+		      f6 (x->c3, (char *) w, 1);
+		    }
+		  else if (s < 0x800)
+		    {
+		      w[0] = 0xc0 | (s >> 6);
+		      w[1] = 0x80 | (s & 0x3f);
+		      f6 (x->c3, (char *) w, 2);
+		    }
+		  else
+		    {
+		      w[0] = 0x0 | (s >> 12);
+		      w[1] = 0x80 | ((s >> 6) & 0x3f);
+		      w[2] = 0x80 | (s & 0x3f);
+		      f6 (x->c3, (char *) w, 3);
+		    }
+		  j = x->c2;
+		  a = b;
+		}
+	    }
+	  else
+	    {
+	      e = 7;
+	      goto out;
+	    }
+	  break;
+	case 11:
+	  if (__builtin_strncmp ("true", x->c1 + j, x->c2 - j) == 0)
+	    {
+	      if (x->c2 - j == 4)
+		{
+		  f = f12 (1);
+		  b = 2;
+		  a = 0;
+		}
+	      else
+		x->c2++;
+	    }
+	  else if (__builtin_strncmp ("false", x->c1 + j, x->c2 - j) == 0)
+	    {
+	      if (x->c2 - j == 5)
+		{
+		  f = f12 (0);
+		  b = 2;
+		  a = 0;
+		}
+	      else
+		x->c2++;
+	    }
+	  else
+	    {
+	      e = 3;
+	      goto out;
+	    }
+	  break;
+	case 12:
+	  if (!c || !__builtin_strchr (u, c))
+	    {
+	      if (!i)
+		f = f13 (0);
+	      else
+		f = f14 (0.0);
+	      b = 2;
+	      a = 0;
+	    }
+	  else
+	    {
+	      if (c == '.' || c == 'e')
+		i = 1;
+	      x->c2++;
+	    }
+	  break;
+	case 13:
+	  if (c == ']')
+	    {
+	      x->c2++;
+	      b = 2;
+	      a = 0;
+	    }
+	  else
+	    {
+	      o = f2 (x);
+	      if (((unsigned long) o > (unsigned long) -4000L))
+		{
+		  e = 5;
+		  goto out;
+		}
+	      f3 (f, o);
+	      b = 14;
+	      a = 0;
+	    }
+	  break;
+	case 14:
+	  if (c == ']')
+	    {
+	      x->c2++;
+	      b = 2;
+	      a = 0;
+	    }
+	  else if (c == ',')
+	    {
+	      x->c2++;
+	      b = 13;
+	      a = 0;
+	    }
+	  else
+	    {
+	      f9 (f);
+	      e = 5;
+	      goto out;
+	    }
+	  break;
+	case 15:
+	  a = 16;
+	  j = x->c2;
+	  break;
+	case 16:
+	  if (c == '}')
+	    {
+	      x->c2++;
+	      b = 2;
+	      a = 0;
+	    }
+	  else if (c == '"' || c == '\'')
+	    {
+	      h = c;
+	      f7 (x->c3);
+	      a = 17;
+	      j = ++x->c2;
+	    }
+	  else
+	    {
+	      e = 6;
+	      goto out;
+	    }
+	  break;
+	case 17:
+	  if (c == h)
+	    {
+	      f6 (x->c3, x->c1 + j, x->c2 - j);
+	      g = __builtin_strdup (x->c3->b1);
+	      b = 18;
+	      a = 0;
+	    }
+	  else if (c == '\\')
+	    {
+	      b = 17;
+	      a = 9;
+	    }
+	  x->c2++;
+	  break;
+	case 18:
+	  if (c == ':')
+	    {
+	      x->c2++;
+	      b = 19;
+	      a = 0;
+	    }
+	  else
+	    {
+	      e = -6;
+	      goto out;
+	    }
+	  break;
+	case 19:
+	  o = f2 (x);
+	  if (((unsigned long) o > (unsigned long) -4000L))
+	    {
+	      e = 6;
+	      goto out;
+	    }
+	  f4 (f, g, o);
+	  __builtin_free (g);
+	  g = 0;
+	  b = 20;
+	  a = 0;
+	  break;
+	case 20:
+	  if (c == '}')
+	    {
+	      x->c2++;
+	      b = 2;
+	      a = 0;
+	    }
+	  else if (c == ',')
+	    {
+	      x->c2++;
+	      b = 15;
+	      a = 0;
+	    }
+	  else
+	    {
+	      e = 6;
+	      goto out;
+	    }
+	  break;
+	}
+    }
+  while (c);
+  if (a != 2 && b != 2)
+    e = 9;
+out:
+  __builtin_free (g);
+  if (e == 0)
+    return f;
+  f9 (f);
+  return 0;
+}
+
+int
+main ()
+{
+  asm volatile ("" : : : "memory");
+  struct A *r = f1 ("{ \"id\": null, \"blahah\": \"foobarbazbar\", \"barbar\": { \"barbarbarba\":"
+		    "\"abcdefgh\", \"ijklmnopqr\": \"stuvwxyzabcdefghijklmnopqrstuv\", \"xyzxyz\":"
+		    " [ \"1\" ] } }");
+  if (!r)
+    __builtin_abort ();
+  return 0;
+}
diff --git a/gcc/tree-ssa-threadedge.c b/gcc/tree-ssa-threadedge.c
index 9e10e44..b2e7764 100644
--- a/gcc/tree-ssa-threadedge.c
+++ b/gcc/tree-ssa-threadedge.c
@@ -61,6 +61,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "langhooks.h"
 #include "params.h"
 #include "tree-ssa-threadedge.h"
+#include "tree-ssa-loop.h"
 #include "builtins.h"
 #include "cfg.h"
 #include "cfganal.h"
@@ -1006,7 +1007,8 @@ static int max_threaded_paths;
 static void
 fsm_find_control_statement_thread_paths (tree expr,
 					 hash_set<gimple> *visited_phis,
-					 vec<basic_block, va_gc> *&path)
+					 vec<basic_block, va_gc> *&path,
+					 bool seen_loop_phi)
 {
   tree var = SSA_NAME_VAR (expr);
   gimple def_stmt = SSA_NAME_DEF_STMT (expr);
@@ -1030,6 +1032,15 @@ fsm_find_control_statement_thread_paths (tree expr,
   int next_path_length = 0;
   basic_block last_bb_in_path = path->last ();
 
+  if (loop_containing_stmt (phi)->header == gimple_bb (phi))
+    {
+      /* PR64878: do not take more than a loop phi node: it may be a flip-flop
+	 operation across two latch edges.  */
+      if (seen_loop_phi)
+	return;
+      seen_loop_phi = true;
+    }
+
   /* Following the chain of SSA_NAME definitions, we jumped from a definition in
      LAST_BB_IN_PATH to a definition in VAR_BB.  When these basic blocks are
      different, append to PATH the blocks from LAST_BB_IN_PATH to VAR_BB.  */
@@ -1090,7 +1101,9 @@ fsm_find_control_statement_thread_paths (tree expr,
 	{
 	  vec_safe_push (path, bbi);
 	  /* Recursively follow SSA_NAMEs looking for a constant definition.  */
-	  fsm_find_control_statement_thread_paths (arg, visited_phis, path);
+	  fsm_find_control_statement_thread_paths (arg, visited_phis, path,
+						   seen_loop_phi);
+
 	  path->pop ();
 	  continue;
 	}
@@ -1357,7 +1370,8 @@ thread_through_normal_block (edge e,
       hash_set<gimple> *visited_phis = new hash_set<gimple>;
 
       max_threaded_paths = PARAM_VALUE (PARAM_MAX_FSM_THREAD_PATHS);
-      fsm_find_control_statement_thread_paths (cond, visited_phis, bb_path);
+      fsm_find_control_statement_thread_paths (cond, visited_phis, bb_path,
+					       false);
 
       delete visited_phis;
       vec_free (bb_path);
-- 
1.9.1


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