Hi,
this patches fixes profile updating in the ifcombine.  This is not hard to do
and ifcombine is #2 profile update offender out of tree passes (#1 is the
vectorizer).

I think this counts as a regression, becuase one can trigger arbitrarily
bad profile after ifconversion and defnitly construct a testcase where this
will cause us optimize for size where we optimized for speed previously.

Bootstrapped/regtested x86_64-linux. Will commit it tomorrow (after testers
pick up the threading fix) unless there are complains.

        * gcc.dg/tree-ssa/ssa-ifcombine-1.c: Check for no profile mismatches.
        * gcc.dg/tree-ssa/ssa-ifcombine-2.c: Check for no profile mismatches.
        * gcc.dg/tree-ssa/ssa-ifcombine-3.c: Check for no profile mismatches.
        * gcc.dg/tree-ssa/ssa-ifcombine-4.c: Check for no profile mismatches.
        * gcc.dg/tree-ssa/ssa-ifcombine-5.c: Check for no profile mismatches.
        * gcc.dg/tree-ssa/ssa-ifcombine-6.c: Check for no profile mismatches.
        * gcc.dg/tree-ssa/ssa-ifcombine-7.c: Check for no profile mismatches.
        * gcc.dg/tree-ssa/ssa-ifcombine-8.c: Check for no profile mismatches.
        * gcc.dg/tree-ssa/ssa-ifcombine-9.c: Check for no profile mismatches.
        * gcc.dg/tree-ssa/ssa-ifcombine-10.c: Check for no profile mismatches.
        * gcc.dg/tree-ssa/ssa-ifcombine-11.c: Check for no profile mismatches.
        * gcc.dg/tree-ssa/ssa-ifcombine-12.c: Check for no profile mismatches.
        * gcc.dg/tree-ssa/ssa-ifcombine-13.c: Check for no profile mismatches.

        * tree-ssa-ifcombine.c (update_profile_after_ifcombine): New function.
        (ifcombine_ifandif): Use it.

Index: testsuite/gcc.dg/tree-ssa/ssa-ifcombine-1.c
===================================================================
--- testsuite/gcc.dg/tree-ssa/ssa-ifcombine-1.c (revision 245134)
+++ testsuite/gcc.dg/tree-ssa/ssa-ifcombine-1.c (working copy)
@@ -1,5 +1,5 @@
 /* { dg-do compile } */
-/* { dg-options "-O -fdump-tree-optimized" } */
+/* { dg-options "-O -fdump-tree-optimized-details-blocks" } */
 
 /* Testcase for PR31657.  */
 
@@ -14,3 +14,4 @@ int foo (int x, int a, int b)
 }
 
 /* { dg-final { scan-tree-dump "\\|" "optimized" } } */
+/* { dg-final { scan-tree-dump-not "Invalid sum" "optimized" } } */
Index: testsuite/gcc.dg/tree-ssa/ssa-ifcombine-10.c
===================================================================
--- testsuite/gcc.dg/tree-ssa/ssa-ifcombine-10.c        (revision 245134)
+++ testsuite/gcc.dg/tree-ssa/ssa-ifcombine-10.c        (working copy)
@@ -1,5 +1,5 @@
 /* { dg-do compile } */
-/* { dg-options "-O2 -fdump-tree-optimized" } */
+/* { dg-options "-O2 -fdump-tree-optimized-details-blocks" } */
 
 /* Testcase for PR31657.  */
 
@@ -17,3 +17,4 @@ int f(int x, int a, int b)
   return t;
 }
 /* { dg-final { scan-tree-dump "& 5" "optimized" } } */
+/* { dg-final { scan-tree-dump-not "Invalid sum" "optimized" } } */
Index: testsuite/gcc.dg/tree-ssa/ssa-ifcombine-11.c
===================================================================
--- testsuite/gcc.dg/tree-ssa/ssa-ifcombine-11.c        (revision 245134)
+++ testsuite/gcc.dg/tree-ssa/ssa-ifcombine-11.c        (working copy)
@@ -1,5 +1,5 @@
 /* { dg-do compile } */
-/* { dg-options "-O -fdump-tree-optimized" } */
+/* { dg-options "-O -fdump-tree-optimized-details-blocks" } */
 
 /* Testcase for PR31657.  */
 int g(void);
@@ -18,3 +18,4 @@ int f(int x, int a, int b)
 }
 
 /* { dg-final { scan-tree-dump "& 5" "optimized" } } */
+/* { dg-final { scan-tree-dump-not "Invalid sum" "optimized" } } */
Index: testsuite/gcc.dg/tree-ssa/ssa-ifcombine-12.c
===================================================================
--- testsuite/gcc.dg/tree-ssa/ssa-ifcombine-12.c        (revision 245134)
+++ testsuite/gcc.dg/tree-ssa/ssa-ifcombine-12.c        (working copy)
@@ -1,5 +1,5 @@
 /* { dg-do compile } */
-/* { dg-options "-O2 -fno-tree-vrp -fdump-tree-optimized" } */
+/* { dg-options "-O2 -fno-tree-vrp -fdump-tree-optimized-details-blocks" } */
 
 /* Testcase for PR31657.  */
 
@@ -17,3 +17,4 @@ int f(int x, int a, int b)
   return t;
 }
 /* { dg-final { scan-tree-dump "& 5" "optimized" } } */
+/* { dg-final { scan-tree-dump-not "Invalid sum" "optimized" } } */
Index: testsuite/gcc.dg/tree-ssa/ssa-ifcombine-13.c
===================================================================
--- testsuite/gcc.dg/tree-ssa/ssa-ifcombine-13.c        (revision 245134)
+++ testsuite/gcc.dg/tree-ssa/ssa-ifcombine-13.c        (working copy)
@@ -1,5 +1,5 @@
 /* { dg-do compile } */
-/* { dg-options "-O1 -fdump-tree-optimized" } */
+/* { dg-options "-O1 -fdump-tree-optimized-details-blocks" } */
 /* { dg-additional-options "-mbranch-cost=2" { target { i?86-*-* x86_64-*-* 
s390*-*-* avr*-*-* } } } */
 
 _Bool f1(_Bool a, _Bool b)
@@ -18,3 +18,4 @@ _Bool f1(_Bool a, _Bool b)
 /* For LOGICAL_OP_NON_SHORT_CIRCUIT, this should be optimized
    into return a & b;, with no ifs.  */
 /* { dg-final { scan-tree-dump-not "if" "optimized" { target { i?86-*-* 
x86_64-*-* s390*-*-* avr*-*-* } } } } */
+/* { dg-final { scan-tree-dump-not "Invalid sum" "optimized" } } */
Index: testsuite/gcc.dg/tree-ssa/ssa-ifcombine-2.c
===================================================================
--- testsuite/gcc.dg/tree-ssa/ssa-ifcombine-2.c (revision 245134)
+++ testsuite/gcc.dg/tree-ssa/ssa-ifcombine-2.c (working copy)
@@ -1,5 +1,5 @@
 /* { dg-do compile } */
-/* { dg-options "-O -fdump-tree-optimized" } */
+/* { dg-options "-O -fdump-tree-optimized-details-blocks" } */
 
 /* Testcase for PR31657.  */
 
@@ -20,3 +20,4 @@ doit:
 }
 
 /* { dg-final { scan-tree-dump "\\|" "optimized" } } */
+/* { dg-final { scan-tree-dump-not "Invalid sum" "optimized" } } */
Index: testsuite/gcc.dg/tree-ssa/ssa-ifcombine-3.c
===================================================================
--- testsuite/gcc.dg/tree-ssa/ssa-ifcombine-3.c (revision 245134)
+++ testsuite/gcc.dg/tree-ssa/ssa-ifcombine-3.c (working copy)
@@ -1,5 +1,5 @@
 /* { dg-do compile } */
-/* { dg-options "-O -fdump-tree-optimized" } */
+/* { dg-options "-O -fdump-tree-optimized-details-blocks" } */
 
 /* Testcase extracted from PR15353.  */
 
@@ -20,3 +20,4 @@ doit:
 }
 
 /* { dg-final { scan-tree-dump ">=" "optimized" } } */
+/* { dg-final { scan-tree-dump-not "Invalid sum" "optimized" } } */
Index: testsuite/gcc.dg/tree-ssa/ssa-ifcombine-4.c
===================================================================
--- testsuite/gcc.dg/tree-ssa/ssa-ifcombine-4.c (revision 245134)
+++ testsuite/gcc.dg/tree-ssa/ssa-ifcombine-4.c (working copy)
@@ -1,5 +1,5 @@
 /* { dg-do compile } */
-/* { dg-options "-O -fdump-tree-optimized" } */
+/* { dg-options "-O -fdump-tree-optimized-details-blocks" } */
 
 /* Testcase extracted from PR15353.  */
 
@@ -18,3 +18,4 @@ void foo (int x, int a)
 }
 
 /* { dg-final { scan-tree-dump "!=" "optimized" } } */
+/* { dg-final { scan-tree-dump-not "Invalid sum" "optimized" } } */
Index: testsuite/gcc.dg/tree-ssa/ssa-ifcombine-5.c
===================================================================
--- testsuite/gcc.dg/tree-ssa/ssa-ifcombine-5.c (revision 245134)
+++ testsuite/gcc.dg/tree-ssa/ssa-ifcombine-5.c (working copy)
@@ -1,5 +1,5 @@
 /* { dg-do compile } */
-/* { dg-options "-O -fdump-tree-optimized" } */
+/* { dg-options "-O -fdump-tree-optimized-details-blocks" } */
 
 /* Testcase from PR15353.  */
 
@@ -17,3 +17,4 @@ int f(int *i, int *j)
 }
 
 /* { dg-final { scan-tree-dump ">=" "optimized" } } */
+/* { dg-final { scan-tree-dump-not "Invalid sum" "optimized" } } */
Index: testsuite/gcc.dg/tree-ssa/ssa-ifcombine-6.c
===================================================================
--- testsuite/gcc.dg/tree-ssa/ssa-ifcombine-6.c (revision 245134)
+++ testsuite/gcc.dg/tree-ssa/ssa-ifcombine-6.c (working copy)
@@ -1,5 +1,5 @@
 /* { dg-do compile } */
-/* { dg-options "-O -fdump-tree-ifcombine" } */
+/* { dg-options "-O -fdump-tree-ifcombine-details-blocks" } */
 
 void bar (void);
 
@@ -34,3 +34,4 @@ foo2 (unsigned int a)
 
 /* { dg-final { scan-tree-dump "optimizing bits or bits test" "ifcombine" } } 
*/
 /* { dg-final { scan-tree-dump "optimizing double bit test" "ifcombine" } } */
+/* { dg-final { scan-tree-dump-not "Invalid sum" "ifcombine" } } */
Index: testsuite/gcc.dg/tree-ssa/ssa-ifcombine-7.c
===================================================================
--- testsuite/gcc.dg/tree-ssa/ssa-ifcombine-7.c (revision 245134)
+++ testsuite/gcc.dg/tree-ssa/ssa-ifcombine-7.c (working copy)
@@ -1,5 +1,5 @@
 /* { dg-do compile } */
-/* { dg-options "-O -fdump-tree-ifcombine" } */
+/* { dg-options "-O -fdump-tree-ifcombine-details-blocks" } */
 
 int test1 (int i, int j)
 {
@@ -12,3 +12,4 @@ int test1 (int i, int j)
 /* The above should be optimized to a i > j test by ifcombine.  */
 
 /* { dg-final { scan-tree-dump " > " "ifcombine" } } */
+/* { dg-final { scan-tree-dump-not "Invalid sum" "ifcombine" } } */
Index: testsuite/gcc.dg/tree-ssa/ssa-ifcombine-8.c
===================================================================
--- testsuite/gcc.dg/tree-ssa/ssa-ifcombine-8.c (revision 245134)
+++ testsuite/gcc.dg/tree-ssa/ssa-ifcombine-8.c (working copy)
@@ -1,5 +1,5 @@
 /* { dg-do compile } */
-/* { dg-options "-O -fno-trapping-math -fdump-tree-ifcombine" } */
+/* { dg-options "-O -fno-trapping-math -fdump-tree-ifcombine-details-blocks" } 
*/
 
 double test1 (double i, double j)
 {
@@ -22,3 +22,4 @@ plouf:
    Instead we get u<=, which is acceptable with -fno-trapping-math.  */
 
 /* { dg-final { scan-tree-dump " u<= " "ifcombine" } } */
+/* { dg-final { scan-tree-dump-not "Invalid sum" "ifcombine" } } */
Index: testsuite/gcc.dg/tree-ssa/ssa-ifcombine-9.c
===================================================================
--- testsuite/gcc.dg/tree-ssa/ssa-ifcombine-9.c (revision 245134)
+++ testsuite/gcc.dg/tree-ssa/ssa-ifcombine-9.c (working copy)
@@ -1,5 +1,5 @@
 /* { dg-do compile } */
-/* { dg-options "-O2 -fno-trapping-math -fdump-tree-ifcombine" } */
+/* { dg-options "-O2 -fno-trapping-math -fdump-tree-ifcombine-details-blocks" 
} */
 
 void f ();
 enum Sign { NEG=-1, ZERO, POS };
@@ -19,3 +19,4 @@ void g (double x)
    The transformation would also be legal with -ftrapping-math.  */
 
 /* { dg-final { scan-tree-dump "optimizing.* < " "ifcombine" } } */
+/* { dg-final { scan-tree-dump-not "Invalid sum" "ifcombine" } } */
Index: testsuite/gcc.dg/tree-ssa/threadbackward-1.c
===================================================================
--- testsuite/gcc.dg/tree-ssa/threadbackward-1.c        (revision 0)
+++ testsuite/gcc.dg/tree-ssa/threadbackward-1.c        (working copy)
@@ -0,0 +1,9 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-ethread" } */
+char *c;
+int t()
+{
+  for (int i=0;i<5000;i++)
+    c[i]=i;
+}
+/* { dg-final { scan-tree-dump-times "Registering FSM jump thread" 1 
"ethread"} } */
Index: tree-ssa-ifcombine.c
===================================================================
--- tree-ssa-ifcombine.c        (revision 245134)
+++ tree-ssa-ifcombine.c        (working copy)
@@ -332,6 +332,51 @@ recognize_bits_test (gcond *cond, tree *
   return true;
 }
 
+
+/* Update profile after code in outer_cond_bb was adjuted so
+   outer_cond_bb has no condition.  */
+
+static void
+update_profile_after_ifcombine (basic_block inner_cond_bb,
+                               basic_block outer_cond_bb)
+{
+  edge outer_to_inner = find_edge (outer_cond_bb, inner_cond_bb);
+  edge outer2 = (EDGE_SUCC (outer_cond_bb, 0) == outer_to_inner
+                ? EDGE_SUCC (outer_cond_bb, 1)
+                : EDGE_SUCC (outer_cond_bb, 0));
+  edge inner_taken = EDGE_SUCC (inner_cond_bb, 0);
+  edge inner_not_taken = EDGE_SUCC (inner_cond_bb, 1);
+  
+  if (inner_taken->dest != outer2->dest)
+    std::swap (inner_taken, inner_not_taken);
+  gcc_assert (inner_taken->dest == outer2->dest);
+
+  /* In the following we assume that inner_cond_bb has single predecessor.  */
+  gcc_assert (single_pred_p (inner_cond_bb));
+
+  /* Path outer_cond_bb->(outer2) needs to be merged into path
+     outer_cond_bb->(outer_to_inner)->inner_cond_bb->(inner_taken)
+     and probability of inner_not_taken updated.  */
+
+  outer_to_inner->count = outer_cond_bb->count;
+  inner_cond_bb->count = outer_cond_bb->count;
+  inner_taken->count += outer2->count;
+  outer2->count = 0;
+
+  inner_taken->probability = outer2->probability
+                            + RDIV (outer_to_inner->probability
+                                    * inner_taken->probability,
+                                    REG_BR_PROB_BASE);
+  if (inner_taken->probability > REG_BR_PROB_BASE)
+    inner_taken->probability = REG_BR_PROB_BASE;
+  inner_not_taken->probability = REG_BR_PROB_BASE
+                                - inner_taken->probability;
+
+  outer_to_inner->probability = REG_BR_PROB_BASE;
+  inner_cond_bb->frequency = outer_cond_bb->frequency;
+  outer2->probability = 0;
+}
+
 /* If-convert on a and pattern with a common else block.  The inner
    if is specified by its INNER_COND_BB, the outer by OUTER_COND_BB.
    inner_inv, outer_inv and result_inv indicate whether the conditions
@@ -394,6 +439,7 @@ ifcombine_ifandif (basic_block inner_con
        outer_inv ? boolean_false_node : boolean_true_node);
       update_stmt (outer_cond);
+      update_profile_after_ifcombine (inner_cond_bb, outer_cond_bb);
 
       if (dump_file)
        {
          fprintf (dump_file, "optimizing double bit test to ");
@@ -471,6 +518,7 @@ ifcombine_ifandif (basic_block inner_con
       gimple_cond_set_condition_from_tree (outer_cond,
        outer_inv ? boolean_false_node : boolean_true_node);
       update_stmt (outer_cond);
+      update_profile_after_ifcombine (inner_cond_bb, outer_cond_bb);
 
       if (dump_file)
        {
@@ -554,6 +602,7 @@ ifcombine_ifandif (basic_block inner_con
       gimple_cond_set_condition_from_tree (outer_cond,
        outer_inv ? boolean_false_node : boolean_true_node);
       update_stmt (outer_cond);
+      update_profile_after_ifcombine (inner_cond_bb, outer_cond_bb);
 
       if (dump_file)
        {

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