[PATCH] Fix PR 29333: Jump threading getting in the way of PHI-OPT

[Andrew Pinski]

Hi,
  The problem here is not really jump threading getting in the way of
PHI-OPT rather there is no cleanup of the IR after jump thread but
before phi-opt.
This patch adds a pass_phi_only_cprop right after the first vrp and
pass_merge_phi right before the first and last phiopts.

Since VRP does jump threading just like DOM does, we need a
pass_phi_only_cprop right after it.  And the merge PHI pass should be
done so that going into PHI-OPT we have a CFG which there is only one
PHI for a case like:
bb0:
if (a)
  goto L1;
bb3:
if (b) goto L2;
L1:
x = PHI <b(3), c(0)>
L2:
 x= PHI<x(L1), d(3)>

PHI-OPT does not handle PHIs like this that well.

OK? Bootstrapped and tested on x86_64-linux-gnu with no regressions.

Thanks,
Andrew Pinski

ChangeLog:
* passes.c (init_optimization_passes): Add pass_phi_only_cprop after
the first vpr pass.
Add pass_merge_phi before the first and last phiopt passes.

testsuite/ChangeLog:
* gcc.dg/tree-ssa/phi-opt-7.c: New testcase.

Index: testsuite/gcc.dg/tree-ssa/phi-opt-7.c
===================================================================
--- testsuite/gcc.dg/tree-ssa/phi-opt-7.c       (revision 0)
+++ testsuite/gcc.dg/tree-ssa/phi-opt-7.c       (revision 0)
@@ -0,0 +1,25 @@
+/* { dg-do compile } */
+/* { dg-options "-O -fdump-tree-phiopt1" } */
+
+
+int minmax_correct(int a)
+{
+        if (a > 32767) a = 32767;
+        else if (a < -32768) a = -32768;
+
+        return a;
+}
+
+int minmax_wrong(int a)
+{
+        if (a > 32767) a = 32767;
+        if (a < -32768) a = -32768;
+
+        return a;
+}
+
+/* { dg-final { scan-tree-dump-not "if" "phiopt1" } } */
+/* { dg-final { scan-tree-dump-times "MAX_EXPR" 2 "phiopt1" } } */
+/* { dg-final { scan-tree-dump-times "MIN_EXPR" 2 "phiopt1" } } */
+/* { dg-final { cleanup-tree-dump "phiopt1" } } */
+
Index: passes.c
===================================================================
--- passes.c    (revision 183396)
+++ passes.c    (working copy)
@@ -1302,9 +1302,11 @@ init_optimization_passes (void)
       NEXT_PASS (pass_copy_prop);
       NEXT_PASS (pass_merge_phi);
       NEXT_PASS (pass_vrp);
+      NEXT_PASS (pass_phi_only_cprop);
       NEXT_PASS (pass_dce);
       NEXT_PASS (pass_cselim);
       NEXT_PASS (pass_tree_ifcombine);
+      NEXT_PASS (pass_merge_phi);
       NEXT_PASS (pass_phiopt);
       NEXT_PASS (pass_tail_recursion);
       NEXT_PASS (pass_ch);
@@ -1401,6 +1403,7 @@ init_optimization_passes (void)
       NEXT_PASS (pass_late_warn_uninitialized);
       NEXT_PASS (pass_dse);
       NEXT_PASS (pass_forwprop);
+      NEXT_PASS (pass_merge_phi);
       NEXT_PASS (pass_phiopt);
       NEXT_PASS (pass_fold_builtins);
       NEXT_PASS (pass_optimize_widening_mul);