This patch fixes an exponential issue in ccmp.c.

This patch fixes an exponential issue in ccmp.c.  When deciding which ccmp
expansion to use, the tree nodes gs0 and gs1 are fully expanded twice.  If
they contain more CCMP opportunities, their subtrees are also expanded twice.
When the trees are complex the expansion takes exponential time and memory.
As a workaround in GCC6 compute the cost of the first expansion early, and
only try the alternative expansion if the cost is low enough.  This rarely
affects real code, eg. SPECINT2006 has identical codesize.

2016-02-04  Wilco Dijkstra  <wdijkstr@arm.com>

    gcc/
	PR target/69619
	* ccmp.c (expand_ccmp_expr_1): Avoid evaluating gs0/gs1
	twice when complex.

    gcc/testsuite/
	PR target/69619
	* gcc.dg/pr69619.c: Add new test.

From-SVN: r233145

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index c76070f8af1fe4468f18dd416c47ded54b250bf8..7c2dae8528723c9d045db93ff2327f175aede1c5 100644 (file)
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,9 @@
+2016-02-04  Wilco Dijkstra  <wdijkstr@arm.com>
+
+       PR target/69619
+       * ccmp.c (expand_ccmp_expr_1): Avoid evaluating gs0/gs1
+       twice when complex.
+
 2016-02-04  Mike Frysinger  <vapier@gentoo.org>
 
        * doc/invoke.texi: Delete -mno-fma4.

diff --git a/gcc/ccmp.c b/gcc/ccmp.c
index 9f1ce295554d17c0c3e39676632a07cabe7d5493..6f95acec95b547b5efb67152d373a174b4ac092c 100644 (file)
--- a/gcc/ccmp.c
+++ b/gcc/ccmp.c
@@ -170,7 +170,7 @@ expand_ccmp_expr_1 (gimple *g, rtx *prep_seq, rtx *gen_seq)
          int unsignedp0, unsignedp1;
          rtx_code rcode0, rcode1;
          int speed_p = optimize_insn_for_speed_p ();
-         rtx tmp2, ret = NULL_RTX, ret2 = NULL_RTX;
+         rtx tmp2 = NULL_RTX, ret = NULL_RTX, ret2 = NULL_RTX;
          unsigned cost1 = MAX_COST;
          unsigned cost2 = MAX_COST;
 
@@ -183,19 +183,25 @@ expand_ccmp_expr_1 (gimple *g, rtx *prep_seq, rtx *gen_seq)
                                        gimple_assign_rhs1 (gs0),
                                        gimple_assign_rhs2 (gs0));
 
-         tmp2 = targetm.gen_ccmp_first (&prep_seq_2, &gen_seq_2, rcode1,
-                                        gimple_assign_rhs1 (gs1),
-                                        gimple_assign_rhs2 (gs1));
-
-         if (!tmp && !tmp2)
-           return NULL_RTX;
-
          if (tmp != NULL)
            {
              ret = expand_ccmp_next (gs1, code, tmp, &prep_seq_1, &gen_seq_1);
              cost1 = seq_cost (safe_as_a <rtx_insn *> (prep_seq_1), speed_p);
              cost1 += seq_cost (safe_as_a <rtx_insn *> (gen_seq_1), speed_p);
            }
+
+         /* FIXME: Temporary workaround for PR69619.
+            Avoid exponential compile time due to expanding gs0 and gs1 twice.
+            If gs0 and gs1 are complex, the cost will be high, so avoid
+            reevaluation if above an arbitrary threshold.  */
+         if (tmp == NULL || cost1 < COSTS_N_INSNS (25))
+           tmp2 = targetm.gen_ccmp_first (&prep_seq_2, &gen_seq_2, rcode1,
+                                          gimple_assign_rhs1 (gs1),
+                                          gimple_assign_rhs2 (gs1));
+
+         if (!tmp && !tmp2)
+           return NULL_RTX;
+
          if (tmp2 != NULL)
            {
              ret2 = expand_ccmp_next (gs0, code, tmp2, &prep_seq_2,

diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 66115f01555c97cfa34c7a3ae29c35e40fc15aab..f2f73b609fd4962e0c0ecfb18621b721ae140590 100644 (file)
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2016-02-04  Wilco Dijkstra  <wdijkstr@arm.com>
+
+       PR target/69619
+       * gcc.dg/pr69619.c: Add new test.
+
 2016-02-04  Richard Sandiford  <richard.sandiford@arm.com>
 
        PR rtl-optimization/69577

diff --git a/gcc/testsuite/gcc.dg/pr69619.c b/gcc/testsuite/gcc.dg/pr69619.c
new file mode 100644 (file)
index 0000000..a200bdf
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr69619.c
@@ -0,0 +1,20 @@
+/* { dg-do compile } */
+/* { dg-options "-O3" } */
+
+int a, b, c, d;
+int e[100];
+void
+fn1 ()
+{
+  int *f = &d;
+  c = 6;
+  for (; c; c--)
+    {
+      b = 0;
+      for (; b <= 5; b++)
+       {
+         short g = e[(b + 2) * 9 + c];
+         *f = *f == a && e[(b + 2) * 9 + c];
+       }
+    }
+}